The global solar industry is advancing at a rapid pace, which is promising news for this market and for the continued push for clean, renewable energy sources. This pace also creates the need for new maintenance procedures, increased consumer education and more rigorous training, particularly around new firefighting tactics in the unfortunate event that a structure with a photovoltaic (PV) system catches on fire.

In the past several years, PV system technology has also seen rapid advancement. PV systems produce more energy and incorporate lower cost materials and, as such, they are more accessible to the average homeowner, building/business owners and other independent power producers.

PV’s inherent risk

Innovation in PV modules has allowed for the increase in absorption rates of sunlight and the subsequent conversion to usable energy. Panels are much more efficient, and therefore, may operate at higher temperatures than their predecessors. The increased operating temperatures mean that PV modules are not placed flush against a roof, but may now be placed four to seven inches above a roof deck. This air gap can cause any fire between the PV panel and the roof to be much more intense than a traditional roof fire.

The increased use of PV panels adds to the complexity of the traditional firefighter tactics for suppression, ventilation and overhaul more complex. Though the electrical and fire hazards associated with electrical generation and distribution systems are well-known, PV systems present unique safety considerations. In an effort to provide more knowledge about the risk of mitigating such PV-related fires, and support the widest adoption of solar as a viable, renewable source of energy.

Fire safety tests

To gain a greater understanding of such technologies, UL scientists constructed a functioning PV array to serve as a test fixture under the US Department of Homeland Security Assistance to Firefighters Grant, Fire Prevention and Safety Research Program. Existing fire test fixtures located at the Delaware County Emergency Services Training Center were modified to construct full-scale representations of roof-mounted PV systems. The main test array consisted of 26 PV framed modules rated 230 Watts each (5980 W total rated power).

UL discovered seven new findings regarding roof-mounted photovoltaic systems that impact firefighter safety

Multiple experiments were conducted to investigate the efficacy of power-isolation techniques and the potential hazards from contact of typical firefighter tools with live electrical PV components. As a result, UL discovered new findings that impact firefighter safety:

• Turning off an array is not as simple as opening a disconnect switch. Depending on the individual system, multiple circuits may be wired together to a common point such as a combiner box. All circuits supplying power to this point must be interrupted in order to partially de-energize the system. As long as the array is illuminated, parts of the system will remain energized. Unlike a typical electrical or gas utility, a PV array has no single point of disconnect.

• Overlaid tarps offer varying degrees of effectiveness to interrupt the generation of power from a PV array, independent of cost. Heavy, densely woven fabric and dark plastic films reduce the electrical output from the PV to near zero. If light can be seen through a tarp, the tarp should not be used. Caution should be exercised during the deployment of tarps on damaged equipment because a wet tarp may become energized and conduct hazardous current if it contacts live parts. Firefighting foam should not be relied upon to block light from reaching the PV panel.

• Even at night, when illuminated by artificial light sources such as fire department light trucks or an exposure fire, PV systems are capable of producing electrical power sufficient to cause a lock-on hazard – that is, the inability to control muscles and let go of the electrically energized part.

• Severely damaged PV arrays are capable of producing hazardous conditions including electrocution. Damage to the array may result in the creation of new and unexpected circuit paths. These paths may include both array components (module frame, mounting racks, conduits, etc.) and building components (metal roofs, flashings and gutters). Care must be exercised during all operations, both interior and exterior. Contacting a local professional PV installation company should be considered to mitigate potential hazards.

• Damage to modules from tools may result in both electrical and fire hazards. The hazards may occur at the point of damage or at other locations, depending on the electrical path. Metal roofs present unique challenges in that the surface is conductive, unlike other roof types such as shingle, ballasted or single-ply designs. Firefighters’ gloves and boots afford limited protection against electrical shock, provided the insulating surface is intact and dry. They should not be considered equivalent to electrical personal protective equipment.

• Responding personnel must avoid or exercise extreme caution near the roofline because modules or sections of an array could slide off the roof.

• Fires under an array but above the roof may breach roofing materials and decking, allowing fire to propagate into the attic space.

Ongoing research through development of experiments is helping assess the new risks in fighting fires involving PV panels and providing the foundation to modify current and develop new firefighting practices to help reduce firefighter death and injury.

The results of these experiments provide a technical basis for the fire service to examine its equipment, tactics, standard operating procedures and training content. Several tactical considerations were developed using the data from the experiments to provide specific examples of potential electric shock hazards from PV installations during and after a fire event.

All innovation is met with emerging benefits and risks. Mitigating the risks is important to allow for further innovation and to increase adoption knowledgably and responsibly. This is the case with the growing use of PV systems, which continue to evolve to be more efficient and more reliable.