HomeMy WebLinkAboutUtility Emergencies Guide (final 012021) Fresno Fire Department
December 2020 Page 1
Fresno Fire Department Utility Emergencies Guide
Fresno Fire Department
December 2020 Page 2
Table of Contents
WATER TRANSMISSION ..................................................................................... 6
Supply Systems ..................................................................................................... 6
Pump Systems ............................................................................................ 6
Distribution Systems .............................................................................................. 6
Trunk Lines ................................................................................................. 6
Mains ........................................................................................................... 6
Service and Customer Lines ....................................................................... 7
Service ................................................................................................................... 7
Components ........................................................................................................... 8
Access ......................................................................................................... 8
Shut-off Valves ............................................................................................ 8
Indicating Type Valve .................................................................................. 9
Water Meters and Detector Check Valves ................................................ 10
Pressure Reducing Valves ........................................................................ 12
Location ............................................................................................................... 12
Single Family Dwelling .............................................................................. 13
Hotels ........................................................................................................ 13
Apartments ................................................................................................ 13
Commercial ............................................................................................... 14
High Rise ................................................................................................... 15
Fire Protection Systems ....................................................................................... 16
Sprinkler Systems ..................................................................................... 16
Standpipe Systems ................................................................................... 16
OPERATIONAL GUIDELINES ............................................................................ 17
DOMESTIC SERVICES ....................................................................................... 17
Outside ...................................................................................................... 17
Inside ......................................................................................................... 18
Fire Protection Services ....................................................................................... 19
Sheared Hydrant .................................................................................................. 19
Location ..................................................................................................... 20
Operation .................................................................................................. 20
Communication ......................................................................................... 20
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GAS UTILITIES ................................................................................................... 22
Properties Of Natural Gas .................................................................................... 22
Transmission And Storage ................................................................................... 22
Gas Equipment And Meters ................................................................................. 23
Meter Set Assemblies ............................................................................... 23
Residential Meter Set Assemblies ............................................................. 23
Industrial Meter Set Assemblies ................................................................ 25
Multiple Meter Set Assemblies .................................................................. 26
Branch Service .......................................................................................... 26
Shutoff Valves ...................................................................................................... 26
Stopcocks .................................................................................................. 26
Nordstrum Valve ....................................................................................... 27
Gate Valves ............................................................................................... 27
Curb Valves ............................................................................................... 27
Leaks Inside Structures ....................................................................................... 28
Leaks Outside Structures ..................................................................................... 30
Leaks With Fire .................................................................................................... 31
ELECTRICAL EMERGENCIES ........................................................................... 32
Electric Safety Awareness ................................................................................... 32
Key Points ................................................................................................. 32
Operating Around Energized Electrical Hazards .................................................. 33
Down Power Lines and Vehicles ............................................................... 33
Sub-Station, Transformer, Electrical Vault and Manhole Fire .................... 34
Power Pole Fires ....................................................................................... 34
SOLAR PHOTOVOLTAIC SYSTEM SAFETY AND THE FIRE GROUND ......... 36
Firefighter Safety Around Solar Photovoltaic Systems ......................................... 37
Background ............................................................................................... 37
Solar Systems: “Knowing The Difference” ........................................................... 37
Solar Photovoltaic ................................................................................................ 37
Solar Thermal ...................................................................................................... 38
Solar Co-Generation ............................................................................................ 39
SOLAR PV SYSTEM COMPONENTS ................................................................ 41
Photovoltaic Cell .................................................................................................. 41
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Module/Array ............................................................................................. 41
Photovoltaic Inverters And Disconnects ............................................................... 42
Inverters .................................................................................................... 42
Disconnects ............................................................................................... 44
Solar PV System Labeling ................................................................................... 45
THE PHOTOVOLTAIC SYSTEM: HOW IT WORKS! .......................................... 49
Basic PV System Overview—“Grid-Tied” and Off-Grid” ....................................... 49
“Grid-Tied” PV Systems ............................................................................ 49
Direct Grid-Tied PV Systems .................................................................... 50
Grid-Tied PV with Battery Back-up Storage System ................................. 51
“Off-Grid” PV System ................................................................................ 52
Solar PV System Recognition .............................................................................. 54
Roof-Mounted PV Systems ....................................................................... 54
Ground Mounted PV Systems ................................................................... 54
EFFECTS OF LIGHT ON PV SYSTEMS ............................................................ 56
Daylight ..................................................................................................... 56
Nighttime ................................................................................................... 56
PV SYSTEM HAZARDS ...................................................................................... 58
Hazardous Materials Inhalation Hazard ............................................................... 58
PV System Battery Hazard ........................................................................ 58
INCIDENT PRIORITIES AND TACTICAL CONSIDERATIONS .......................... 59
Communications .................................................................................................. 59
Securing Utilities .................................................................................................. 59
Fire Attack Considerations ................................................................................... 60
Ventilation Considerations ................................................................................... 61
DEFINITIONS ...................................................................................................... 62
REFERENCES .................................................................................................... 66
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INTRODUCTION
This Guide covers Utility Emergencies including Water, Gas, and Electricity. The
Fire Department is called to help solve problems such as flooding, gas leaks, and
power lines down or electrical emergencies. These often result in the need to
quickly contain or isolate the problem or hazard. The following guidelines present
an approach which will apply in many situations, but do not replace good
judgment and experience in dealing with any incident. The guidelines should be
used whenever situations are encountered that do not clearly indicate that a
different approach is required to safely resolve the hazard.
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WATER TRANSMISSION
Supply Systems
When water is pumped from the underground aquifer and from the Surface Water
Treatment Facility, it is distributed through a transmission grid main system to
individual customers.
1,780 miles of distribution pipeline
140,992 service connections
12,952 fire hydrants
18,942 main line valves
260 active pump stations
Pump Systems
When a source of water is below or at the same elevation as a municipality, or
cannot naturally provide sufficient pressure through adequate elevation, pumps are
used to supply water at the proper pressure into a distribution system.
Distribution Systems
Water is delivered throughout Fresno City by a distribution system of pipes, valves,
check valves, and water meters, and is normally cross connected at specific
intervals to supply water to areas that can be affected by repairs, breakage, and
other similar problems. Pipelines within a distribution system can be classified as
trunk lines, mains, service, and customer lines.
Trunk Lines
Trunk lines carry water from a primary source (reservoirs, pumps, etc.) to mains
within a distribution system. Trunk lines can vary from 36-inches to 10-feet in size
and are constructed from iron or concrete.
Mains
Mains normally run beneath a street and parallel to a curb, can vary from 2 to 72-
inches in size, and are constructed from iron pipe. Mains can be cross connected to
form loops that allow shutting down a specific main within a distribution system for
repairs, etc.
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Service and Customer Lines
Water is delivered to individual structures by a combination of service and customer
lines. Service lines run between a main and a water meter, can vary from ½-inch to
12-inches, and are constructed from iron, copper, or galvanized pipe. Customer
lines run between a water meter and a structure, can vary from ½-inch to 12-inches,
and are constructed from iron, copper, galvanized, or plastic pipe.
Figure 1 - Customer and Service Line
Water utility companies are normally responsible for maintenance and repair of a
water distribution system, including:
Water metering device.
Shut-off valves on either side of a water metering device.
Building owners are normally responsible for maintenance and repair of:
Plumbing from the shut-off valve (on the output side of a water metering
device), and into a structure.
All plumbing inside a structure.
Service
The type and size of water service to a structure is determined by a combination of
applicable plumbing code requirements and water consumption needs that result in
the following types of water service configurations:
WATER METER
PRESSURE REDUCING VALVE
SHUT OFF VALVE
VAULT
CUSTOMER
RESPONSIBILITY
WATER UTILITY
RESPONSIBILITY
SHUT OFF VALVES
(CURB VALVES)
SERVICE LINE
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Domestic water only.
Domestic water and water for fire protection through a single service.
Domestic water and water for fire protection through separate services.
Components
Water service systems are comprised of shut-off valves, water meters and detector
check valves, and pressure reducing valves.
Access
A meter box, vault, or manhole often has a centerpiece or lid with a hole that can
be utilized to remove the cover. The centerpiece or lid normally identifies the type of
utility with the word(s) "WATER," or "CITY WATER METER.”
Figure 2 - Meter Box, Vault, Manhole
Shut-off Valves
Shut-off valves (or service valves, curb valves, etc.) provide a means for controlling
the flow of water through service and customer lines. Two types of shut-off valves
are commonly utilized:
Non-Indicating Valves
These valves do not indicate an open or closed position and are
characterized by ball or cone valves and gate valves.
A ball or cone valve has a rectangular valve-nut attachment on the top of
the valve. When the valve is closed, the valve-nut is perpendicular to the
valve.
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Figure 3 - Ball or Cone Valve
A gate valve is a non-rising stem valve that has a square valve-nut
attachment at the top of the valve stem.
Figure 4 - Gate Valve
Indicating Type Valve
These valves indicate an open or closed position and are characterized by
Outside Stem and Yoke (OS&Y) valves and post indicator valves (PIV).
An OS&Y valve has a rising stem type valve.
Figure 5 - OS&Y Valve
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A Post Indicator Valve (PIV) is connected to an underground gate valve.
Figure 6 - Post Indicator Valve
Water Meters and Detector Check Valves
Water meters are used to calculate water usage and check valves are utilized to
allow the flow of water in one direction only. The type of meter and/or check valve is
dependent on the type of water service as follows:
Water Meter is used to calculate water usage for a domestic water service.
Water meters are normally directly adjacent to shut-off valves and vary in
size from ½ to 10-inches (inlet-outlet size).
Figure 7 - Water Meter
Compound Meter is used to calculate water usage for domestic water
services that can use low and high-water flows. During low water flows, a
compound meter operates as a standard water meter. However, if high
flows are necessary, a check valve opens and allows the passage of large
flows that are metered separately. Compound meters are 4-inches or
larger and are normally found directly adjacent to shut-off valves.
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Figure 8 - Compound Meter
Detector Check Valve with By-Pass Meter. Used to supply water for a
closed fire protection system. When necessary, a check valve opens and
allows water to flow straight through unmetered. In the closed position, the
check valve prevents water from flowing back into a water distribution system
(i.e., from Fire Department apparatus pumping into a standpipe inlet). Most
detector check valves will use a small water meter in parallel with the check
valve(s) to detect leaks and the unauthorized use of water. Detector check
valves can vary in size from 2 to 10-inches.
Figure 9 - Detector Check Valve with By-Pass Meter
Combination Water Service - A domestic water meter and detector check
valve providing separate water services. Water meter and check valve
may be in the same vault or separated in adjacent vaults.
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Figure 10 - Domestic Water Meter and Detector Check Valve
Pressure Reducing Valves
Pressure Reducing Valves are normally used in domestic services to reduce high
water pressures to an acceptable level inside a structure (i.e., dwellings commonly
use 40 to 80 psi). Pressure reducing valves are not normally utilized in fire
protection services.
Figure 11 - Pressure Reducing Valves
Location
The order of placement for water system components between a main and
structure can vary. A typical domestic water service normally consists of piping, a
water meter, shut-off valve(s), a pressure reducing valve, and a typical fire protection
service normally consists of piping, detector check valves, and shut-off valves.
In warm climates, water meters can be placed just below grade level, and pressure
reducing valves, shut-off valves, and detector check valves can be located above or
below grade level.
