Australia's Specialist Supplier of Industrial & Commercial Insulation Materials

Off-gassing from Fibrous Insulation

We have had a number of queries recently over the fumes given off from both rockwool and fibreglass when exposed to “high” temperatures. Here is the explanation why this happens.

Fibreglass & rockwool blankets, slabs & sections all contain a resin binder. The amount of binder varies from product to product. Generally speaking, the more rigid the product, the more binder will be contained in the product. It does not matter which company produces the material, product for product, the amount of binder will be similar. The higher the operating temperature that the product is exposed to, the more burn-off of binder will occur. Burn-off of binder from rockwool commences when the insulation reaches a temperature around 300C. Burn-off of binder from fibreglass / glasswool occurs when the insulation reaches a temperature around 175C.

In outdoor applications, the fumes generated by burn-off of binder mostly go un-noted. However in indoor applications, the sudden appearance of smoke can cause a degree of panic, as recently happened on one project where rockwool blanket had been installed on a co-gen exhaust pipe in a Sydney CBD building. After much discussion, and temporary suspension of system commissioning, it was accepted by all concerned parties that this was a normal occurrence. Commissioning was recommenced and burn-off ceased after about four hours.

It is recommended that all contractor customers point out the likelihood of burn-off occurring to their customers prior to commissioning of systems. To minimise or eliminate this problem with rockwool products, either use a wired mat product (wired mat tends to have less binder) or use a needled product such our cal-sil-mag fibre which has no binder. One of our contractor customers advises that on exhaust systems located on multi-storey sites he silicone-seals all cladding joints from the generator to the riser so that gasses do not escape into the plant room. The emitted gasses are classed as “nuisance fumes” but can cause running eyes & shortage of breath, so please exercise caution particularly in enclosed areas.