Underwriters Laboratories (UL) released the results of a study intended to examine the hazards presented by photovoltaic (PV) systems, which use one or more solar panels to convert sunlight into electricity, and the potential impact on firefighting operations. These concerns included firefighter vulnerability to electrical and casualty hazards when mitigating a fire involving PV systems.
Solar panels aren’t just found on the West Coast anymore; they are increasingly becoming popular as an alternative, economical means of powering houses and other structures. The UL report noted that the use of PV systems is growing at a rate of 30% annually. Yet until this study, not much was known about the way traditional firefighter tactics for suppression, ventilation and overhaul affect PV systems.
As UL noted, “This fire research project developed the empirical data that is needed to quantify the potential hazards associated with fire scenarios involving PV installations and provides the basis for the development of firefighting operational practices to reduce firefighter death and injury.”
The Test
UL constructed a functional PV array experimental fixture at its Northbrook, Ill., campus. This fixture provided for experiments to:
- Develop knowledge of the hazard of the application of water to PV installation during suppression tactics.
- Generate understanding of effective de-energizing practices such as deployment of salvage tarps and limitations of disconnect devices.
- Address concerns about power generation during low and artificial light conditions.
In addition, experiments were conducted on functioning PV arrays at Delaware County Emergency Service Training Center. A series of experiments were conducted on three PV technologies–metal framed glass on polymer, flexible laminate, and building integrated roof shingles. Fire experiments were designed to represent a room of content compartment fire which evolved to a structure fire, ending in collapse. Experiments were also conducted on a rack-mounted PV arrays to represent a debris fire under the PV modules above the roof.
Following the fire experiments, the PV modules were examined to determine their ability to generate power representing potential safety hazards for firefighters, particularly during overhaul operations.
The Recommendations
UL issued the following recommendations as a result of the study:
- The electric shock hazard due to application of water is dependent on voltage, water conductivity, distance and spray pattern. A slight adjustment from a solid stream toward a fog pattern (a 10 degree cone angle) reduced measured current below perception level. Salt water should not be used on live electrical equipment. A distance of 20 feet had been determined to reduce potential shock hazard from a 1000 Vdc source to a level below 2 mA considered as safe. It should be noted that pooled water or foam may become energized due to damage in the PV sytem. A summary of the distances and spray patterns which measured safe (< 2 mA) and perception (< 40 mA) currents for various PV system voltages is shown in Appendix A.
- Outdoor weather exposure rated electrical enclosures are not resistant to water penetration by fire hose streams. A typical enclosure will collect water and present an electrical hazard.
- Firefighter’s 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 PPE.
- Turning off an array is not as simple as opening a disconnect switch. Depending on the individual system, there may be multiple circuits wired together to a common point such as a combiner box. All circuits supplying power to this point must be interrupted 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, on a PV array, there is no single point of disconnect.
- 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 PV to near zero. As a general guide, if light can be seen through a tarp, it should not be used. Caution should be exercised during the deployment of tarps on damaged equipment as a wet tarp may become energized and conduct hazardous current if it contacts live equipment. Also, firefighting foam should not be relied upon to block light.
- 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.
- Severely damaged PV arrays are capable of producing hazardous conditions ranging from perception to 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 hazard 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 types such as shingle, ballasted or single ply.
- Severing of conductors in both metal and plastic conduit results in electrical and fire hazards. Care must be exercised during ventilation and overhaul.
- Responding personnel must stay away from the roofline in the event of modules or sections of an array sliding 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.
More Resources
Access the full report and the executive summary of this study. In addition, UL has developed a user-friendly online training program featuring a professionally narrated description of all of the experiments, their results and the tactical considerations. Experimental video is used and graphical data is explained in a way that brings science to the street level firefighter.