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The following are general considerations for single family dwellings, apartments,
hotels, commercials, and high rises:
Single Family Dwelling
Domestic water services will normally consist of a ½ to 2-inch single water meter
with shut-off valve on one or both sides of a meter. A customer line runs
underground from the meter to a vertical riser that enters a structure on the exterior
or in a basement. A pressure reducing valve can be located near the meter or
structure. Water service for a domestic sprinkler system will normally be a 2-inch
detector check valve that is in a separate vault.
Hotels
Domestic water and fire protection services are provided by a combination water
service that provides domestic water with a 4-to-6-inch water meter and water for
fire protection with a 4-to-8-inch detector check valve. Shut-off valves are normally
adjacent to the water meter and detector check valves, and a post-indicator valve is
normally present between the detector check valves and structure. The water meter
and detector check valves can be in the same vault, separate vaults, or above
ground.
Apartments
Domestic water service will normally consist of 1-to-3-inch customer lines and a
single 1-to-3-inch water meter with a shut-off valve on one or both sides of a meter.
Like single family dwellings, and depending on water requirements, a customer line
runs underground from a water meter to a vertical riser that enters a structure on the
exterior or interior. A pressure reducing valve can be located near the water meter
or structure. Water service for fire protection will vary between 2-to-4-inches.
The water services for domestic water and fire protection are in separate below
ground vaults or located above ground. A common alternative to a single 1-to-3-inch
water meter is a 3-inch equivalent water service. This system consists of two 2-inch
water meters in adjacent vaults that are connected to a single 3-inch customer line
that enters a structure on the exterior or basement. In this configuration, the pressure
reducing valve is located near the structure.
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Figure 12 - Domestic Water Service Configured for Apartment
Note: If a structure has Dorothy Mae Sprinklers, a separate 2-inch fire
service vault is used.
Commercial
Water services to these types of structures are not primarily based on the size of a
structure but will depend on the water requirements of a structure. As an example,
a large warehouse with a small office area and large storage area can have a large
(4 to 10-inch) water service for fire protection and a small (1 to 2-inch) water service
for a domestic water system. Conversely, a moderate size commercial occupancy
can have a 2-to-4-inch service for fire protection and a large (4 to 8-inch) domestic
water service for specific requirements. Common applications are as follows:
A commercial occupancy with multiple occupancies (such as mini-malls),
can be serviced with water for a domestic water service by a single water
meter for an entire building or, by multiple, 1-to-2-inch water meters in
separate vaults, which can supply each individual occupancy (referred to
as a battery).
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Figure 13 - Multiple 1 to 2-inch Water Meters in Separate Vaults
1-to-2-inch water meter for domestic water service and 2-to-4-inch detector
check valves for fire protection in separate vaults. Shut-off valves are
normally adjacent to a water meter. Detector check valves and a post
indicator valve should be present between the detector check valves and
structure.
Combination water service with a 4-to-8-inch water meter for domestic
water service, and 4-to-10-inch detector check valves for fire protection in
the same vault. This configuration is used for large water volumes. Shut-
off valves are normally adjacent to a water meter and detector check
valves and a post- indicator valve should be present between the detector
check valves and structure.
Shut-off valves are normally adjacent to water meters in separate vaults or
a single meter that serves an entire building. Water for fire protection can
be provided by detector check valves in a separate vault, or in a common
vault with a water meter that serves an entire building. Shut-off valves are
normally adjacent to detector check valves and a post indicator valve may
be present between the detector check valves and structure.
High Rise
Domestic water and fire protection service is provided by a combination water
service that consists of a 4-to-10-inch water meter for domestic water and 4-to-12-
inch detector check valves for fire protection in the same vault. Above ground risers
may be present for domestic and fire protection services. Shut-off valves are
normally adjacent to water meters and detector check valves in this type of
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configuration. Post-indicator valves are normally present between the detector
check valves and structure.
Fire Protection Systems
Fire protection is provided by sprinkler systems and standpipe systems.
Sprinkler Systems
Automatic Wet Pipe System. The pipes in this system are always filled
with water. When a head is activated, water immediately flows from
activated heads. Water is supplied to this system by gravity tank, pressure
tank, automatic fire pump, or a water service system.
Automatic Dry Pipe System. The pipes are filled with compressed air.
When a head is activated, air is immediately released from activated
heads. This causes a drop in air pressure, which allows water to enter the
system and flow from activated heads. Water is supplied to this system by
a gravity tank, pressure tank, automatic fire pump, or a water service
system.
Non-Automatic System. Pipes are maintained dry. To charge this system
with water, it is necessary for fire department apparatus to pump into the
fire department connection to supply water to activated heads.
Deluge System. Sprinklers may be open or closed and are supplied with
water by a heat actuated valve. Water is supplied to this system by a
gravity tank, pressure tank, automatic fire pump, or a water service system.
Standpipe Systems
Dry Standpipe. Dry standpipes consist of a Siamese connection, piping,
and 2½-inch outlets on each floor (stairway and/or fire escape balcony) and
roof. Water is supplied to this system by fire department apparatus.
Wet Standpipe. Designed for occupant use and consists of 100' of 1½”
unlined single jacketed hose with a ½” straight tip with no shut-off.
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OPERATIONAL GUIDELINES
DOMESTIC SERVICES
For leaks outside a structure, use multiple personnel to locate the
appropriate shut-off location (one person may not find the correct location
in the least amount of time).
For leaks inside a structure, use multiple personnel to simultaneously
investigate the interior and exterior of a structure to locate the most
appropriate shut-off location. This approach will enhance the ability of
personnel to locate the appropriate shut-off location in a timely manner.
Occasionally a shut-off valve may be encountered with a sign as follows:
"LIFE SUPPORT MACHINE IN AREA" or "SHUT GATE SYSTEM DIVIDE.
" DO NOT turn these valves off unless appropriate approval is obtained.
When closing a ball, cone, or gate valves that are 3-inches or larger, it may
be necessary to exercise a valve to eliminate the flow of water as valves
can become encrusted with rust and scale. When a stubborn cone valve is
encountered, slightly loosen the nut on the bottom of the valve (if
accessible) and strike the threaded shaft with a hammer. This will drive the
shaft into the valve and free the valve. The valve may now be shut off.
Ball and cone valves can be identified by the lack or presence of a nut on
the bottom of a valve. Ball valves do not have a nut on the bottom of a
valve, and cone valves do.
All shut-off valves should be slowly closed and opened to avoid water
hammer.
Outside
Shutting off water leaks that are located outside of structures are normally limited to
leaks in mains, service lines, or customer lines and are normally handled by utility
company personnel. Leaks in customer lines (between a water meter, detector
check valve, and structure) are normally handled by fire service personnel as follows:
3/4-to-1-inch service:
A shut-off valve (ball or cone valve) is normally located adjacent to a water
meter and may be located above ground or underground. If the valve is
underground and not in a meter box it may be necessary to dig down outside
a meter box to access the valve. Turning these valves 90 degrees will
eliminate the flow of water.
1-to-3-inch equivalent service:
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A shut-off valve (ball or cone valve) is normally located on both sides of a
water meter. Remove each vault cover to access the meter valves. It is
necessary to shut off a valve in both vaults to eliminate the flow of water past
this service configuration.
4-inch and larger:
Gate valves are located on both sides of a water meter. When closing these
valves, remember it may be necessary to exercise a valve to eliminate the
flow of water. Large above ground or underground installations may consist
of back flow valves that are in line with the water meter and multiple OS&Y or
gate valves. Due to the size of these water services and the possibility of
damage to building heating, cooling, and other similar systems, personnel
should not close these valves unless necessary. Normally, the DWP should
be requested to handle these systems.
Inside
Shutting off water leaks that are located inside of structures can be accomplished
as follows:
Depending on the type of leak, closing accessible shut-off valves near a
water meter or the globe valve that can normally be found on the vertical
riser that enters a structure will quickly eliminate the water service to the
interior of a structure until an interior leak is located and repaired.
Broken Pipes. Broken pipes in walls normally require shutting off the flow
of water to a structure using exterior shut-off valves near a water meter,
etc.
Toilets. Toilets are found in two configurations, residential and commercial.
Leaks from residential toilets can be easily eliminated by shutting off the
angle valve at the wall near the toilet. In these applications, plastic tubing
has replaced metal tubing and is more susceptible to splitting due to
hardening. Leaks from commercial toilets can be eliminated by removing a
cap over the relief valve and using a slot-head screwdriver to turn the relief
valve screw outward. This will let the valve seat and stop the flow of water
to the toilet.
Urinals. Leaks from commercial urinals can be eliminated by removing a
cap over the relief valve and using a slot-head screwdriver to turn the relief
valve screw outward.
Sinks and Residential Appliances. Leaks from sinks and other types of
residential appliances can normally be eliminated by shutting off the angle
valve(s) at the wall near the sink or appliance.
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Manufacturing Process. Leaks from a manufacturing process that utilizes
water will often have readily available shut-off valves near the process. If
these types of valves are not readily found, using exterior shut-off valves
may be necessary to eliminate the flow of water.
Hot water leaks can normally be eliminated by shutting off the appropriate
valve at a water heater or boiler. However, remember to shut off the gas or
electricity to the heater to prevent a possible rupture due to expanding
water in the heater.
Fire Protection Services
Depending upon the buildings system a partial system shut down or full system shut
down will control the water.
Sectional shut-off or Zone valves. Sprinklers can be controlled by using
the appropriate sprinkler shut-off tool, then look for sectional shut-off or
zone valves instead of shutting off the whole system. This will cause less
disruption of the system and speed up the draining process.
2-inch service:
A shut-off valve (ball or cone valve) is normally located adjacent to a
detector check valve. Turning this valve 90 degrees will eliminate the flow
of water past this service.
4-inch and larger service:
Indicating valves (post-indicator valve) can be used to eliminate the flow of
water past these valves. Post-indicator valves are located outside of
structures, are connected to an underground gate valve, and have a handle
or wrench to operate the valve. To operate a post-indicator valve, remove
any padlocks or chains securing the control valve. Turn valve in clockwise
direction to close the valve. The valve will visually indicate the position of
the valve by an arrow or display which states “OPEN” OR “SHUT.”
OS&Y valves that are normally located directly adjacent to detector check
valves on 4-inch and larger fire services are not normally used to eliminate
the flow of water past these valves. However, a gate valve should be
turned clockwise to stop the flow of water past this service. OS&Y valves
are turned clockwise (so the stem is not visible) to stop the flow of water.
Sheared Hydrant
Placement of apparatus for the protection of members is paramount. To insure
protection against injuries caused by debris being thrown into the air, the use of
protective clothing is recommended (helmet, goggles, turnouts, or rain gear).
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Location
The fire hydrant gate valve is normally found in direct line with the fire hydrant and
perpendicular to the curb. A six-inch diameter cap (usually painted blue) covers
access to the gate valve. Some gate valve locations are indicated by arrows etched
on the adjacent curb.
Operation
Remove gate valve cap. Place hydrant shut-off tool on gate valve stem. Turn in a
clockwise direction to close valve (your initial attempt should begin with a clockwise
rotation). Close the gate valve slowly to reduce the possibility of water hammer.
Two members applying moderate pressure to the gate key should be adequate
when closing the valve (fire hydrant gate valves may require 18 to 26 full turns to
complete a shutdown). If the gate valve will not turn in a clockwise direction, attempt
to close the valve in a counterclockwise direction. Caution must be taken, as
excessive force will cause damage or break the gate valve stem.
Note: Although approximately 98% of all fire hydrant gate valves close in a
clockwise direction, a member must recognize those instances when a
counterclockwise rotation is necessary to close the valve.
