Solar panels are being installed on more and more industrial flat roofs. Fortunately, these buildings rarely catch fire, but what are the real facts behind the fires that have occurred and what can we learn from them?
At the request of Stybenex, Efectis Nederland has conducted research into fires on industrial flat roofs with solar panels. Very few fires occur on industrial roofs with solar panels. Efectis was able to identify and assess eight fires in the period 2016-2021, using information provided by the fire departments involved, and images available on the internet. Efectis examined the cause, development, properties and characteristics of each fire and, more specifically, the role of insulation materials. This enabled the researchers to describe measures that promote the safety of flat roofs with solar panels.
Research and testing
What is already known about fire spread on flat roofs with solar panels?
Up to now, research in this area has focused mainly on the origin of fire in a solar panel or in the installation components. However, the aim of Efectis was to investigate fire development under solar panels. Three studies under laboratory conditions are available and offer some insight.
Higher rate of fire spread
The distance between solar panels and the roof appears to have a major influence on the temperature and the rate of flame spread. Some researchers have noted that the fire development partly depends on the burning behaviour of the solar panels, while others have focused on the fire development in a field of six solar panels installed on an insulated roof and on a PVC roof.
Analysis of eight fires in six years
Eight fires involving solar panels on industrial flat roofs were identified. Those fires occurred over a five-year period (2016 – 2021). One further fire occurred but was insufficiently documented.
The distance between panels
Analysis of the fires shows that with rows of solar panels that are less than half a meter apart, the fire continues to develop over and under the panels, irrespective of the type of roof covering or insulation material.
Fire spread through the roofing
In most fires, the fire development has been limited to the area of the solar panels. Where the solar panels are burning and there is no ballast (in the form of gravel or tiles) on the roof, the roof covering will participate in the combustion and (regardless of the type of roof covering and insulation) the insulation will be damaged or participate in the combustion. Outside that area, the fire development is the same as on a normal flat roof and depends on the materials used.
Fire spread inwards
Openings or recesses in the roof surface, such as penetrations and skylights, can cause fire to spread inwards. This could have been the case in the fires investigated. The use of perforated roof sheets with acoustic insulation in PE bags provides insufficient fire resistance in such cases.
Fire development along cables
In a fire in the installation associated with the solar panels, regardless of the type of roof covering and insulation, the fire can spread along the cables to the solar panels and other parts of the building.
In none of the fires investigated did the fire spread beyond a fire-resistant partition.
Despite the current requirements for the solar power installation and subsurface on a commercial roof (inspection protocol SCIOS Scope 12 inspection), a fire can never be completely prevented. The Efectis analysis leads to recommendations that are differentiated according to prevention of fire development and prevention of fire spread, as follows.
Cause of fire in control cabinet/inverter
- Control cabinet on a non-combustible surface
A fire starting in a control cabinet can spread over the surface of the roof. The initial development can be limited by placing the cabinet on a non-combustible surface and the roof surface can be screened off around the box, using concrete tiles in both cases
- Fire-resistant facility for cable duct
As a result of a short circuit in the cables, the fire will almost always develop from the control cabinet in the direction of the solar panels. The cables must therefore be kept clear of the roof surface and a fire-resistant provision should be fitted between the cable duct and the roof surface, by placing the cable duct on a strip of concrete tiles, for example.
Cause of fire in the solar panels and the equipment under the solar panels
If a fire starts in the solar panels or the equipment under the panels, it is likely that the fire will spread unhindered over the solar panel field and that the roofing and insulation will be damaged, regardless of the type.
- Metal support structures
The use of plastics in the support construction of the solar panels should be avoided. Using metal support structures limits the development of the fire and the Building Decree would then allow a maximum of 5% plastic to be used in the support construction.
- Comply with test methods and standards
The NEN working group ‘Fire safety of PV panels in and on the building envelope’ is now trying to shed light on the relationship between the effect of a potential fire and the risk of this fire when a solar power system is added to a building, for which the Efectis research may be helpful.
In line with the current test methods, Efectis recommends that the roof construction at least complies with class Broof t1 in accordance with EN 13501-5, or with the classification of non-fire hazard in accordance with NEN 6063.
In addition, for The Netherlands, Efectis recommends applying the performance requirements of NEN 7250 – the standard for the integration of solar panels and solar collectors (solar boilers) in buildings – which, while not designated in the Building Decree, would meet the principles and requirements of safety and usability of structures.
- Ballast under solar panels
For a roof equipped with ballast, Efectis advises also installing gravel – or alternatively concrete tiles – under the solar panels in order to prevent radiation from the roof covering and to limit further fire development. Alternatively, a plate could be installed between the solar panels and the roof, preventing direct heat radiation to and flame contact with the roof covering.
Preventing and limiting fire spread
Fire spread inwards
- Distance between solar panels and transits and skylights
Regardless of the type of insulation used, inward propagation can take place via penetrations and openings in the roof plate and via skylights and rooflights. Efectis therefore recommends placing the solar panels at a sufficiently safe distance from them.
- Barrier with perforated roof sheet
Using a perforated roof sheet in combination with materials that melt during fire can create an open connection between the solar panels and the interior space, with the consequent risk of fire spreading inwards. In such a case, Efectis recommends installing a barrier that creates a fire-resistant roof, preventing the risk of fire spreading to the interior space. This could include installing a flame-proof plate between solar panels and the roof or fire-resistant cladding on the underside of the insulation or the roofing plate.
Fire spread to another fire compartment
None of the fires involved the spread of fire to another fire compartment, which can be prevented by using the usual fire-resistant partitions in a roof construction, for instance mineral wool and a strip of concrete tiles above the partition. For new construction situations, the width of the tile strip can be based on the provisions of NEN 6068.
The following additional studies could be considered:
- As there are very few fires on industrial roofs with solar panels, very little information is available. Knowledge about these fires would increase if fire research teams from the Fire Brigade, IFV and insurance claims experts were to collect and analyse more detailed information about such fires.
- Practical tests with different solar panels on various roof types to determine the fire development.
- Field tests in combination with heat radiation calculations to determine the safe distance between solar panels and openings in the roof.
Contact: René de Feijter – firstname.lastname@example.org