Issue 92: Fire Concerns with Roof-Mounted Solar PanelsBy Richard J. Davis, P.E., FSFPEAs companies look to reduce their dependence on fossil fuels, manyare turning toward rooftop photovoltaic (PV) power systems, or solarpanels, as a source of renewable, clean energy. However, this technologycomes with specific risks. One of the many dangers to solar panels ishow the panel and its mounting system impact the combustibility of theoverall roof system. Some solar panels, for example, include a backingof highly combustible plastic.In laboratory-based fire tests of roof assemblies, 1, 2 the maximum allowable fire spread is between approximately 20 and 40 ft 2 (1.9 and 3.7 m 2),depending on whether an A, B or C rating is desired. In actual rooffires with roof-mounted solar panels, fire damage has involved areas ofbetween 1,000 and 183,000 ft 2 (93 and 17,000 m 2).
Solar panels present firefighters with new challenges A department is creating a curriculum on handling solar panels in a fire, including how to cut through the roof and how to disconnect the.
In the most extreme case the fire spread to the inside and destroyed the entire building (see Fig. PV roof fire at a refrigerated warehouse in NJ in 2013(photo courtesy of Vince Lattanzio, NBC Philadelphia)While the results of a lab test and an actual fire are not alwaysidentical, such a wide disparity is reason for concern. Lab testsconducted by at the FM Global Research Campus in West Glocester, RI,USA, confirm these concerns.
For such testing, an ASTM E108 testapparatus was utilized, placing PV panels over a commonly used, ClassA-rated roof assembly (when the roof alone was tested), starting nearthe flame-exposed end. This roof assembly failed the test (see Fig. 2).While only one failure mode is required by the test standard, in thistest all three of the following failure modes occurred: Fire spreadlaterally to both edges of the sample, material continued to burn afterfalling to the floor, and fire spread across the 13 ft (4 m) length ofthe assembly within 90 seconds.Fig. Fire test of rigid PV panels over Class A-rated roofconsisting of anEPDM cover over polyisocyanurate insulation (photocourtesy of FM Global)Why did this happen? Regardless of the materials used in theconstruction of a PV panel, its mere presence changes the dynamics of afire involving a roof assembly.
Research tests done at UnderwritersLaboratories 3, 4, 5, 6,7,8, 9, 10, 11 demonstrate that even acement panel simulating the presence of a PV panel will increase firespread across a common roof assembly.There are three key considerations that affect fire spread along a roof where a roof-mounted PV array is installed:.In a typical roof fire, the flame is primarily vertical, or perhapssomewhat slanted due to wind. Once such flames spread under a PV panel,the flame is redirected much closer to the roof surface and nearlyparallel to it. This increases the incident heat flux on the roofsurface, often above its critical heat flux.While the exterior fire classification of a roof is an effective wayto rate the exterior fire performance of roof assemblies, even a Class Aassembly will offer some fuel contribution to a roof PV fire, with moststanding seam metal roof systems being the exception.While the top surface of a rigid PV panel is usually made of temperedglass, the bottom of the panel may contain combustibles (used to protectthe PV circuitry) in the form of polyester-based encapsulants and backsheets (see Fig.
