PV Systems and Firefighter Safety
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Firefighters have a dangerous job. Running into a burning building instead of out of it might seem to be the height of risky behavior. In reality, though, what appears from the street to be a heroic and reckless assault on the flames is really an intricately orchestrated exercise in risk management.
Risk management includes preplanning, training in both the classroom and in the field and the complex coordination of trained personnel at an incident. The most common cause of firefighter injuries and deaths is simply the unknown. For example, what is inside those metal drums in the burning garage? Is it flammable, toxic or explosive? If the answer is “We don’t know,” fire commanders give orders to fight the fire from a safe distance or even to let it burn.
Unfortunately, PV systems fall into that unknown category for fire departments that are encountering them for the first time. With the rapid growth of utility-interactive PV systems in urban and suburban settings, such encounters are becoming more and more common.
As the local PV installer, you can significantly improve the safety of firefighters in your district (and maybe even the attitude of your local government toward PV) by educating your local fire department. Do not wait until after a fire in a PV-equipped structure to get the word out. Instead, be proactive and educate your local firefighters and their commanders to take PV systems from unknown to “Okay, we understand this.”
At the Scene
If you understand what firefighters do at an incident besides spray water, you will be better prepared to answer their questions during your outreach sessions. En route to the incident, firefighters consult “run books,” either on paper or on a laptop, that contain details about the destination. Information about elderly or infirm residents with special medical needs, the nearest hydrants or other water sources, turnarounds for fire apparatus, structural details, roof type and even mean dogs might be on file. Upon arrival, firefighters perform a 360° walk-around of the structure to identify other possible hazards not listed in the run book, and team assignments are made. One team may be in charge of the water supply, one might prepare to access the roof, one may enter the structure with a rapid intervention team standing by in case the interior attack team gets into trouble.
As teams prepare for their tasks, the local utility is usually called to disconnect electric service at the pole, as overhead power lines and aluminum fire ladders do not mix. If utility line workers are slow to arrive, firefighters may pull the meter outside the structure to disconnect it from the grid.
Firefighters frequently need roof access during an incident. Chimney fires are common, and embers from anything burning in the neighborhood— even a next-door BBQ—can easily lodge on a roof. During a serious structure fire, firefighters may need to cut holes in the roof over the fire for vertical ventilation—a carefully timed procedure in which firefighters inside chase superheated gases out of a room with a water fog just as holes open up from above, cut by firefighters on the roof wielding demolition tools and chain saws.
After the fire is out, the mop-up phase begins. Every nook and cranny is checked for heat by hand or with a thermal imaging camera and opened up for more water if needed. Drywall and paneling are pulled down to check for hidden fire, and all the ashes and debris are stirred and watered to eliminate hot spots.
How PV Systems Can Surprise Firefighters
Consider the myriad hazards that firefighters face in a PV-equipped building if they do not understand the technology.
If their run book does not contain information about the PV system, firefighters waste valuable time trying to identify those “funny things on the roof ” and the hazards they might pose. Do they produce electricity, hot air or hot water? If hot water, what is the heat exchange medium? If electricity, are there rooftop disconnects, and where are they located?
Firefighters unfamiliar with grid-tied systems with battery backup might assume that all interior mains circuits are dead after the meter is pulled, while in fact they might still be live and powered from an inverter and battery bank. This is not much different from an auto-start backup generator with an automatic transfer switch, which firefighters are already familiar with. However, usually they can hear the backup generator and realize that it needs to be shut down.
The team tasked for roof access and vertical ventilation might not know that the PV module strings on the roof are very fragile and can be energized up to 600 Vdc anytime the sun is shining. Accidentally breaching any module with an aluminum roof ladder or while cutting into the modules with a demolition saw can expose a firefighter to the full voltage potential of the entire series module string.
Firefighters tend to rely on “hot stick” voltage-detector wands to reveal dangerous voltage potential, but they may not know that hot sticks do not pick up dc voltages.
Teams may not be aware that PV source circuits can have multiple disconnects in different locations—some might be outdoors, others indoors. If there is no system map available, nobody knows what circuits are live or dead at any given time.
Mop-up after a fire is very dangerous, and PV systems can add complications. Consider a midnight attic fire, underneath a PV array. Was the insulation on PV source wires compromised inside the metal conduit in the attic? If so, when the sun comes up, PV source circuits (and even the conduit itself, if shorted to a hot wire) can become live and shock firefighters who are trying to mop up.