Fires in Photovoltaic Systems: Lessons Learned from Fire Investigations in Italy

Issue 99: Fires in Photovoltaic Systems: Lessons Learned from Fire Investigations in Italy

By Luca Fiorentini, Luca Marmo, Enrico Danzi and Vincenzo Puccia

Over the past decade the number of new photovoltaic (PV) system installations has increased sharply throughout the world. With this growth, the associated risks grew significantly. This included an increase in the number of fire incidents involving PV systems. For example, it is estimated that in Italy alone over 700 fires involving PV systems occurred in 2012. This has drawn the attention of the fire safety community and facility managers.

This article will assess some of the fire risks associated with of PV system installations based on fire investigations conducted in Italy.

Fire Problem

The growth of photovoltaic system roof installations has been a result of public incentives for green energy. Some of the fire incidents associated with PV systems involved large roof fires and were often followed by an interior compartment fire. Some of these fires even resulted in the loss of the structure. The investigations into these fires revealed that DC arcing and the ignition of combustible roof insulation, often polyurethane or polystyrene foam, were often contributing factors in these fires.

The losses that have resulted from these events could have been reduced by implementing a risk analysis approach in the early design stages of these installations. This should include evaluating the fire risk of the most common failures associated with a PV installation, such as cell mismatch, DC arcing, and localized fires in connection boxes or PV modules.

At the same time, in Italy there was a short time period for building owners to access the public incentives. This resulted in compression in the timing for engineering, procurement, and construction of these projects, which resulted in the lack of standardization for the specific PV materials. This along with the inexperience of installers led to an undervaluation of the fire risk associated the PV system and the building housing the installation.

Figure 1: A photovoltaic system fire.

The available data on PV plant fires in Italy includes fire incidents ranging from fires in an electrical connection, to a limited fire of few PV modules, to a large fire on the roof of the building spreading inside through the skylights.

Table 1: Fires related to Photovoltaic Installations, courtesy of Italian National Fire Corp, Statistical Service.

Table 1 refers to the number of incidents related to fires of various magnitudes that involved, but not necessary started from, PV system installations in Italy. The analysis of the data shows the number of fires peaked in 2012 following the first wave of installations. Since these fires involved new installations, the lack of qualifications of designers/installers played a role in these fires. This included the incorrect management of shading, the exposure of plant components to substandard conditions (heavy water condensation under the panels), low quality components, crushing of cables during the installation, under-evaluation of typical DC current behavior, and mismatch of PV cells.

Figure 2: A fire in a connection box in a ground PV system.

Figure 3: DC arcing effects on an external side of polyurethane.

Additionally as shown in Table 1, after 2012 the number of fires involving PV system installations has dropped as the market for PV-related services decreased. This has led to a better qualified workforce to install these systems. At the same time, better product standards and an increase in national regulations have also helped. Moreover, after the first relevant fires occurred, most PV panels producers started to include fire resistance requirements in the installation procedures.

Figure 4: A 1000 sq. meter warehouse housing a roof-mounted PV system.

Fig. 5A

Fig. 5B

Fig. 5C

Figures 5A, 5B and 5C – A fire involving a PV system produced citizen concerns in regards to pollution and public safety.

Figure 6 -- A large warehouse fire strongly influenced in its growth by the PV system.

Fire Hazards

Based on this assessment, the following common fire scenarios were observed:

• A building compartment fire spreading through openings and propagating to the roof
• Fire starting in PV modules installed on a roof with fire spreading to the building compartment.

Additionally, PV plant components on a roof or on a building façade could:

• Alter the spread of fire outside or throughout the building.
• Result in combustion products interfering with the smoke and venting systems.
• Be an obstacle to firefighting operations.
• Introduce a safety hazard to firefighters as a result of the presence of energized electrical components.

Moving Forward

A preventive fire risk assessment on the PV roof configuration could easily identify the inherent dangers associated with coupling a strong fire load with an almost unavoidable ignition source. Also, skylights or the smoke evacuation systems can be a pathway for internal fire spread.

Based on the results of investigations of fires that occurred in PV system installation in Italy, there is a need for a comprehensive review of the fire and building code requirements for PV roof installations. Specifically, these requirements should address combustible insulating and roof materials located below active PV system components.

Luca Fiorentini is with Tecsa Srl, Luca Marmo is with Politecnico di Torino, Enrico Danzi is with Politecnico di Torino, and Vincenzo Puccia is with National Fire Corps.

Bibliography

[1]   Ignition Handbook, V.Babrauskas
[2]    SFPE Handbook of Fire Protection Engineering 3rd Ed.,  SFPE Quincy, Mass.(U.S.)
[3]    Numerical simulation of fire spread on polyurethane foam slabs K. Prasad, N. Marsh, M. Nyden, T. Ohlemille ,M. Zammarano, Fire Research Division BFRL, NIST Annual Fire Conference, 2009
[4]    Performance of polyurethane (Pur) Building products in fires, W. Wittbecker D. Daems U. Werther, ISOPA
[5]    Fire Properties of Polymer Composite Materials, A.P. Mouritz A.G. Gibson, Springer Verlag
[6]    Guide Blu, Fotovoltaico, V.Carrescia
[7]    Fire Performance Of Polyurethane Steel Deckroofing, I.Kotthoffr,R. Walterf, W.Wittbecker, ISOPA
[8]    Technical Briefing: Fire Performance Of Sandwich Panel Systems Association of British Insurers (Partially Revised August 2008) May 2003
[9]    Solar America Board for Codes and Standards (Solar ABCs) Report, www.solarabcs.org/interimflammability
[10]  Solar America Board for Codes and Standards (Solar ABCs) Impacts on Photovoltaic Installations of Changes to the 2012 International Codes www.iccsafe.org

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