If this ignites and the heat re-radiates, firespread is likely to continue back and forth beneath the roof assemblyand the PV back sheet.Fig. The underside of a rigid PV panel(photo courtesy of FM Global)PV rooftop fires have been caused by electrical arcs that occurs nearthe combiner box, where numerous wires from PV panels are connected.This is a location where there is considerable voltage, before thecurrent is converted from DC to AC at the inverter, and where the roofassembly could ignite and result in fire spread under the PV panels.Fortunately, there have been some improvements made by manufacturersduring the past few years with regard to the electrical components thatcan reduce the potential for ignition. Some PV panels havemicro-inverters on each PV panel, which convert voltage from DC to AC.This can be expensive, but it reduces the probability of ignition.Manual firefighting efforts also can be hampered by the electricalrisk associated with PV arrays. While minimum 4 ft (1.2 m) wide aislespaces between panels at a maximum of 150 ft (46 m) apart have beenrecommended 12, this does not alleviate all the risk.Disconnecting electrical power from the PV array is complicated, andarrays continue to generate electricity, sometimes even at night. The PVarray and the roof assembly should be designed so their constructionlimits potential fire spread and the entire burden for fire protectionis not placed on manual firefighting efforts.There are several design choices that can limit fire spread if ignition occurs:.Use a complete system (PV panels, securement, and roof assembly) thathas been tested to simulate actual field conditions. FM Approval isavailable, 13 which includes testing for fire exposure as well as wind and hail.If the existing roof has aged, it is recommended that a new roof beinstalled before installing a PV system.
Choose roof assemblies thatlimit potential fuel contribution in the event of an exterior fire.Appropriate options include metal roof systems, as well asnoncombustible materials (such as gypsum cover boards, mineral wool orexpanded glass roof insulation) installed directly below single-ply ormulti-ply roof covers. In some cases, coatings may need to be applied tothe top of the roof cover.Where existing roofs will remain, investigate the need for a coatingto be applied to the top of the roof cover that will improve performancewith regard to exterior fire exposure.
Construction materials that meltat low softening temperatures and can flow when burning (such asexpanded or extruded polystyrene insulation or multi-ply roof covers)may require protection such as a gypsum cover board installed over theinsulation or a coating over the roof cover.To prevent an exterior fire from entering the building, protectbuilding expansion joints by securing mineral wool or otherfire-resistant compressible insulation between wood nailers, covered bysteel flashing.Evaluate the potential for fuel contribution from the underside of thePV panel. The underside of the panel may have a glass backing, aluminumor fluoro-polymer-based back-sheet as an alternative to apolyester-based back-sheet.Most importantly, it is best to use a PV panel that has passed a fire test with the proposed roof assembly.For additional information, see.Richard Davis is with FM Global.ASTM E108, Standard Test Methods for Fire Tests of Roof Coverings, ASTM International, West Conshohocken, PA, 2011.UL 790, Standard for Standard Test Methods for Fire Tests of Roof Coverings, Underwriters' Laboratories, Northbrook, IL, 2004.Backstrom, B.
& Tabaddor, M. 'Effect of Rack Mounted PhotovoltaicModules on the Fire Classification Rating of Roofing Assemblies,'Underwriters' Laboratories, Northbrook, IL, 2010.Backstrom, B. & Tabaddor, M. 'Effect of Rack Mounted PhotovoltaicModules on the Flammability of Roofing Assemblies – Demonstration ofMitigation Concepts,' Underwriters' Laboratories, Northbrook, IL, 2010.Backstrom, B.
'Effect of Rack Mounted PhotovoltaicModules on the Fire Classification Rating of Roofing Assemblies - Phase2,' Underwriters' Laboratories, Northbrook, IL, 2012.Backstrom, B. 'Characterization of PhotovoltaicMaterials – Critical Flux for Ignition/Propagation - Phase 3,'Underwriters' Laboratories, Northbrook, IL, 2012.Backstrom, B. 'Report of Experiments of Minimum Gapand Flashing for Rack Mounted Photovoltaic Modules - Phase 4,'Underwriters' Laboratories, Northbrook, IL, 2012.Backstrom, B. 'Considerations of Module Position onRoof Deck During Spread of Flame Tests - Phase 5,' Underwriters'Laboratories, Northbrook, IL, 2012.Backstrom, B. 'Validation of 42” PV Module Setback onLow Slope Roof Experiments - Project 7,' Underwriters' Laboratories,Northbrook, IL, 2012.Backstrom, B. ' Validation of Roof Configuration 2 Experiments - Project 9,' Underwriters' Laboratories, Northbrook, IL, 2012.Backstrom, B.