As the gate valve is operated, you will hear and feel the vibration of the valve as it
closes. If there is no decrease in the amount of water flow, you may be operating
the wrong valve, or the valve may be broken. If it has been determined the wrong
gate valve has been closed, return the valve to its original position. Always count the
number of full turns when closing fire hydrant gate valves.
Note: Fire hydrant gate valves should only be operated to shutdown sheared
hydrants. For leaking fire hydrants, follow procedures described in the
Manual of Operation, Volume 2, 4/2-34. 59 (J).
The sheared off hydrant should be secured in a safe location.
Communication
When notifying OCD of a sheared off fire hydrant, include the following:
Fire hydrant location.
State if fire hydrant has been shut-off.
The number of valves operated.
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OCD will notify the DWP Water Operating Trouble Board and advise them of your
actions. The DWP will then dispatch necessary resources to the location.
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GAS UTILITIES
INTRODUCTION
Natural gas is the product of nature’s action on organic material over millions of
years. It is a common source of heat in buildings due to its convenience,
abundance, and relatively low cost. Almost every structure in the City of Los
Angeles has natural gas delivered to the property, via underground service pipes.
Firefighters respond to natural gas incidents every day. This product is
considered safe, due to its relatively small window of flammability. However, if we
refuse to give it the proper attention, it will take advantage of our complacency.
We must train ourselves to be vigilant, and on the alert, for situations that can
injure or kill firefighters and/or the public that we serve.
Properties Of Natural Gas
Pure natural gas is completely odorless. For leak detection, odorant is added so
that as little as one-percent of natural gas in the air can be detected. The
common odorant is a Mercapitan/Thiophane mix, which is used in solution of one
pint per million cubic feet of gas. Natural gas is non-toxic and is not considered
hazardous when inhaled in limited concentrations. However, in quantities large
enough to displace oxygen, asphyxiation can occur.
Natural gas is lighter than air, which results in escaping natural gas rising and
rapidly dissipating. This is a distinct safety advantage over heavier fuels such as
butane and propane, which are heavier than air; and when escaping, it will collect
in low areas. Escaping natural gas can be hazardous when trapped by confined
spaces such as structures, hollow walls, etc. Natural gas also has an ignition
temperature of 1100 degrees and has a flammable range between 4 and 14
percent.
Transmission And Storage
Most natural gas is initially distributed through over 30,000 miles of transmission
lines from Texas, Kansas, New Mexico, Oklahoma, Arizona, and the Rocky
Mountain area. Transmission lines maintain pressures up to 1000 psi and use
pressure booster compressor stations, at specific intervals, to maintain
appropriate flow and pressures. To compensate for fluctuating demands, gas
companies can maintain underground or above ground storage facilities. Natural
gas is generally distributed by a combination of transmission lines and distribution
mains. Transmission lines bring natural gas into the Southern California area and
vary in diameter from 12 to 36-inches. Natural gas is then distributed to Gas
Company customers by distribution mains. The gas is carried by service lines at
medium pressure, which normally does not exceed 60 psi. At the service meter
(Meter Set Assembly), the pressure is reduced to a low pressure (approximately
1/3 psi.). Distribution mains are generally polyethylene and account for a high
percentage of the mains in use today. Older existing distribution mains are made
of steel or copper but are rare to find. Polyethylene mains are color coded to
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December 2020 Page 23
identify the pipe as transporting natural gas. These pipes are yellow, which is the
national color code for newer installations. Older installations of plastic pipe can
be pink (salmon beige), or orange in color.
Polyethylene will have a wire running the length of the pipe, for locating plastic
gas lines, below ground. Above ground gas lines must be made of steel and
cannot be plastic. Distribution mains are normally located underneath city streets,
parallel to curbs, under grassy parkways, between the curb and sidewalk, and
occasionally in alleys.
Gas Equipment And Meters
Meter Set Assemblies
Natural gas is distributed from a distribution main to the customer by a service
line. Service lines run from distribution mains to structures, via an outside riser,
where pressure regulators and meters are located. The pressure inside a
customer line (inside the structure) is low pressure (approximately 1/3 psi) and is
regulated and measured by a regulator and gas meter. Gas companies refer to
gas meters as Meter Set Assemblies (MSA's). MSA's can be found in the
following three locations:
Outside Sets - MSA's are located outside the structures.
Underneath Sets - MSA's are located underneath structures, stairs, etc.
Curb Meter Box - MSA's are in a vault underneath a sidewalk.
Cabinet Set - MSA’s are in an enclosure on the exterior of the structure.
Additionally, MSA's can be categorized as follows:
Residential
Industrial
Multiple Gas Meter
Residential Meter Set Assemblies
The basic MSA consists of piping, a shut-off valve, regulator, and gas meter. The
pipe rising vertically from the ground, close to the exterior wall of a structure is
called a riser. Tracing the riser up from the ground, the first fitting is the shut- off
valve called a stopcock or service cock. This valve is usually of primary concern
to the personnel responsible for shutting off the gas to a structure. Of particular
interest is the following:
A ring on the stopcock valve indicates a branch service.
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A flat washer on the stopcock valve indicates that the service line is a
plastic pipe inserted inside an older metal pipe.
A band on the stopcock valve indicates the service line is plastic.
Next, up the riser, is a flat circular device called a "regulator" that reduces
medium gas pressure (up to 60 psi) to a relatively low level of
approximately 1/3 psi.
Next are pipes and fittings, leading to the gas meter. The meter measures
the amount of gas that is used. After the meter, gas flows through pipes
and fittings into the structure.
Figure 14 - Meter Set Assembly
Shutoff valves can be located by finding the MSA since they are always adjacent
to each other. Initially, look for a "G" that is either chiseled or painted on the curb.
A "G", required by Cal-OSHA, marks the location where the service line passes
beneath the curb and indicates which side of the building the MSA is located. If a
"G" cannot be quickly found, do not waste time looking for one.
Next, look along the foundation of the structure. MSA's and shut-off valves are
normally located on an outside wall of a structure, in a location that is easily
accessible to gas company personnel who read the meters for billing purposes.
If an MSA is not visible along an outside wall, it is usually found in the following
location:
In a crawl space, under the building.
Beneath an outside staircase.
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In an outdoor cabinet, particularly new condos.
In an underground garage.
In a sidewalk or parkway vault, at the side of a building.
In a basement, with the shut-off valve usually accessible from the outside
of the building.
Subsurface, in the parkway or sidewalk.
Some MSA's may be equipped with an emergency vibration-sensitive shut off
device known as an earthquake valve. These valves are marketed by private
industry and are normally mounted on the discharge side, right side as you face
the meter, of an MSA. Earthquake valves take on various shapes and sizes and
can easily be mistaken for any number of gas appliances. Personnel should
recognize and understand that a swift-kick may possibly shut off the flow of gas,
but only in the event of a damaged or frozen stopcock; never done in lieu of a
normal shut-off procedure. Turning a reset button, one-quarter turn, completes
reset of this device.
Industrial Meter Set Assemblies
Industrial MSA's are similar to, and larger than, residential MSA's due to the
increased flow of gas (volume) that is necessary for commercial/industrial
applications. Industrial MSA's can be characterized by any of the following
features:
A curb valve and curb valve extension handle can be utilized to control the
flow of gas in the service main.
Industrial shut-off valves, known as Nordstrom valves, are used for high
pressure applications. They are larger than standard shut-off valves and
may require more effort and larger tools to shut off the flow of gas. Some
industrial installations have gate valves with wheel handles that may be
turned clockwise to close.
Industrial applications that are high pressure can use two regulators in
series to regulate the gas pressure. A rotary meter is used, instead of a
conventional MSA, to regulate the high pressure and handle quick surges.
Meters under the sidewalk, called curb meters, are common in commercial
areas. The lid over the curb meter space is made of lightweight concrete,
or fiberglass set in a metal frame, and is easily identified by its gas
company markings.
Industrial MSA's are physically larger than MSA's used for residential
applications.
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Multiple Meter Set Assemblies
Multiple habitational or commercial occupancies are often equipped with multiple
MSA's, which provide a master stopcock and a separate meter and stopcock for
each unit. Past the riser, and master stopcock, is a horizontal header that feeds
multiple stopcocks and MSAs. Master stopcocks shut off the entire building and
individual meters/stopcocks can control the flow of gas to individual occupancies
in one structure. The Gas Company is required to identify the individual MSA’s,
as to which unit or building they serve. If the identification has worn away, notify
The Gas Company to have the meters properly marked.
Branch Service
In some commercial areas, multiple structures may be commonly serviced by a
single service pipe called a standard service main. A metal ring identifies this
branch service. The occupancy that is further from the supply main is a standard
service, and the other occupancies are branch services. All MSA’s that are
served from the branch main will be identified by a ring at the stopcock.
Shutoff Valves
Stopcocks
To turn off the flow of gas, turn the tang, crosswise, to the flow of gas,
crosswise to the pipe. The tang on some stopcocks can be square. Turn
the tang, so the line on the tang is crosswise to the pipe. Tangs can be
easily turned with a crescent wrench.
If a tang appears to be stuck, do not apply too much pressure. If the tang
breaks off, it will be difficult to stop the flow of gas. It is recommended
that The Gas Company service a stuck tang. However, stuck tangs can be
approached in EMERGENCY CONDITIONS as follows:
1. Use two wrenches, one on the tang and the other on the backing nut.
Holding the tang steady, loosen the backing nut one-quarter turn only! If
the backing nut is loosened too far, the core can fly out, leaking
medium pressure gas, 40 to 60 psi. It is nearly impossible to replace
the core while gas is leaking. NOTE: Newer stopcocks have a pin
driven into the backing nut, and bolt, and cannot be loosened.
2. Give the backing nut a tap with a non-metallic hammer, freeing the
core.
3. Turn the tang, one-quarter turn, to stop the flow of gas; a half-turn will
continue to let the gas flow.
4. Tighten the backing nut to lock the core in the "OFF" position.
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Nordstrum Valve
The Nordstrum Valve is a larger version of a residential stopcock. It is
used on high-pressure risers and piping, at industrial/ commercial sites,
and comes in various sizes to fit different diameter pipes. The tang on a
Nordstrum valve can only be turned one-quarter turn, in either direction,
ensuring the "ON" and "OFF" positions are easy to locate. Depending on
the size of the valve, large wrenches may be necessary to turn this valve.
Figure 15 - Nordstrum Valve
Gate Valves
Some industrial meters are equipped with a gate valve that has a wheel
handle (like an OS&Y). Turning the handle clockwise several revolutions
will shut off the gas.
Curb Valves
Also referred to as an Emergency Shutoff Valve, these valves can be
installed in addition to stopcocks at public assembly occupancies such as
schools, hospitals, churches, etc. They are normally located near the
property line, by a sidewalk. They are two to three feet underground and
under a small metal, concrete, or fiberglass lid; with "Gas Company"
markings in raised letters. To gain access to this valve, lift the lid with a
common utility tool, screwdriver, in the hole. If the lid is stuck, and
additional leverage is necessary, insert the point of a pick head axe in the
hole and apply the proper leverage. This valve is an ordinary gate valve
with a "faucet" type handle. Turn the handle CLOCKWISE to stop the flow
of gas. If the valve is too deep to reach with the hand, a sprinkler key can
be used for extra reach.
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Remember that if this valve is present, either turning the gas off at the curb
valve or meter stopcock can eliminate the flow of gas.
Leaks Inside Structures
Natural gas emergencies can be divided into the three following categories:
Inside leaks
Outside leaks
Leaks resulting in fires
While each leak has its own dangers and concerns, the greatest danger results
from gas leaks inside structures, due to the potential for ignition and explosion.
