Fire Safety of Building Integrated Photovoltaic Systems: Regulatory Gaps for Solar Façades
By: Yoon Ko, PhD, Monireh Aram, Xin Zhang, and Dahai Qi, PhD
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With the advancement in Photovoltaic (PV) technologies, PV modules are often integrated into building skins, glass walls and skylights creating solar exterior claddings and solar roofs. These building integrated photovoltaic (BIPV) systems while serving as a building element, generate electricity on-site. Thus, BIPV systems need to meet fire safety requirements both as energy generating systems and as building components. However, the current BIPV standards are quite limited in addressing the fire safety performance requirements of BIPV as building components/structures. A systematic review was conducted 1 on regulations and standards pertaining the fire safety of BIPV systems, and this article summarizes the regulatory gaps of BIPV façades that were presented at the 14th SFPE International Conference on Performance-Based Codes and Fire Safety Design Methods.
Fire risks of BIPV façades and an overview of regulatory framework
The fire risks of BIPV systems are of particular concerns since fire involving BIPV glazing and façade would become a direct life safety threat to building occupants.2 PV modules are made of multiple layers, including combustible materials (e.g., top layers made of Polyethylene Terephthalate (PET), polymethyl-methacrylate etc., and encapsulants made of ethylene-vinyl acetate copolymer).3 In addition, recent small-scale fire tests 4 reported the detection of toxic gases of sulfur dioxide, hydrogen fluoride, hydrogen cyanide and VOCs from PET laminated PV fires. BIPV products are more vulnerable than other regular building materials since they can self-ignite from physical, environmental, and electrical causes, as shown in Figure 1. Also, potential fire hazards typically exist in heated PV modules even in normal operation with the operation temperature reaching as high as 100°C. 5
Overall, every BIPV exterior façade/wall claddings is currently required to comply with the following fire safety requirements:
- Electrical requirements for BIPV module/system
- Reaction-to-fire requirement as building materials
- Fire-resistance requirement as building component/system
The electrical requirements are addressed in PV specific standards (e.g., IEC/UL 61730,6 UL 1703,7, IEC 612158 and UL 67039). For the requirement as building materials/components, most global standards (e.g., EN 50583,10 IEC 6309211 and ANSI/UL 17037) refer to the current local building codes and construction regulations although they do not provide BIPV specific fire safety requirements.
Figure 1 Classification of PV fire incidents based on the faults 2
BIPV material requirement for reaction-to-fire
As construction materials, PV products are required to be evaluated for their fire behaviour at material level, such as combustibility, ignitability, heat and smoke generation, and flame spread. However, PV specific test methods or enhanced performance requirements are not yet suggested by the current codes/standards. It is not yet verified if the current test methods and requirements are sufficient to evaluate actual burning behaviours of PV products while electrically active. For example, the flame spread ratings obtained by the current codes/standards (e.g., ULC S102, ASTM E84) might fail to characterize the actual flame spread behaviour over the BIPV claddings when they are electrically active and normally heated during the operation.
Resistance to fire originating from BIPV façade
As reported for combustible claddings involved in recent catastrophic high-rise building façade fires, smoke and flame tend to propagate rapidly via the cavity space behind the regular claddings as well as BIPV claddings. More importantly, BIPV cladding systems could pose higher fire risks than other regular claddings since they can self-ignite. In designing ventilated BIPV cladding systems (i.e., with the cavity space created due to the mounting mechanism between the primary exterior wall and the external facing panels, see Figure 2-(a)), it should consider the fire risks associated with the heat from the PV system operation released via the cavity unless there is no other cooling mechanism designed for the solar systems , as well as the PV fire induced smoke spread and control.12
Requiring protective barriers could be solutions to resist the spread of fire originating from the PV exterior claddings. Currently, the IBC (The International Building Code) in the US requires thermal barriers when a cladding system contains a certain insulation layer, to separate the cladding from the interior of the building.
Resistance of BIPV façade to fire exposure from within a building
Solar claddings/curtain walls shall be designed based on evaluations for fire resistance requirements by the local building codes, as per e.g., EN 50583 10. Claddings including BIPV claddings could be mounted to primary exterior walls, and the claddings should not affect the fire resistance rating of the primary exterior walls.
When PV curtain walls alone are installed where a fire rating is needed, the entire assembly needs to be tested by the standard fire resistance tests (see Figure 2-(b)), like other curtain walls, by exposing to the standard fire curve (e.g., ASTM E119). The failure criteria include threshold temperature increases on the un-exposed side. It is questionable whether the current temperature criteria are applicable to the PV curtain walls since the PV face could be heated up to about 100°C in even normal operation.
Resistance to fire spread on BIPV façade
For the vertical fire spread testing, the current local building codes require combustible claddings and curtain walls pass large-scale façade fire spread tests, such as NFPA 285 and CAN/ULC S134 tests (see Figure 2-(c)).
However, it is not yet evaluated if these test methods are sufficient, and the pass-fail criteria are appropriate to address unique fire risks posed by BIPV facade. It should be noted that rapid fire spread over the exterior façade systems is attributed to the PV normal operation temperature; combustibility of PV and substrate layers; and designs of mounting systems.
Fire safety requirements for BIPV double skin façade
The BIPV Double Skin Façade (DSF) is a novel façade technology used in new buildings as well as retrofit projects. The PV DSF consists of two skins, and PV systems often form the exterior skin added to the primary exterior wall/skin, as shown in Figure 3-(a). Both skins could be glazing, and the distance between the two could be up to 2 meters. In general, the fire safety requirements are more stringent to accessible DSF than non-accessible DSF. Non-accessible DSF systems, with the plenum space free of horizontal slabs or fire stop, need to meet the local code requirements.
Concerning the fact that fires could start from the PV skin, the BIPV DSF should be designed for smoke and fire protection since smoke and flame could propagate through the plenum space endangering the occupants inside the building. Computational Fluid Dynamics simulations conducted by 14 reported significant smoke spread from BIPV DSF to the building inside, as shown in Figure 3-(b). Detailed design requirements for the PV DSF are not yet available, and the fire risks of the PV DSF is required to be further investigated.
Regulatory gaps for solar façade
Through the review of the standards and codes summarized above, following gaps are concluded for the solar façade:
- The current BIPV standards are quite limited in addressing the fire safety of BIPV facades as building elements/system, as the fire safety requirements/testing methods are relayed back to the local building codes/standards, which are developed for ordinary construction systems.
- The current fire safety test and performance requirements should be re-evaluated in adopting BIPV façade systems, to address the unique challenges and reflect the actual burning behaviour of PV modules when electrically active in operation.
- New standards and test methods are necessary to address the fire spread and toxic smoke infiltration hazards specific to BIPV façade, including cladding, curtain wall, DSF and glazing systems.
- Regulatory reviews are also necessary to evaluate any additional fire protection system requirements for PV fires in terms of effective fire detection, fire suppression and safe occupant evacuation as well as firefighting.
Yoon Ko, PhD is with Fire Safety Research Unit, National Research Council Canada, and the Department of Civil and Building Engineering, Université de Sherbrooke, Canada
Monireh Aramb, Xin Zhangb, and Dahai Qi, PhD, are with Department of Civil and Building Engineering, Université de Sherbrooke, Canada
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