How Does Wood Fibre Perform In A Fire? – Can I Just Ask? – Ep.8

Wood fibre is a timber-based material and it does burn — that much is straightforward. What’s less well understood is how it burns and what that means in practice. In complete combustion, wood fibre produces very few harmful by-products and no significant toxic gases. Even in incomplete combustion, the outputs are well understood: carbon monoxide is the primary concern, and humanity has thousands of years of experience managing fire in timber structures. Compare that to PIR, which releases cyanide compounds in a fire, or certain mineral wool products which release hydrochloric acid gas when heated — both significantly more dangerous to occupants than anything wood fibre produces.

Wood fibre carries an E fire classification as an individual material, which on its own is not particularly impressive. But fire classification works on three levels: the material itself, as a wall or surface lining, and as part of a structural assembly. As a wall lining combined with other materials, BTE’s internal wall insulation systems achieve a B rating. As part of a structural build-up, timber and wood fibre assemblies can reach 90-minute fire ratings — comparable to many conventional systems, but without the toxic load. The charring behaviour of wood also provides genuine passive fire protection: the char layer that forms on the surface starves the combustion process of oxygen, slowing burn rate and in some cases causing self-extinguishment, while the structural integrity of the assembly is maintained for far longer than might be expected.

The broader point made in this episode is one that tends to get overlooked in discussions about non-combustible insulation. After any significant building fire, the structure almost always needs to be stripped back to its bare bones regardless of what insulation was used — non-combustibility doesn’t save the building. What it does affect is the toxicity of the environment during and after the fire: for occupants trying to escape, for firefighters working in the building, and for the fire investigation teams who work through the aftermath. Firefighters already experience cancer rates several times the national average, partly as a result of the synthetic compounds present in modern buildings. Specifying lower-toxicity materials where possible is a decision with real human consequences.