The first priority upon arrival on the scene of a reported leaking natural gas
incident is safety. If a heavy odor of "gas" occurs, expect the worst. Expose as
few people as possible, meaning prompt evacuation where necessary. A faint
whiff of "gas" or a leak, which has “come and gone” for the past few days, may
allow more leeway to perform a leak examination.
For faint odors, always check the condition of pilot lights as a first action. If a leak is
suspected, pouring soapy water over the suspected area can confirm its presence.
When a leak is found, always try to isolate the area as close to the leak as
possible. Sometimes, turning the appliance valve near the problem one-quarter
turn, the leak can be stopped leaving the rest of the premises unaffected. If it is not
possible move back along the supply piping to the next point of control: generally,
another stopcock at the MSA.
Multi-meter service is often present in multiple-tenant occupancies, such as
apartment houses, or shopping centers. Each tenant has a meter and stopcock.
Additionally, where the service pipe comes through the slab, prior to the MSA’s,
there will be a "master" valve called the isolation valve stopcock, which stops the
flow to all tenants in the building on the service pipe. This valve should be used
with discretion, a minor leak at an appliance does not warrant shutting off 20 or 30
apartments. Conversely, if there is a major leak and difficulty is experienced in
determining which meter controls the appropriate apartment, the main service
stopcock provides the fastest means of control.
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Figure 16 - Multiple MSA (Header)
Tactical considerations at an inside leak should include the following
considerations:
Determining necessity and extent of evacuation.
Remove all sources of ignition. Avoid operating electrical switches.
Turning a switch "ON" or "OFF", can cause sparking. Also, avoid walking
on carpets in dry weather to prevent sparks from static electricity.
Turn off appliance valve located at the connection from the appliance to the
customer house line.
Open windows after all sources of ignition have been eliminated. This
ventilation can bring the gas into the proper explosive mixture with air.
Searching for occupants who may be overcome by gas.
If it is determined to be unsafe to enter the structure, consider the following:
o Turn off gas at the meter.
o Spot apparatus in safe zones.
o Establish a water supply and prepare for fire suppression
operations.
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Leaks Outside Structures
Outside leaks can be just as dangerous as inside leaks because gas can take the
path of least resistance, as it tries to escape to the atmosphere. Quite often, that
path is along the gas service pipe or other underground lines into buildings or
manholes. This migration may not be apparent because, as the gas travels
through the ground, it tends to deodorize as the soil filters out the odorant. The
best immediate procedure for responding to an outside leak should include the
following considerations:
Call the Gas Company. Allow the Gas Company representative the
opportunity to assess the situation and call for equipment. In large
emergencies, The Gas Company will send a management representative
as a liaison and spokesperson for the company. Only the Gas Company
can shut down a transmission or distribution line.
The Fire Department's role at the site is to maintain public safety. This
usually means eliminating potential sources of ignition until the leak is
stopped. Place apparatus upwind of the leak and away from manhole
covers, storm drains, or structures that can contain trapped gas. Evacuate
when appropriate and maintain site security. It can take several hours for
The Gas Company to shut off gas in a large, high-pressure, pipeline.
The only sure way to safely check suspected areas are to use a
combustible gas indicator. Currently, hazardous material squads carry
equipment that can be used to detect the presence of natural gas and its
lower explosive limit (LEL).
If the leak is adjacent to structure(s), close doors, and windows to prevent
gas from entering.
If gas ignites, protect exposures close enough to be damaged.
o Previously, The Gas Company used to teach its members a
technique, known as the bend-back method, for controlling the flow
of gas in small diameter pipes. This method is now against The Gas
Company’s policy, due to a recognized danger to their employees.
There is an extremely high potential for creating a static charge that
usually accompanies the increased pressure of gas flowing from the
restricted opening as the pipe is bent over.
Crimping plastic pipe is acceptable if all tools used to work on plastic pipe
are grounded.
Redwood plugs can be driven into various diameter steel pipes with a
rubber mallet. This method, redwood plugs, does not work with
polyethylene pipe.
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Be aware that, on rare occasions, pipelines may contain hazardous
contaminants such as Polychlorinated Biphenyls. The Gas Company
states that its product is 97 percent free from impurities. However, if any
liquid flows from a natural gas pipe, do not let it touch your body. Treat the
liquid as a hazardous material and notify the hazardous material squad.
Whenever a gas travels through piping, it can create a static electric charge
on the pipe. On steel pipe, the current is drawn off and safely dissipated to
the ground by the conductive pipe itself. Plastic pipe is an insulator, and it
is probable that the pipe will have a static charge. A person grabbing the
pipe to apply a plug will likely discharge this current, creating spark. Fog
down the plastic pipe with a wetting agent such as wet water to prevent
ignition from static electricity. Water alone tends to bead up and run off
polyethylene pipe, thus reducing the effectiveness of water. A wetting
agent such as wet water will add an adhesive quality to water that helps
ensure that a static charge cannot form. (Use water judiciously and avoid
flooding as mud hampers utility crews working at the break). Some plastic
pipes are equipped with a wire that is used to help work crews locate the
pipe from above ground. This wire provides no electrical charge.
Additionally, it should not be relied upon to provide an adequate ground to
eliminate the potential for a static spark.
Newer installations of pipeline have fiber optics installed inside the pipe.
The rupture of pipe and damage to fiber optic wires can disrupt business
over a wide area.
Leaks With Fire
Considerations at a natural gas fire should include:
Protect exposures.
Generally, let the gas burn until the supply is shut off.
If necessary, control evacuation and maintain site security.
Notify the Gas Company.
Small fires may be extinguished with dry chemical, or CO2 if necessary, to
approach a shut off valve. For larger fires, fog streams can be used to approach
any valves. Use care when placing hose streams where excavations have
ruptured a gas line. Try to keep unnecessary water out of the pit. Utility crews
may have to work in that area to stop the leak, and water could compound their
problem.
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ELECTRICAL EMERGENCIES
Power lines can come in contact with the ground as a result of storm related
activity, fire, or vehicles striking power poles. In all cases, the potential for
electrical shock/electrocution and secondary fire must be considered.
Electric Safety Awareness
Electricity will travel any conductive path it can as it seeks a ground. A direct path
to ground can occur when contact is made between something energized and a
portion of your body such as your hand, arm, head, or other body part. An indirect
path to ground will occur when you are holding something or touching an object
that is in contact with something energized. This could include tools or other
equipment you may be holding or when touching a fence, vehicle, or other object
that may be in contact with something energized. Gradient Voltage (Step and
Touch Potential) is when power lines are down, and they will energize the ground
around them. For Example: a point of ground contact could be over 7000 volts;
this voltage will lessen as it radiates out from this point. Several feet from the
initial point of contact the voltage could drop to 6000 volts. If your feet are in
areas where there is a voltage difference, you could complete the circuit and be
the source to ground. This is called “step potential.” This danger could be
indicated by a tingling sensation in your feet and serve as a warning to back away
from the area. Step potential is greater when the ground is wet. You should
remain at least 35 feet from electrical lines on the ground.
Key Points
Downed lines must always be considered energized with potentially lethal
current.
Lines can reset and become “hot” or “energized” again by manual
operation of a switch, by automatic re-closing methods (either method from
short or long distances away), by induction where a de-energized line can
become hot if it is near an energized line, or through back feed conditions.
Power line tends to have “Reel Memory” and may curl back or roll on itself
when down.
Use caution when spraying water on or around energized electrical
equipment. Hose streams conduct current! Do not spray directly into the
power lines, unless PG&E personnel have confirmed the lines are dead
and have authorized use of water on the lines. Use a fog spray at the base
of the pole. Your primary responsibility is to protect the surrounding area.
Short bursts of water are preferred methods to avoid being grounded.
Never spray water onto electrical equipment until a PG&E representative
has confirmed that the equipment is dead and has authorized the use of
water on the equipment.
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Electrical equipment is classified as:
o Energized
o De-energized (cannot be 100% guaranteed)
o Dead (confirmed by utility representatives after grounding the
lines(s).
PCB hazards: Smoke potentially fatal; avoid and contain pools of oil around
transformers.
Poor soil resistance on dry earth may not provide enough of a ground to
trip a circuit even when a conductor is laying on it.
You cannot tell the voltage of a power line by the size of the conductor.
Most overhead conductors are not insulated.
Voltage can travel through both dry and especially wet ground for
considerable distances.
Pad-mounted, overhead transformers, and vaults can explode.
Until grounded, equipment can contain electric potential, which can cause
severe injury or death.
Electricity can flow through the ground or other conductive objects, like
metal fences to point far from the scene.
Operating Around Energized Electrical Hazards
Request utility company to respond.
Consider all down wires as energized.
Place apparatus away from down lines and power poles and out from
under involved overhead lines that could fail and fall onto equipment or
personnel.
Secure the area/deny entry.
In the event of multiple lines/poles down over a large area, call additional
resources.
Down Power Lines and Vehicles
Request utility company to respond.
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Do not touch vehicle
Have occupants remain inside the vehicle
Place apparatus a safe distance away from down lines.
Fire personnel should remain at least 35 feet from power lines in contact
with the ground.
If occupants must leave the vehicle (fire or other threat to life) instruct them
to open the door, not step-out! They should jump free of the vehicle without
touching vehicle and ground at the same time; they should move away
from the vehicle shuffling their feet or hopping to avoid a voltage difference
(step potential) between their feet as they move away from the source.
Sub-Station, Transformer, Electrical Vault and Manhole Fire
Request utility company to respond.
Clear the area.
Be aware of explosion potential.
Place apparatus in a safe location away from overhead power lines.
Protect exposures.
Do not make entry until the utility representative has verified that the
electrical equipment has been de-energized. The utility representative may
have to make entry to uninvolved sections to safely de-energize the
equipment.
Power Pole Fires
Request utility company to respond.
Consider all wires and poles as “energized.”
Place apparatus away from down lines and power poles and out from
under involved overhead lines that could fail and fall onto equipment or
personnel.
Secure the area/deny entry.
Do not make any fire attack until the utility representative has verified that
the electrical equipment has been de-energized.
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Protect exposures without applying water to the powerlines/transformers.
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December 2020 Page 36
SOLAR PHOTOVOLTAIC SYSTEM SAFETY AND THE FIRE GROUND
Daytime, Daylight = Danger Shock Hazard!!
Nighttime, Darkness = Potential Shock Hazard!!
During daylight hours the Solar PV modules (panels) are energized and
present a potential electrical shock hazard. This is also true during
overcast days. Use extreme caution when working around a PV system to
minimize any potential of electrical shock.
During the nighttime/darkness, the Solar PV modules are generally not
energized and present minimal hazard from electrical shock. However,
scene lighting, low ambient light, or other artificial light sources can
generate enough voltage-current to pose a shock hazard at night. The
same safety precautions taken during the day should be taken at night.
Never walk or climb on Solar PV modules. Although the modules will likely
withstand some weight load, they still present a significant safety hazard
from breaking glass, tripping and slipping. Exposure to the cells inside of
the PV modules presents a potential electrical shock hazard.
Do not place ladders on or against the Solar PV modules/arrays.
Do not break a Solar PV module (panel) with an axe or other forcible entry
tool.
Do not attempt to remove a Solar PV module/array to perform firefighting
duties. Leave the Solar modules/arrays in place and work around the
system. If unable to work around the Solar PV array, notify the IC
immediately. Alternative ventilation tactics should be considered.
