The following is an updated review of the fire hazards of Solar Photovoltaic (PV) Panels. Previous Risk Logic articles from January 2015 and January 2014 still apply but new data has entered the field of property loss prevention with regard to this challenging hazard.
The publication of FM Global’s Data Sheet 1-15, Roof Mounted Solar Photovoltaic Panels was last updated October 2014. Since then additional upgrades have been provided to reduce the fire loss exposure.
Below is a 2013 fire loss that occurred in New Jersey with regard to a roof fire started by an arc of a PV panel array. More than 7,000 solar panels on the roof of a burning Dietz & Watson warehouse in Burlington County proved too much of a hazard for firefighters.
“We may very well not be able to save buildings that have alternative energy,” William Kramer, New Jersey’s acting fire Marshall, said after Delanco Fire Chief Ron Holt refused to send his firefighters onto the roof of the 300,000-square foot Dietz & Watson facility. Solar panels are particularly hazardous to firefighters for a number of reasons, according to Ken Willette, a division manager with the National Fire Protection Association (NFPA).
“There is a possibility of electric shock because the electricity to the panels can’t be shut off,” he said, “and not having a clear path on the roof to cut a ventilation hole is another challenge.”
Essentially, solar panels, comprised of photoelectric cells, generate electricity from solar radiation, and any kind of light at all, said Willette, will activate the panels, including “streetlights, floodlights, even firefighters’ flashlights. Those panels are extremely efficient.” Those fighting the Dietz & Watson blaze were hampered by water supply issues, too, according to Kramer, and even as much of the fire had died out by today, the building was still being doused with water from fire hoses.
Electric shock and slipping and tripping on solar panel roof displays are just two of a number of potential hazards in fighting fires at “green” structures, say experts. Others include structural collapse because of the weight of the panels on the roof and inhalation exposure as solar batteries exposed to fire are capable of generating extremely caustic fumes and gases.
The installation of thousands of solar panels on the roof of the warehouse in Delanco Township hampered firefighting efforts from Sunday afternoon until Monday evening, officials said. A Star-Ledger file photo of solar panels.
Although the maximum voltage of a solar panel system is just 600 volts, a low voltage, according to the Division of Fire Safety, from “even a momentary contact … can produce continuous shock, thermal injury and ventricular fibrillation.”
In a recent report, the Fire Protection Research Foundation said, “The inability to de-energize individual photovoltaic panels exposed to sunlight cannot be overemphasized. It is absolutely imperative that emergency responders always treat the systems and all its components as energized. This includes after the emergency event is stabilized, as the system will continue to be energized while exposed to sunlight, possibly with damaged system components that could present serious shock hazards or even cause a rekindling of a fire.”
Even without the solar panels, said Willette, “A 300,000-square-foot building poses a substantial firefighting challenge. A building like that will burn a long time.”
There are several hazards to consider such as wind, building collapse, hail & fire; however the fire peril appears to be the most hazardous for roof mounted PV panels.
Up until 2014 adherence to the current National Electric Code (NEC) may not provide adequate protection against a fire initiating from a ground fault condition for a PV panel array. There are specific recommendations for current monitoring/sensing equipment to address DC ground fault situations, as well as several other items for electrical safeguards. It is important to know if the PV system was installed per the 2014 NEC, specifically Article 690. If so, the installation will include Ground Fault Protection. Article 690.5 (A – C) spells out what is required:
The ground-fault protection device or system shall:
- Be capable of detecting a ground-fault in the PV array “DC current carrying conductors” and components including any intentionally grounded conductors
- Interrupt the flow of fault current
- Provide an indication of the fault
- Be listed for providing PV ground fault protection
NEC Article 690.11 (Arc-Fault Circuit Protection) states that DC PV systems with DC source circuits, DC output circuits or both operating at a PV system maximum voltage of 80 Volts or greater, shall be protected by a listed DC arc-fault circuit interrupter, PV type or other system components listed to provide equivalent protection. The PV arc fault protection means shall comply with the following requirements:
- The system shall detect and interrupt arcing faults resulting from a failure in the intended continuity of a conductor, connection, module, or other system component in a DC PV source and output circuits
- The system shall require that one disabled or disconnected equipment be manually restarted
- The system shall have an annunciator that provides visual inspection that the circuit interrupter has operated; this indication shall not reset automatically
Also updated in the 2014 version of the NEC is Article 690.12, which calls for a rapid shutdown function that controls specific conductors of the PV systems.
It is important to know which PV systems were installed per the 2014 NEC Code. For older systems not meeting the 2014 NEC Code, Residual Current Detection / Differential Current Monitoring (DCM) should be installed. The DCM technology allows you to know if there is current flowing on the PV system’s ground leg, thus indicating a short condition that should not be present under normal operating conditions. Latent short conditions that remain undetected can lead to faults and intense fires.
Another important part of the fire risk is the access to the roof. NFPA 1, Fire Code, spells out what is needed for access pathways:
- 4 ft. aisles every 150 ft. are required
- Should be over structural members
- Centerline axis pathways should be provided in both axes of the roof
- Centerline axis pathways should run on structural members or over the next closest structural member nearest to the centerlines of the roof
- Should be straight line not less than 4 feet clear to skylights and/or ventilation hatches
- Should be straight line not less than 4 feet clear to roof standpipes
- Should provide not less than 4 feet clear around roof access hatch with at least one not less than 4 feet clear pathway to parapet or roof edge
- PV Arrays should be no larger than 150 ft. x 150 ft.
Also preventive maintenance is critical. Infrared scans should be conducted at least annually on conduit to check for hotspots.
When considering a PV roof installation, your first point of contact should be the local fire department. You should find out how they would fight a fire in your facility. Do they have the apparatus to fight a roof top fire? Has the FD been on site for a preplanning meeting with regard to fighting a PV roof fire?
Usually the panels are owned by a 3rd party. What operations and maintenance plan is provided and who is responsible for the maintenance: the PV panel provider or the building owner? These are critical points of interest as well.
When considering installing PV panels on a roof. Consider the life and type of the roof and the life of the PV installation. Never install a PV panel array on a roof that is nearing the end of its life span. It’s best to install a PV array on a new roof system that is FM approved. FM disallows the use of any PV panel systems using foam plastics, unless specifically FM approved as part of the assembly. FM Approval Standards 4476 and 4478 for Flexible and Rigid PV Modules address fire, simulated wind uplift, hail damage, and heat aging of the panels as part of the finished roof assembly.
Risk Logic, Inc. can answer your questions regarding the PV panel property loss prevention exposure and advise you as to how it can apply to your facility.
Reference Articles:
FM Global DS 1-15 Roof Mounted Solar Photovoltaic Panels
NFPA 1 Fire Code & NFPA 70 National Electric Code
“Update to the 2014 NEC” by Ward Bower Innovations LLC
NJ.Com on Dietz & Watson Fire Loss