UL researchers have led the discovery around fire risks associated with PV panels, developing a standard for arc fault protection for PV systems and being among the first to specifically address fire service operational hazards.
The use of photovoltaic (PV) systems as an energy-generation source is growing at a rate of 30 percent annually due to governmental incentives and rising traditional energy costs. As a result of greater utilization, traditional firefighter tactics for suppression, ventilation and overhaul have been complicated, leaving firefighters vulnerable to potentially unrecognized exposures (particularly due to risk of electrocution). Though the electrical and fire hazards associated with electrical generation and distribution systems are well-known, PV systems present unique safety considerations.1
WHAT DID UL DO?
UL is empowering firefighters with knowledge during critical decision-making moments regarding how to react when encountering new situations and potential hazards caused by PV panel technologies.
In the past several years PV systems have advanced, producing more energy and becoming more accessible to the average homeowner. Just eight years ago, PV panels converted only 6 percent of the solar energy they absorbed into reusable energy. Today they convert 25 percent of the energy. Importantly, the increase in absorption and conversion has resulted in panels that are much more efficient but also much hotter than before. The increased operating temperatures mean that PV panels can no longer be placed flush against a roof, but are now 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. UL researchers have led the discovery around fire risks associated with PV panels, developing a standard for arc fault protection for PV systems and being among the first to specifically address fire service operational hazards.2
In 2011 our scientists constructed a functioning PV array to serve as a test fixture under the U.S. 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 W each (5,980 W total rated power). 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.3
The study addressed shock hazard due to the presence of water and PV power during suppression activities; shock hazard due to the direct contact with energized components during firefighting operations, emergency disconnect and disruption techniques; shock hazard due to severing of conductors; assessment of PV power during low ambient light, artificial light and light from a fire; and assessment of potential shock hazard from damaged PV modules and systems.
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.4
- 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 power from the PV to near zero. UL has found that 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 equipment. Firefighting foam should not be relied on to block light.5
- 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.6
- 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.7
- 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.8
- 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.9
- Responding personnel must stay away from the roofline because modules or sections of an array could slide off the roof.10
- Fires under an array but above the roof may breach roofing materials and decking, allowing fire to propagate into the attic space.11
Research is also being conducted to examine the impact of PV panels — from present concerns, such as simulating the effects of wildfires getting into the PV panels to potential future effects by developing ways to simulate 30 years of aging in one year.
WHY IT MATTERS
These studies developed the empirical data needed to quantify the hazards associated with PV installations. This data provides the foundation to modify current or develop new firefighting practices to 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 utilizing the data from the experiments to provide specific examples of potential electrical shock hazards from PV installations during and after a fire event.