Do not cut metal conduit or wires strung between Solar PV modules or
wires coming from a series of Solar PV modules to a combiner box. This
could result in serious or fatal injury from electrical shock!
Do not attempt to remove fuses from Solar PV fuse boxes. (Not all PV
systems have fuse boxes.) Doing so will likely start a fire and presents a
significant electrical shock hazard!
Stay clear of the Solar PV modules and conduit. Utilize walkways and PV
system clearances.
Secure the Main Electric Service Panel (Main Circuit Breaker Box) for the
building.
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December 2020 Page 37
Securing the main electric power coming into the building from PG&E will only
shut down power inside the building and does not stop the PV modules from
producing DC power when sunlight or a light source is present. An electric shock
hazard still exists from the array to the DC side of the solar inverter.
Firefighter Safety Around Solar Photovoltaic Systems
Background
This section will help Firefighter awareness and safety when working around Solar
Photovoltaic systems (PV) at an emergency or fire scene. It will provide
firefighters with a fundamental understanding of Solar Photovoltaic systems and
identifying PV installations.
A fundamental understanding of PV systems includes, basic knowledge of PV
components, how PV systems operate, how to safely secure a PV system, and
how to safely perform firefighting operations, such as fire attack and ventilation at
an emergency or fire scene with a PV system.
Solar Systems: “Knowing The Difference”
While some people might think that all solar technology is the same, there are
very distinct differences between the three common types of solar system
technology on the market today. This section will identify the differences between
Solar Photovoltaic, (referred to as PV or Solar Electric), Solar Thermal (Water-
Heating) and Solar PVT (also known as cogeneration or combined systems).
Firefighters will learn common terminology, general function, solar components,
and potential hazards for each system.
Solar Photovoltaic
Solar Photovoltaic (PV) systems are used in both residential and commercial
(Figure 2 & 3) applications and produce DC electricity that is converted, using an
inverter, to AC electric power for use by the consumer. Roof mounted PV
systems are the most common and are generally visible from the street. PV
systems can also be integrated into building materials, such as roofing tiles,
awnings or overhead covers for parking lots and other structures.
PV system components include cells, modules (aka panels), electrical conduit,
and DC to AC inverter(s). The number of PV modules per system will vary
according to the total kilowatt size design of the system. Potential hazards for PV
systems include electric shock, limited or difficult roof access/egress, tripping,
slipping, falling, increased roof loads, hazardous materials, and battery hazards.
Any of these hazards emphasize the need for constant awareness and adherence
to safety procedures to prevent serious firefighter injury or death.
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Solar PV Modules wired in series
are referred to as Solar Arrays.
The presence of a Solar PV
system on this peaked roof may
not be immediately noticeable
from the street. Be prepared to
change tactics if roof operations
are hindered by the presence of
a PV system. Access and
egress become immediate
concerns. Do not place ladders
on, or break, PV modules!
Metal electrical conduit leaving
Solar Modules and penetrating
the roof can help identify Solar
Electric versus Solar Thermal
Figure 17 - Solar PV System
Solar Thermal
Solar Thermal systems (Figure 4, 5) are used to harness the solar thermal
properties of the sun to heat water and DO NOT produce electricity. Solar
Thermal systems are generally roof mounted and, range between 4-6 collectors
(panels), and cover a much smaller rooftop area than Solar PV.
Thermal system components consist of collectors with pipe to heat water, heat
exchangers water pipes, usually copper, pressure relief vents, and storage tanks.
The potential hazards related to thermal systems are increased dead load weight
on the roof and thermal burns from hot water that can be as hot as 180 F if the
panels or pipes are breeched.
A Solar Thermal system can be identified by noticeable air vents, and/or the
copper pipes (Figure 4 & 5) running between the panels and down through the
roof to the hot water storage tanks. Newer solar Thermal systems (Figure 4) can
be difficult to identify from the street.
This Solar Thermal system can be identified
from the street by the pressure relief vent (#1
arrow at left) sticking up above the array and
the copper pipe wrapped with insulation (#2
arrow at left) leaving the array. Solar Thermal
systems do not present an immediate risk to
firefighters.
Figure 18 - Solar Thermal Heating System
#1
#2
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December 2020 Page 39
This Solar Thermal system may be difficult to
identify from street level. The copper pipe
wrapped in insulation (highlighted by the red
circle at left) leaving the bottom of the
Thermal panel is the main indicator to identify
the system as solar Thermal versus
Photovoltaic. Solar Thermal systems do not
present an immediate risk to firefighters as
there is no hazard of electrical shock.
Figure 19 - Large Solar Thermal System
Solar Co-Generation
Solar PVT modules are designed to incorporate both Solar PV and Solar Thermal
into the same system. This type of system is referred to as co-generation. Solar
Photovoltaic/Thermal Co-generation (PVT) systems can generate DC electricity,
solar thermal for heating water, or thermal heating of air used to heat a building.
A PVT system covers about the same amount of roof top area as a single PV
system. The number of PV modules is dependent on the total kilowatt size of the
system and are generally mounted on roof tops.
The potential hazards with Solar PVT are the same as thermal and single PV
systems. The main hazard is electrical shock. These systems should be treated
with the same caution as Solar PV.
Identifying PVT systems should not be difficult. At first glance the system will
have the same appearance as PV. The only discernable difference will be the
Solar Thermal panels or heat “tubes” for heating air incorporated into the system,
which are generally positioned at the top of the array; however, other design
configurations exist (Figure 6 & 7).
This Solar PVT Co-generation system may
look like a Solar PV system from street
level. A tip for identifying Solar PVT
systems from the ground will be to look for
electrical conduit and PVC piping leaving
the same array. The immediate risk to
firefighters from Solar PVT systems is
electrical shock. Do not walk on, ladder, or
break solar modules! Arrow #1 to the left is
the PV module.
Arrow #2 to the left is the Thermal
component for heating water.
#1
#2
Fresno Fire Department
December 2020 Page 40
Figure 20 - Solar Co-Generation PVT System; Solar Module Combined with Thermal
Components
The Solar PVT Co-generation system at left
has Solar PV (#1), Solar Thermal for heating
water (#2) and harnesses heated air to heat
the building (#3). This type of co- generation
system will be easier to identify because of
the apparent air duct (#3) used to carry the
heat into the building. The PVC for water
heating component is hidden by the sheet
metal for the duct work. The PV electrical
conduit is also obvious when looking at the
system. Again, the immediate danger to
firefighters for this Solar PVT system is
electrical shock.
Figure 21 - Solar Co-Generation System. Solar PV and Thermal Combined. This system
will generate DC electricity and harness thermal energy to heat water and the building.
The integrated Solar PVT Co-generation
system at left has a row of Solar Thermal, to
heat water, on the top (#1) and three rows of
Solar PV (#2) on the bottom. From street level,
this Solar PVT installation may appear to be a
Photovoltaic system only. There are no pipes
or metal conduit visible from the street since
the system is integrated into the roof system.
Firefighters should notify the IC immediately
and take the appropriate steps to make the
system safe to work around. Do not ladder,
walk on, or break solar PV modules.
Figure 22 - Residential Solar PVT Co-Generation Installation
#1
#2
#1
#2
#3
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December 2020 Page 41
SOLAR PV SYSTEM COMPONENTS
This section will briefly identify and discuss PV components such as a PV cell, PV
module/array, inverters, AC and DC disconnects electrical conduit, system
labeling, and solar battery storage. Firefighters with this basic knowledge will be
able to identify PV components and learn the appropriate steps to safely secure
and work around a PV system quickly and confidently.
Photovoltaic Cell
A Photovoltaic cell is the smallest part of a PV system. However, the PV cell is
the most important part in terms of gathering solar energy produced by the sun
(photons). There are two basic types of Photovoltaic semi-conductor cells: silicon
and amorphous silicon. In most cases, the semi-conductor silicon is
approximately 1/100th of an-inch in thickness.
The basic function of a PV cell is to collect photons from the sun to energize and
force electrons from a negative layer to a positive layer in the PV cell. The
process of harnessing photons and forcing electrons from the negative to positive
layers generates around. 5 volts of solar energy per PV cell. Generally, semi-
conductor cells are cut and cast together into a thin multi-crystalline construction,
then fused and sandwiched inside a PV module. A PV module has many cells
that work together to generate solar energy.
Module/Array
Solar PV modules (also known as panels) are designed to harness DC electricity
from sunlight. A module has no moving parts and is weatherproof. Photovoltaic
modules consist of numerous PV cells wired together, enclosed in an aluminum
frame, and covered with tempered glass. Although the modules can range in
size, typically each module is 30” wide X 50” long, weighs between 30 to 50
pounds, and consists of 50 to 72 semi-conductor cells. Solar PV modules are
generally rated between 125 to 300 watts and can produce 20 to 50 volts of DC
power. Solar PV modules are normally grouped and wired in series and parallel
to increase voltage and amperage. When PV modules are grouped and wired
together, the group of modules is referred to as a PV array.
Residential PV arrays can have a total number of modules ranging from 15 to 40,
depending on the electrical needs and design of the home. A typical residential
PV system is 3 to 4 kilowatts and can produce between 120 to 600 volts DC at
currents from 5 to 9 amps during daylight hours depending on the intensity of
sunlight. With optimal sun exposure, a PV array can generate between 2,000 to
5,000 watts, or 2 to 5 kilowatt hours of DC power daily. Commercial PV systems
vary widely.
From a safety perspective, what does all this discussion of voltage and amperage
mean? Simply stated, the current (amperage) is what causes damage/injury to a
person’s body; the voltage is what drives the current through the body. The
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voltage and amperage identified above is more than enough, if contact or
exposure to the DC electrical source is made, to cause serious injury or death
from electrical shock.
Figure 23 - Solar Photovoltaic
Module
Figure 24 - Back of PV Module Showing the
Connection
Photovoltaic Inverters And Disconnects
Solar PV system inverters and disconnects are critical PV components.
Understanding the function of these components will assist Firefighters to know
where the potential dangers exist and how to isolate and shut down power to the
inverter as well as to the building. Shutting down and securing electrical utilities
for a building with a PV system is a top priority at an emergency or fire scene to
maintain a safe working environment for Firefighters.
Inverters
Typical household fixtures and appliances utilize AC power to operate. Since PV
arrays generate DC power, it must be converted to AC power before it can be
used by the consumer. An inverter converts the DC electricity from the PV array
to AC electricity which is fed into the Main Electrical Service Panel (Circuit
Breakers) for the building.
There are a variety of inverter styles and sizes. The two types of inverters used
for PV installations are system inverters and micro-inverters.
System inverters (also referred to as String inverters) are the traditional and most
common type of inverter used for solar PV systems to date. PV system inverters
are rated and designed to receive a specific amount of DC voltage from multiple
PV modules in the array and convert that power to AC electricity. A Solar PV
system may require one or more inverters depending on the total kilowatt per hour
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design of the system, which determines the potential amount of DC voltage
generated by the array.
System inverters are generally large and can be located inside and/or outside of a
building depending on available space. To operate and convert DC power to AC
power, system inverters require a dedicated AC electrical circuit wired from the
Main Electrical Service Panel. The dedicated AC circuit for the inverter(s) is a
built-in safety design to prevent the potential of electrical power being back fed
into the PG&E utility grid in the event of a power outage.
The dedicated circuit for the inverter(s) also provides Firefighters with the
ability to quickly isolate converted AC electricity coming into the building
from the inverter(s) by shutting down and securing all the circuit breakers
located at the Main Electrical Service Panel. However, this means that DC
electricity is still present in the electrical lines and conduit from the PV
modules/array down to the DC line side of the inverter(s).
