ISBA

25 @the_isba Autumn 2021 | Environmental sustainability Fire can melt the roof anchors securing PV panels allowing them to cascade down the roof and a burning PV panel can release significant amounts of toxic gas. Another issue is the structural strength of the building; the roof may not have been fully assessed prior to installation and this could result in early roof collapse in the event of fire. To reduce the risks associated with solar voltaic panels you should: • Always use Microgeneration Certification Scheme (MCS) certificated installers. This should cover all stages of the operation – design, installation and maintenance. • Conduct periodic electrical safety checks to be completed by a qualified electrician in accordance with BS7671. The frequency of inspection/testing should be determined by risk assessment. • Always investigate the structural suitability of the building/roof. This not only needs to withstand the weight of the panels, but also any additional snow or wind loading. • Always ensure a DC isolating switch is installed and clearly labelled. Most new installations will include an AC isolating switch and this also needs to be clearly labelled. • Review and update Fire and Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) risk assessments for the building to reflect the presence of the panels. • Ensure you liaise with fire and rescue services on the location of panels and, in particular, isolation switches, when developing emergency plans. The emergency contact sheet should include contact details of the distribution network and the installers. Lithium-ion batteries A more recent trend is for PV to battery, where electricity generated by the PV system is stored in lithium-ion batteries within a building. In addition to the risks noted above, this also introduces lithium-ion batteries into the mix. These batteries can be volatile when exposed to heat or become damaged and can be difficult to extinguish when on fire. Short circuiting, overcharging, electrolyte breakdown and damage are the main reasons for lithium-ion battery failure. When a lithium-ion battery is exposed to heat there is a danger of thermal runaway (an exothermic reaction which cannot be stopped), this generates multiple explosions and flaming. At 70°C there is a danger of ‘cell burst’. The electrolyte fluid vaporises causing pressure increase that can burst the battery cell. At 130°C internal shortcut will occur causing temperature increase. At 150°C to 250°C thermal runaway will occur. This can be triggered by short circuit, overheating, over charging, deep discharge and mechanical damage. Toxic gas will also be released with just 1g of toxic gas capable of contaminating 48m³ of atmosphere. Unfortunately, there is currently no legal standard for PV to battery systems in the UK (it is under development). Mitigation measures to reduce the risks associated with storage include storing batteries in a dedicated fire compartment with at least 60 minutes fire resistance, fitted with a sill, explosion relief panels and ventilation extraction, much like a conventional flammable liquids store. Conventional fire detection in the form of smoke/heat detectors can be too slow to detect fires involving lithium-ion batteries as thermal runaway will already be in progress by the time of detection. Thermographic detection is better as it can pick up heat increases before the point of breakdown. Water in the form of sprinklers is the best form of extinguishment since it both cools and extinguishes, but water, foam or water with F500 encapsulating agent extinguishers can also be used. Biomass heating systems We have seen significant increases in the use of biomass heating systems in the education sector, including one independent school that uses biomass to heat more than 50 buildings. Biomass is the collective name for substances which have been grown, or derived from animal or vegetable matter, which can be used to generate energy. In the UK this is principally wood fuel (pellets, chips, logs). Biomass can be used to generate power, produce heat or used in combined heat and power plants. While biomass heating systems produce carbon dioxide when the fuel is burnt, the energy obtained from it is considered to be renewable since it releases CO 2 taken up from the earth’s atmosphere, over a short time-scale. Involve your insurer at the planning stage for any new sustainability project.