Fire behaviour of insulated panels

External roof and wall panels
In the few fires concerning insulated panels used as the external envelope, involvement has only been at the fully developed stage of a fire. The majority of external roof and wall panels are manufactured with polyisocyanurate (PIR) or polyurethane (PUR) as the core material and about 10% with mineral fibre. Unlike internal sandwich panels, polystyrene is very rarely used.

PIR/PUR insulated panels do not burn, do not support fire spread and do not significantly contribute to the products of combustion. These facts are clearly illustrated in the Fire Case Studies into major fires in which PUR/PIR panels have become involved. See fire case histories.

The first affect of heat is to form a semi-protective char followed by a gradual reduction in thickness and as the fire develops will gradually decompose into gasses. PIR (polyisocyanurate) cores, as used in LPC or FM certificated panels, actually expand in the creation of the stable char and therefore fill any potential void caused by delamination of the face. Flames do not travel within the core between the facings even in the case of damaged panels.

All external panels including those with mineral fibre cores delaminate with heat due to the use of organic adhesives. However the structural integrity is maintained due to the secure method of fixing to the structural frame, thereby prohibiting collapse until the structure starts to fail. This point is now recognised by most fire services.

The ABI Technical Briefing on Sandwich Panels published in July 2003 supports the above comments on insulated panels used as the external building envelope. The document makes a number of important points in relation to external panels.

“There are far fewer instances of external envelopes being the cause of severe fire spread compared to insulated internal envelopes used for example to enclose food processing areas in food factories.”
ABI Technical briefing on sandwich panels – Section 3.3.1, page 5).

“Published fire statistics tend to show that external claddings constructed from sandwich panels are not a major fire risk, particularly if the chances of arson attack can be reduced and its effects minimised.”
ABI Technical briefing on sandwich panels – Section 4.1, Page 10.

“The fire services are in general less concerned where sandwich panels are used as the external roof and wall claddings, securely fixed to the structural frame of the building, since these do not present the same danger to life during fire-fighting.”
ABI Technical briefing on sandwich panels – Section 3.9, page 7).

These statements recognise the reality that there is very little evidence that external claddings of any kind contribute to fire losses.

Internal wall and ceiling panels
Most of the earlier and larger fires involved expanded polystyrene cored panels forming internal insulation walls in food industry premises. A relatively small fire can grow disproportionately particularly if the core is significantly involved or the panels collapse. Total losses have ensued. Whilst not all cores will react in precisely the same way, insurers now regard any site containing a high proportion of ‘non-certificate’ sandwich panels as being a potential total loss.

Since 2002 there have been significant changes in the securement of internal panels systems to ensure against collapse during the development stage of a fire. The use of insurance industry certificated panels have become the norm in food industry applications including the increasing use of PIR cored panels that do not burn or contribute to fire spread. See Certificated panels and testing.

Back to top. Also in this section:
Overview on insulated panels  |  Findings of fire research on major fires  | 
Fire research – case histories  |  Certificated panels and testing