Residentially installed system inverters.
The inverters can be located inside or
outside of the building. Inverters require
a dedicated AC circuit to convert the DC
electricity into usable AC power.
Securing electrical power at the Main
Electrical Service Panel will shut down
the inverters. During daylight hours, DC
power is still being generated from the
Solar PV array to the DC disconnect or
the DC side of the inverter
Figure 25 - Residential System Inverters Along with AC and DC Disconnects
Securing the Main Circuit Breaker at the Main
Electrical Service Panel will shut down the
inverters for residential and commercial PV
systems.
To prevent equipment used during firefighting
operations in commercial buildings with PV
systems from being accidentally shut down,
such as HVAC, consult with the IC or building
engineers before securing the circuit
breakers in the off position at the Main
Electrical Service Panel.
Figure 26 - Multiple System Inverters for a Large Commercial PV System
Junction Box
DC power disconnect switch
AC power disconnect switch.
DC power
disconnect
switch
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Micro-inverters are single inverters built into and/or secured on, or adjacent to,
each individual PV module. This type of inverter provides what is referred to as
“Module Level Control”, which optimizes the DC voltage levels by converting DC
electricity to AC electricity at each individual module in the array. After the
individual Micro-inverters have converted DC voltage at each module, the
converted AC electricity is fed through ordinary AC electrical circuit wiring to the
Main Electrical Service Panel for use by the consumer. Micro-inverters can be
used on residential and/or commercial solar PV installations.
PV systems that use micro-inverters significantly improve system efficiency and
provide a higher level of PV safety for Firefighters. Like string inverters, micro-
inverters require a dedicated AC circuit wired from the Main Electrical Service
Panel to operate. When power to the building is shut down at the Main Electrical
Service Panel, AC power wired to each micro-inverter is also shut down. This
isolates and contains DC power within each individual PV module in the array and
prevent the micro-inverters from converting DC power to AC power. Firefighters
must still use extreme caution when working around the PV modules/arrays as
they may still be energized and could pose an electrical shock hazard. Avoid
breaking and/or always exposing the internal construction of PV modules to
prevent serious injury or death. The micro-inverter will be built into and/or
mounted on or adjacent to PV modules.
Figure 27 - Micro-Inverter
Disconnects
Disconnects are switchblade-type electrical components required for safety.
Usually, disconnects are mounted and wired in-line on the DC line side
(upstream) and the AC load side (downstream) of the system inverter(s).
When an electrical disconnect is located on the DC line side (upstream) of the
inverter it is called the DC power disconnect. When an electrical disconnect is
located on the AC load side (downstream) of the inverter it is called the AC power
disconnect.
The primary function of the DC and AC disconnects is to allow solar technicians to
perform routine maintenance on the inverters by isolating electrical power coming
into and out of the inverters. Shutting down the DC disconnect only secures and
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prevents DC electricity produced by PV array from entering the inverter. The DC
disconnect does not shut off DC electricity supplied from the PV array. The DC
electricity coming from the array down to the DC disconnect is still energized
during daylight.
Shutting down the AC disconnect only secures and stops converted AC electricity
coming from the inverter(s). It does not shut off AC electricity supplied from the
PG&E power grid, or any AC electrical circuits coming from the Main Electrical
Service Panel for the building.
As a general safety rule for securing PV systems at an emergency or fire scene,
firefighters should shutoff and secure all switches/disconnects that are visible and
accessible and all circuit breakers at the Main Electrical Service Panel.
Communication with the IC is critically important before and after shutting
off and securing electrical utilities.
When securing a Solar PV system,
shutoff and secure all switches /
disconnects that are visible and
accessible. If the DC and/or AC
disconnect switches are not found,
securing ALL circuit breakers at the
Main Electrical Service Panel will
shut down the inverter and stop AC
power from going into the building.
During daylight hours, DC power is
still being generated and is present
from the Solar PV array to the DC
disconnect.
Figure 28 - Residential Solar PV inverter, DC and AC disconnect junction box and Main
Electrical circuit breaker panel.
Solar PV System Labeling
Labeling of Solar PV systems, residential and commercial, can be a critical clue
for overall Firefighter safety. This critical component can easily be overlooked if
firefighters are not performing thorough size-up of an emergency or fire scene.
The danger that exists with solar PV systems is having two electrical power
sources for one building: the traditional AC electrical service provided by the
Pacific, Gas and Electric (PG&E) power grid and the secondary electrical power
source from the solar PV system.
Since solar PV systems are categorized as “Customer Side Power Generation
Equipment with Back Feed Potential,” PG&E requires that labeling on the Main
Electrical Service Panel identify the presence of a secondary power source
(Figure 29). Unfortunately, labeling for solar PV installations is not uniform or
regulated. The type and amount of warning labels throughout the PV system will
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vary depending on who installed the system, where (what city or county) the
system is installed, and how long ago the system was installed.
Various labels can be found on PV components, such as Main Electrical Service
Panels, PG&E utility meters, PV modules, electrical conduit, DC, and AC
disconnects, and other random locations. The purpose of PV labeling is to
indicate the presence of a Solar PV system on or supplying the building with solar
power.
Figure 29 - Warning label on the front of a Main Electrical Service Panel (circuit breaker).
The label in this instance clearly identifies the secondary power source is solar PV.
A bi-directional PG&E meter (Figure 30), used only for grid-tied PV systems, will
be identified with a label that states, “Meter Runs in Both Directions.” This type
of labeling is to prevent accidental back feed of electricity into the grid. Bi-
directional meters will be present on all "grid-tied" solar PV systems.
Figure 30 - Bi-directional meter labeled to indicate the presence of an
alternative power source (PV).
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Key Point: This should be a Top Priority!
Securing both AC and DC electrical power sources to the building is critical
to rendering the building as safe as possible for Firefighters. The electrical
power to the building will not be completely shut down until the Main
Circuit Breaker, located in or on the Main Electrical Service Panel for the
building is secured (shut down). If any of system disconnects are visible,
they should also be placed in the “OFF” position. Notify the IC when both
AC and DC electrical power sources to the building have been properly
secured. This should be a Top Priority!
Remember, during daylight, DC power is being generated from the PV
modules down to the DC disconnect. DC power cannot be completely shut
down unless all the PV modules are completely covered with an opaque
tarp or cover during daylight hours. During darkness, ambient light from
fire or scene lighting may generate enough power to present an electrical
shock hazard. Always use extreme caution.
Figure 31 - Label on the side of a solar PV mobile installed on the roof, provides firefighters
with a reminder of potential hazards as well as the name of the electrical contractor who
installed the system.
The warning: “Line” and “Load” sides of any disconnect switch box could still be
energized and present a shock hazard, even after the disconnect switch has been
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placed into the “OFF” position. This is generally the result of having dual power
sources and the potential for back feed of electrical power throughout the system.
Figure 32 - DC and AC power disconnect labels.
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THE PHOTOVOLTAIC SYSTEM: HOW IT WORKS!
While every building is different, PV systems are functionally the same. The
technology utilizes a basic process to produce and convert solar power for use by
both residential and commercial consumers. Each of the PV components has a
specific job; when combined with each other the PV system will harness the
highest amount of solar power possible.
This section will bring all the components together in one unit to provide a better
understanding of the technology and operation of “grid-tied” and “off-grid” PV
systems, battery back-up and storage, how daytime and nighttime light affects PV
systems, and to improve recognition of different PV designs and installations. The
differences in PV design and installation are based on individual consumer
electrical needs, how the solar electricity will be used or stored, and whether the
system will be residentially or commercially installed.
Knowing the difference between the system types determines what optional PV
components might be installed and is an important safety factor for Firefighters. A
basic knowledge of how solar PV systems work will help Firefighters understand
where the potential hazards exist and how to reduce close-call injuries or Line of
Duty Death (LODD).
Basic PV System Overview—“Grid-Tied” and Off-Grid”
The amount of DC electricity generated by a solar PV system is variable. Solar
PV systems are dependent on the atmospheric conditions and the condition of
interconnected PV components to operate correctly and at optimal efficiency. The
time of day, the amount of direct and indirect sunlight on the array, cloud cover,
shade, shadows, and the mechanical condition, location, and proper installation of
PV components are examples of factors that directly affect the overall operation
and performance of a solar PV system.
The basic function and operation of how Solar PV systems harness energy from
sunlight to produce electricity is the same; Sunlight is converted to DC electricity
by solar cells and DC electricity is converted to AC electricity using an inverter.
The only difference from one PV system to the next is design. PV system design
is divided into two categories, grid-tied and off-grid. To determine the most
suitable PV system for a specific consumer, the design is based, in part, on
individual consumer electrical needs and objectives and overall cost.
“Grid-Tied” PV Systems
The term “grid-tied” refers to alternative solar photovoltaic electrical power being
used in combination with traditional electrical power supplied by the PG&E utility
power grid. For most consumers, a grid-tied PV system is the ideal configuration.
Consumers get all the benefits of using their own solar electricity as well as the
benefits of being connected to the PG&E power grid. There are two design
styles for grid-tied PV systems, direct and battery back-up.
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A direct grid-tied system is the basic style design for grid-tied PV. Consumers do
have the option to upgrade the system with battery back-up to mitigate power
outages. The basic operation and design difference between direct grid-tied PV
and a grid-tied battery back-up system is discussed below.
Direct Grid-Tied PV Systems
The most common PV system is a direct grid-tied system. A grid-tied PV system
is connected directly to the PG&E utility power grid. This allows AC power to flow
both into and out of the building through a bi- directional meter on the Main
Electrical Service Panel. The amount of AC power being supplied into or out the
building depends on the electrical needs of building occupants and the amount of
electrical power produced by the PV system at that exact time.
When the PV system is producing adequate solar electricity, the building only
utilizes solar power. This is the PV system’s first priority. During times when the
PV system cannot produce enough solar electricity or is not producing solar
electricity at all, such as at night, the building electrical service will utilize power
from the PG&E grid.
When the PV system is producing more solar electricity than the building
occupants can use, the excess is fed back through the bi-directional meter into
the PG&E power grid.
This is known as net-metering. With net-metering, when a consumer uses
electricity from the PG&E grid, the bi-directional meter spins forward. When the
consumer-based PV system is producing excess solar electricity and feeding
power into the PG&E power grid, the bi-directional meter spins backwards. The
offset means that consumers with PV systems are receiving market rates for the
amount of electricity fed into the PG&E grid.
The downfall of direct grid-tied PV systems occurs during power outages. As
discussed earlier, PV inverters require a dedicated AC circuit to convert DC
voltage into usable AC voltage. When the PG&E grid has a power outage, the
inverter also loses power and cannot convert DC electricity into AC electricity for
the duration of the outage. This is a built-in safety design to prevent back feeding
of DC electricity through the system and into the power grid. AC electrical power
to the building will be restored after the PG&E grid power is restored. This will
occur regardless of the time of day.
**Safety Point: If the power outage occurs during daylight, the solar PV
array is still producing DC voltage. Therefore, DC electricity will be present
at the arrays and in the electrical conduit from the array to the DC voltage
side (input) of the system inverter(s). There will be no power beyond the
inverter until grid power is restored. Light from fire or scene lighting during
darkness may produce enough electricity to present a significant shock
hazard. Use caution when working around the array and electrical conduit
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always coming from the array to the inverter, whether there is a power
outage or not!