& Fischer, C.' Report on Spread of Flame and BurningBrand Performance of Generic Installations,' Underwriters'Laboratories, Northbrook, IL, 2012.' Solar Photovoltaic System,' Los Angeles City Fire Department Requirement No. 96,Los Angeles, CA, February, 2009.Class Number 4478, ' Approval Standard for Rigid Photovoltaic Modules,' FM Approvals, Norwood, MA, 2012.Related Articles:3rd Quarter 2014 – Harnessing the Sun: Solar Power and Fire Protection Engineering – Casey C. Grant, P.E., FSPEDevelopments in the solar power field are proliferating at an everincreasing rate, raising new questions about safety and reliability.These developments are necessitating the re-examination and modificationof codes and standards and other instruments of the existing safetyinfrastructure.
The expertise of fire protection engineers is importantfor the advancement of solar power technology in order to preventunwanted events before they occur, or to mitigate any adverse eventsonce they do occur.3rd Quarter 2012 – Facing the Future: Alternative Energy and Fire Protection Engineering – Casey C. Grant, P.E., FSPEThe increased demand for alternative energy sources and technologies isintroducing new challenges for fire protection professionals, includingthe re-evaluation of existing codes and standards. Casey Grant exploresthe impact that alternative energy sources – both traditional and newerforms, such as fuel cells, Smart Grid, and concentrated solar power –will have on fire protection design as engineers work to mitigate anypotential hazards that incorporating these new forms of energy mightpresent.For questions concerning delivery of this eNewsletter, please contact our Customer Service Department at (216) 931-9934.
A year ago, fire trucks arrived on the scene of a blaze at a cheese and deli-meat distribution facility just outside of Philadelphia. But firefighters had to keep their distance because of worries that the thousands of solar panels on the roof were still generating power, putting them at risk of electrocution. The building was completely destroyed.To make sure that the same thing doesn't happen in Ontario, where the majority of Canada's solar installations are located, firefighters and the solar industry association have created new guidelines to ensure those arriving at the scene of a fire are aware of the presence of panels, and know how to deal with them.On Tuesday, the Ontario Association of Fire Chiefs and the Canadian Solar Industries Association will launch a training manual for fighting fires in these circumstances. They will also ensure that industrial buildings with solar panels on their roofs be marked so that arriving firefighters know they are there. All fire halls will get the manuals by early in 2015. The key issue, said Meaford, Ont., Fire Chief Mike Molloy, is that solar panels keep generating power even if they are disconnected from an electrical system or grid. Even at night, the lights from a fire truck are enough to produce some power out of the panels.In some circumstances involving fires at buildings with solar panels, foam might be used instead of water to fight the fire, or water may be spayed in a broad stream instead of in a direct stream – so electricity can't travel up the water to reach the firefighter.
The weight of the panels can also mean a roof might collapse sooner than it would have otherwise, if it becomes compromised during a fire, Chief Molloy said.' Solar panels don't cause fires, but they can be present on buildings that have fires,' said John Gorman, president of the Canadian Solar Industries Association. Situations such as the fire outside of Philadelphia underline how crucial it is that first responders be protected, he said.It is also important that these kinds of safety issues don't become a roadblock to future solar installations. 'We want solar to continue to be well supported by the Canadian public,' he said.Mr. Gorman said the training program will eventually be rolled out in other provinces as solar power takes hold outside of Ontario.The guidelines for firefighters would also apply to fires on houses, as well as on industrial buildings.
Chief Molloy, who served on the committee that developed the new guidelines, said the rapid expansion of solar power means this issue will be more and more important. In the small town of Meaford alone, he said, there are four solar panel systems in place and 'there are proposals going on monthly to add more and more photovoltaic sources on top of the shopping centre, or on top of the hardware store.' He said one reason buildings with solar panels need to be marked is that some panels are built into the exterior glass and are not at all obvious. Firefighters need to know about these 'building-integrated' panel systems, he said.