Fire safety Trisomet carries Grade EXT-B and EXT-A approval by the LPCB. It also achieves fire resistance performance of up to 4 hours integrity and 30 mins insulation dependant on panel thickness. These are attained using standard fixing and sealing methods (external side-lap stitched at maximum 300mm centres). The panel achieves a Broof (t4) performance for the external surface spread of flame and fire penetration on a roof in accordance with BS EN 13501-5. The internal surface of the panel also complies with a Class B s2 d0 rating in accordance with BS EN 13501-1.