In the typical Direct "Grid-Tied" Solar Photovoltaic System, the DC electricity is
converted into AC electricity by the Inverter and then fed into the Main Electrical
Service Panel. The Main Electrical Service Panel supplies residential or
commercial buildings with AC electricity. Excess AC power not being used in the
building is fed into the PG&E power grid.
Figure 33 - Typical Direct Grid-Tied PV System
Grid-Tied PV with Battery Back-up Storage System
Grid-tied PV systems with battery backup storage offers the convenience of being
connected to the grid with the security of having uninterrupted backup power
during a PG&E grid power outage. This system design is commonly used for
buildings that have critical electrical needs. Grid-tied PV systems with battery
back-up storage operate in the same basic manner as direct grid-tied PV systems
and utilize Net Metering. The difference between the two systems is the bank of
batteries to store DC electricity for use during power outages. The DC electrical
storage is accomplished by adding components into the PV system designed to
use excess DC electricity to charge the battery bank.
Identification of battery back-up storage systems must be reported immediately to
IC to prevent accidental electrical shock. To isolate a battery back-up system,
Firefighters should be familiar with the basic functions of the additional
components, which include the following:
Charge Controller - To prevent the batteries from overcharging.
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Bank of batteries - To store accumulated DC voltage for use when there is
a power outage or no electricity is being produced, such as at night.
Stand-Alone Inverter - Inverters of this type use both AC power on a
dedicated circuit when the PG&E grid is operating, and DC power supplied
from the battery bank during a power outage, to convert DC electricity into
AC electricity. The inverter utilizes DC voltage from the batteries and
capacitors that store energy to operate during an outage. Energy in the
capacitors will discharge soon after the power to the inverters has been
isolated. A significant electrical shock hazard could always exist.
Backup Electrical Sub-Panel and Electrical Circuits – During a power
outage the AC voltage being converted by the stand-alone inverter is fed
into a backup AC electrical circuit that energizes and feeds into a backup
sub-panel before distributing power from the backup sub-panel into the
building electrical circuits. The sub-panel is a safety feature designed to
isolate electrical power during a power outage and any potential for
electricity back feeding into the PG&E grid. Backup electrical circuits are
tied into the normal electrical circuits for the building such as outlets,
lighting, and appliance circuits.
Figure 34 - Typical Grid-Tied PV System with Battery Backup Storage
“Off-Grid” PV System
A PV system that is “off-grid” or a true stand-alone PV system produces solar
electric power independent of the PG&E utility power grid. This type of system is
more commonly found in rural areas, in environmentally sensitive areas, or in
illegal activity. Most off-grid PV systems rely on DC electricity produced during
daylight to charge and store DC voltage using a large bank of batteries. The
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system components for an “off- grid” system is basically the same as a grid-tied
system with battery backup storage.
Stand-alone inverters commonly utilize power from batteries and capacitors that
store energy to convert the DC power into AC power. The capacitors hold an
electrical charge capable of producing a significant electrical shock hazard for
several minutes after power to the inverters has been disconnected. The basic
operation of off-grid PV systems is essentially the same as a grid-tied PV system.
The most distinguishable difference is the use of a backup generator as a
secondary source of electrical power when the battery bank is discharged or
depleted of DC voltage. The backup generator produces DC voltage and is tied
directly into the inverter. Backup power can be used during the night or when
there is a problem with the bank of batteries. Off-grid PV systems reaffirm the
need for Firefighters to have a standardized approach to working around solar PV
for optimal safety.
Figure 35 - Off-Grid PV System with Battery Back-up Storage and Backup
Generator as a Backup Secondary Source
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Solar PV System Recognition
Roof-Mounted PV Systems
Roof mounted systems are the most common installation design for residential
and commercial solar PV Systems throughout the industry. Roof-mounted PV
systems are a popular design because of the utilization of unused space on the
roof and optimal southern exposure to the sun. Roof-mounted systems generally
use metal racks or single anchors, specifically designed for PV modules, to
secure the array over existing roof surfaces to the sub-structure (rafters) below
the roof. Racks for PV modules can be elevated for flat roof installations or may
sit just a few-inches over the existing roofing material on a peaked roof.
Identification from the ground at street level can be difficult. Firefighters should be
able to recognize PV components to assist in recognition of a PV system.
Recognizable components from the street level include modules mounted on the
roof, PV labels on electrical components, visible electrical conduit coming from the
roof or entering the attic space, inverters, multiple disconnect switches, or a bi-
directional meter at the Main Electrical Service Panel.
Street level recognition of roof-mounted systems is not always possible due to
weather conditions, building height, flat roofs, parapet walls, and time of day.
Firefighters working on a roof should immediately communicate the presence of a
roof-mounted PV system and any hazards preventing normal operations to the IC.
Figure 36 - Roof Top Residential PV System
Ground Mounted PV Systems
Ground-mounted PV systems are not often found in urban areas. Ground-
mounted PV systems generally allow the PV array to be installed in a proper
location and angle for optimal exposure to the sun.
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Ground-mounted PV systems are generally not difficult to recognize. The
difficulties for Firefighters are the ability to identify the location of system
disconnects, location of electrical conduit, and the ability to isolate and shutdown
electrical power coming from the PV array.
Street level recognition can be difficult, and Firefighters must have a higher level
of awareness for identifying alternate PV system installations and designs located
in their geographical response area.
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EFFECTS OF LIGHT ON PV SYSTEMS
Daylight
During daylight, a Solar PV system will provide some, or all, of the building’s
electrical needs, residential or commercial, depending on the amount of electricity
that appliances or machinery inside the building require at the time. If the Solar
PV system is not providing all the power needs, the balance of power needed is
automatically provided directly from the PG&E power grid. On days when sunlight
is intense, the PV system will generally produce more power than needed. The
excess power is automatically fed into the PG&E power grid and a credit is
recorded on the bi-directional meter (Net Metering).
The amount of power being generated at any time during the day will still
present a significant electrical shock hazard that could result in permanent
injury and/or death, regardless of the intensity of the light on the array.
Firefighters should never assume that low levels of daylight or less intense
sunlight due to clouds or shade will stop a PV system from producing
electricity.
Nighttime
Generally, at night, solar PV systems will not produce electricity. However, low
ambient lighting, artificial light from scene lighting, light from fire, or street lighting
may be able to generate enough light for solar cells to produce DC electric power
that could present an electrical shock hazard during hours of darkness.
This has been documented by Underwriter Laboratories (UL) during experiments
with solar PV and the effects of light from sources other than the sun.
The potential to create solar electricity from light sources other than the sun
depends on several conditions: intensity, location, and distance of the light source
from the PV modules.
In the recent past, the fire service considered a solar PV system safe to work
around at night or during darkness because it was assumed that the systems do
not generate enough DC electricity to be harmful. However, the potential for a PV
system to generate enough DC electricity to present an electrical shock hazard,
indicated by UL studies, has prompted a change for overall Firefighter safety
related to solar PV during periods of darkness at a working fire or an emergency
scene.
Even though it is nearly impossible to know if the PV system is producing enough
DC electricity to present a hazard, Firefighters should consider the potential for
electrical shock and take steps during hours of darkness to render the PV system
as safe as possible. Remember, during the night, a “grid-tied” PV system is not
producing enough DC power and electricity from the PG&E power grid is
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provided. Firefighters should also be aware of the potential for “grid-tied” systems
to have battery back-up.
**Safety Point: For overall safety, ALL PV systems should be isolated at any
time of day or night, before working around the system.
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PV SYSTEM HAZARDS
The general hazards that exist for solar PV on residential or commercial
structures are not strictly specific to PV technology. The same hazards exist with
traditional electrical systems. However, when the integrity of a PV system
component or protective covering is compromised or damaged due to fire or other
destructive causes, the system always presents significant hazards and unique
safety concerns for Firefighters.
Hazardous Materials Inhalation Hazard
Hazardous materials such as silicon, boron, phosphorus, cadmium, tellurium,
arsenic, and gallium, are used in the construction of PV modules and
components. In PV modules these materials are sealed between the top layer of
glass and the plastic backing of the module, and then are encased in an
aluminum frame.
When the PV system is operating under normal conditions, these chemicals do
not constitute a hazard. However, a fire may expose the hazardous chemicals to
direct flame and/or significant heat.
Wear all PPE during fire attack and overhaul operations. All chemicals listed
above are considered toxic under fire conditions; some have a significant
increased cancer risk with exposure.
PV System Battery Hazard
Banks of batteries storing electricity are generally arranged in a line and are
connected to each other. There are two types of batteries used as electrical
storage for PV systems, lead acid and lithium ion.
Both battery types are stable under normal circumstances. Firefighters working
around battery banks during fire attack and overhaul operations must utilize
proper PPE, including breathing apparatus.
Firefighters should isolate the bank of batteries from the PV system, if needed. If
the PV system is disconnected from the batteries, the bank of batteries
themselves still has potential for electrical shock. Firefighter should never attempt
to cut into or attempt to damage the batteries under any circumstance. If the
batteries are punctured by a conductive object, such as halligan tool, the object
may become energized. Firefighters working around or adjacent to the battery
storage areas should only use flashlights and equipment approved for CLASS 1
atmospheres.
When Firefighters determine that a PV system is using a battery bank to store
electricity, the IC should be notified about the hazard and the location of the
batteries in the building.
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INCIDENT PRIORITIES AND TACTICAL CONSIDERATIONS
Fire and emergency incidents for residential and commercial buildings have a
basic and standardized approach. However, fire and/or emergency incidents
involving solar PV systems require special considerations. The special
considerations are a result of the inherent and associated hazards of PV systems
and are necessary to ensure Firefighter health and safety and to accomplish fire
control in a safe and efficient manner. Incident Priorities and Tactical
Considerations for solar PV systems during fire and/or emergency operations are
outlined below.
Communications
All findings during the initial and on-going size-up and any actions taken
need to be communicated to the Incident Commander (IC).
Incident size-up and identification of PV system and components
o Solar PV array visible from the street upon approach and/or arrival.
o System inverter(s) visible or evident anywhere on the building.
o PV labeling identifying the presence of a PV system.
o DC or AC disconnects visible and/or accessible.
o Visible electrical conduit penetrating the attic space or near the main
panel.
Securing Utilities
Securing Utilities is a top priority for incidents involving a PV system to
maintain a safe work environment for Firefighters.
Locate Main Electrical Service Panel.
o Shut off Main Breaker inside the Main Electrical Service Panel.
This will shut down the AC power at the Main Electrical
Service Panel and AC power going into the building.
Shutting off the Main Breaker will also de-energize the AC
power used by the inverter to convert DC into AC power.
o If in doubt which is the Main Breaker, shut-off all circuit breakers
inside the Main Electrical Service Panel.
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Use caution for large commercial and high-rise buildings.
Electrical power might still be needed to power HVAC
systems and elevators.
Consult with building engineers (if applicable) to isolate
the PV system ONLY!
Consider using Lock-out/Tag-out system to secure PV system.
Locate and isolate the PV system and battery bank (if applicable).
o Locate PV Inverter(s) and disconnects.
Shut disconnects into the “OFF” position.
o Locate PV system batteries (if applicable).
Shut disconnects for battery bank into the “OFF” position.
o Locate and shut off all visible disconnects or switches for the PV
system.
Near Bi-directional Electric Meter.
Near the inverters.
Switch-gear on the roof.
Roof top disconnects.
o Notify the IC when the utilities and PV system have been secured.
Fire Attack Considerations
Coordination of fire attack and ventilation
o Fire attack could be delayed or hindered due to difficulties with
completing ventilation.
o Advancing hose lines could be delayed due to securing PV and
building utilities.
Be aware of energized PV system components inside the building.
Notify the IC if wires and conduit inside the building is located.
o Avoid contact with conduit or wires if possible.
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Attempt to avoid directing hose streams directly onto energized PV system
components.
If possible and indicated, use Dry Chemical Extinguishers or CO2
Extinguishers around PV components.
If water is used PG&E recommends Fog Nozzle at a 30-degree pattern at
100 psi minimum at the tip and at least 33 feet from the energized source.
UL experiments indicate that using a solid stream, smooth bore nozzle at
50 psi at the tip and at least 20 feet from the energized source is
considered safe up to 1000 volts. PV systems have a maximum allowable
voltage of 600 volts.
Difficulties with fire attack must be communicated to the IC.
Ventilation Considerations
Early recognition of the PV modules and identification of difficulties with
completing ventilation objective is key for Firefighter safety.
Identify safe access and egress to the roof if possible.
PV modules/array on the roof may affect ground or aerial ladder
placement.
Do not cut through any conduit or wires to complete ventilation due to the
potential for electrical shock.
Do not break PV modules with an axe or attempt to remove PV modules to
ventilate due to electrical shock hazard.
If vertical ventilation cannot be accomplished because the PV system does
not provide firefighters with clearance, consider changing ventilation
tactics, and notify the IC immediately.
If a PV module is involved in fire, it does not present a hazard to utilize a
hose line to extinguish the fire if all recommendations for PPE, SCBA, and
use of water streams are followed.
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DEFINITIONS
AC Disconnect - The AC disconnect is the AC power shutoff. The AC disconnect
is in line between the inverter and the Main Electrical Distribution Panel for the
building.
AC Voltage - AC stands for “Alternating Current.” This means that the voltage is
not constant and changes polarity (reversing positive and negative) or direction
over time. AC is the type of electricity that is found in your home and delivered by
PG&E. AC voltage in the home is commonly 110 volts for most ordinary
electronics. Larger appliances, such as a clothes dryer, are usually 220 volts.
Appliance Valve - A hand-operated valve on the pipe connecting a gas appliance
to a customer house line. Turning this valve will shut off gas to the appliance.
Array - A group of modules wired together in series to generate a greater amount
of DC voltage. Arrays can be mounted in various locations on a building or
adjacent to a building. Arrays will vary total size.
Backing Nut - The nut on a stopcock, located opposite the tang. This nut should
never be loosened except in an emergency.
Combiner Box - The combiner box is used as a collection point for the many
wires from the modules that are wired together (combined). The wires coming
into the combiner box will vary in number depending on the number of PV
modules in the array. Wires leaving the combiner box will generally be encased in
electrical conduit on the way to the DC disconnect before the inverter(s).
Core - The cylinder inside a stopcock that allows or blocks the flow of gas. It is
connected to the tang and rotated by turning the tang. It is held in place by the
backing nut.
Curb Marker - The letter "G" painted or chiseled on a curb. It marks where a
service line passes under the curb. It, also, indicates on which side of a structure
a meter is located.
Curb Vault - A small concrete compartment containing an emergency gas shutoff
valve that is usually located under a sidewalk or parkway. It is accessible through
a removable lid.
Customer House Line - Gas pipe within a structure that is usually running inside
walls and floors. It is the line from the meter to which appliances are connected.
DC Disconnect - The DC disconnect is the DC power shutoff. The DC
disconnect is in line between the solar arrays and the inverter
DC Voltage - DC stands for “Direct Current.” This means that the voltage or
current maintains constant polarity or direction over time. DC is the kind of
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electricity made by a battery (with definite positive and negative terminals), or the
kind of charge generated by rubbing certain types of materials against each other.
DC electricity must be converted to AC electricity to be used for household
appliances and electrical circuits.
Distribution Pipeline System - Part of the system that carries gas from large
transmission pipelines to individual customers, which is sometimes referred to as
a gas main. Normally, the pressure in these mains is between 40 and 60 psi.
Emergency Shutoff Valve - A gate valve with a wheel type handle located in a
curb vault at a sidewalk or parkway. Turning the handle clockwise will shut off the
gas to the structure. These valves are usually located at public assembly
buildings, schools, churches, hospitals, and theaters.
Flash Point - The temperature at which ignition or explosion will occur. For
natural gas it is 1100 degrees Fahrenheit. However, natural gas will only ignite
when its concentration in air is between four and 14 percent.
Grid Tied - A solar PV system that can feed electrical power into the PG&E utility
power grid.
High Pressure Leak - A leak in either a transmission line or distribution main.
Only the Gas Company has the capability of shutting down these leaks.
Hydrogen Sulfide - A toxic gas that, on rare occasions, is present in leaks at
natural gas compressor stations or at underground storage fields.
Inverter - The inverter converts incoming solar DC voltage from the modules to
AC voltage before going to the building circuit breaker panel.
Line - In relation to a given switch or device, line refers to wires or voltage being
"supplied" to it from "upstream" or from the direction of the Main Electrical Service
Panel or power source.
Load - In relation to a given switch or device, load refers to wires (or terminals)
that are "downstream" from or controlled by the switch or device. Another use of
the term "load" is to refer to the energy "user(s)" along the circuit's path, such as
a light or appliance. By providing resistance, these items limit current and, in the
process, do useful things with that current.
Low Pressure Leak - A leak in a customer house line, on the outlet side of the
meter, approximately 1/3 psi. Using a redwood plug, or even by pressing a finger
against the leak, can temporarily stop such leaks.
Main - Gas pipe running under a street or parkway; part of the distribution system.
Management Representative - The Gas Company sends a liaison to the scene
of a major gas emergency that remains until the hazard is eliminated. This person
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will maintain communication with The Gas Company, the Fire Department, the
Police Department, and the public.
Master Meter - A meter that serves more than one unit, e. g., an apartment
complex or mobile home park.
Migrating Gas - Gas from an underground leak. It may travel along pipes and
rise through ground openings, or it may become concentrated in sewers and
spaces under structures.
Meter Set Assembly (MSA) - This is the term The Gas Company uses to
describe the meter and all the surrounding fittings, including the pressure
regulator, the riser pipe, and the stopcock.
Module - A single aluminum-framed solar panel covered with tempered glass.
Modules are sometimes referred to as panels.
Module Level Control - Solar PV components designed to improve overall PV
system efficiency and safety. Increased safety is achieved by improving the
ability to isolate a PV system to prevent accidental electrical shock.
Multiple Meters (Headers) - A row of meters connected to a common riser. Each
meter is connected to a separate customer house line. These meters can be
turned off together or individually.
Natural Gas Emergency - An incident involving a natural gas leak from a
damaged pipeline or appliance.
Net Metering - Agreement between the utility company and the PV system owner
to “bank” excess power produced by the PV system and to feed it into the utility
power grid. The excess power used by the utility company is offset when the PV
system owner needs to use power from the utility power grid when the PV system
is not producing power.
Non-Sparking Mallet - The type of mallet that should be used to drive a plug into
the end of a broken pipe. Wooden, rubber, plastic or brass mallets will not cause
an igniting spark if they strike the pipe.
Odorant - Substances known as Mercapitan and Thiophene. They have a
distinct odor that is added to natural gas. Since natural gas is odorless, this
substance makes it possible to identify the presence of a leak.
Off Grid - A PV system not connected to the utility power grid. This type of
system is otherwise known as a “stand-alone” system.
Photovoltaic Cell - A semi-conductor device designed to convert solar energy,
produce by the sun, into DC electric power.
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Plastic Pipe - An increasing number of gas distribution pipelines are made of
plastic. Gas escaping from a break in these pipes can create a static electric
charge. Fogging the pipe with wet water reduces this hazard.
PV - PV stands for Photovoltaic. Solar Photovoltaic Systems generate DC
electricity from sunlight (photons).
PVT - Solar Photovoltaic and Thermal Systems generate DC electricity and solar
thermal heating for water co-generated from sunlight.
Redwood Plug - Wooden plug that is driven into a broken, low-pressure, pipe to
stop the flow of gas.
Regulator - A fixture shaped like a disc installed in the gas line, above the riser
and before the meter. It reduces gas pressure to approximately 1/3 psi.
Rerouting - When there is a leak in a high-pressure pipeline, The Gas Company
will shift the flow of gas into an alternate line. Because of the large amount of gas
involved, it can take several hours for the gas to be purged from the damaged
line.
Riser - A vertical pipe that carries natural gas from an underground service main
to the MSA. It is the pipe on which the stopcock is located.
Service Line - The gas line that runs under a customer's property from the main,
to the riser.
Stopcock - A gas shutoff valve located on the riser; occasionally referred to as a
"service shutoff valve".
Tang - The grip on the stopcock. When its long side is turned crosswise to the
riser, the flow of gas is stopped; if square, a raised line on the tang is turned
crosswise when the flow of gas is stopped.
Transmission Pipeline System - Large size pipeline, up to 36-inches in
diameter, used to move gas over long distances to local distribution areas.
Pressure in such a pipeline can be as high as 1,000 psi
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REFERENCES
Backstrom, Robert and Dini, David A. “Firefighter Safety and Photovoltaic
Installations Research Project” Underwriters Laboratories Incorporated, Northbrook,
IL. November 29, 2011 http://www. UL. com/
Excerpt from North Carolina, OFSM, “Module II: Basic Electrical Concepts and
Hazards” “Personnel Protection Devices for Specific Applications, Electric
Power Research Institute, Project” 6850-02, Final Report, October 1999, prepared by
Underwriters Laboratories Incorporated
CAL FIRE-Office of the State Fire Marshal, “Solar Photovoltaic Installation Guideline”
April 22, 2008 and “Fire Operations for Photovoltaic Emergencies” November 2010,
http://www. osfm. fire. ca. gov/training/pdf/Photovoltaics/
Paiss, Matt, Fire Captain San Jose Fire Department, video and seminar “Photovoltaic
Systems and Firefighter Safety”, 2009, 2010 contributor to California OFSM
“Photovoltaic Guidelines” and “Fire Operations for Photovoltaic Emergencies”,
Photovoltaic consultant 2011
Enphase Energy Company, “PV Systems and Fire Safety” http://www. enphase. com/
, 1-877-797-4743, 1420 N. Mcdowell Blvd, Petaluma, CA, 94954
San Francisco Fire Department 698—2nd Street San Francisco, CA 94107
Dini, David A, Research Engineer, Electrical Hazard Group, Corporate Research,
Underwriters Laboratory incorporated, “ Leakage Current Research Document,”
gathered references with excerpts from the following sources; “Electrical Shock,” an
educational presentation of Underwriters Laboratories Inc. , prepared by Walter
Skuggevig, 1991; “Personnel Protection Devices for Specific Applications, Electric
Power Research Institute, Project 6850-02, Final Report”, October 1999, prepared by
Underwriters Laboratories Inc. ; IEC-60479-1, “Effects of Current on Human Beings
and Livestock – Part 1: General aspects”, International Electrotechnical Commission,
4th ed. , 2005-07; “Electric Current Through the Human Body”, Walter Skuggevig,
Underwriters Laboratories Inc. (undated publication); “Standard for Safety for
Portable Spray Hose Nozzles for Fire-Protection Service”, UL401. 4th ed.
Underwriters Laboratories Inc., 2004; “Fire Protection Handbook” 20th ed., Quincy,
MA: National Fire Protection Association, 2008; G. W. N. Fitzgerald, “Fire Fighting
Near Live Electrical Apparatus,” Ontario Hydro Research News, April – June 1959,
vol. 11, no. 2;