CASE STUDIES

USE OF STUDIES

A review of the literature on the subject of Sandwich Panel fires, particularly related to reports in the popular press or media leads to several observations.  

 
1. In some cases, reports on Sandwich Panel fires fail to provide sufficient description of the construction details used and therefore it can be difficult to understand how representative, or typical, the construction was of either past practices or current day specifications and assembly methods.
2. Statements about the performance of Insulated Metal Panels are sometimes made by interested parties or manufacturers of particular core materials that only highlight the benefits of their product and the disadvantages of a competing product and in doing so perpetuate selective and sometimes contradictory views of product performance in the literature.
3. Insulated Panels do not cause fires and are rarely the first items ignited. Poor housekeeping practices and management of fire risk lead to fires which subsequently spread and expose the insulated panels.

COMBUSTIBILITY

The most common cores used in Sandwich Panel construction are EPS, Polyurethane Foam (PUR), Polyisocyanurate Foam (PIR) and Mineral Wool or Rock Fibre. EPS, PIR and PUR are all combustible. Mineral Wool Systems with combustible adhesives used to adhere the metal facings to the core are therefore combustible to some extent (but produce small amounts of energy in fire) as is Rock Fibre constituted with organic binders. However, the performance of the Panel Systems in fire and the extent to which the core contributes to fire spread, intensity and development, depends not only on the combustibility of the core but also on the behaviour of the Panel System as a whole and the degree and length of time for which the core is protected from the fire. Less combustible cores will of course have a reduced potential for the Panel to contribute to the fire, and this may or may not be significant depending on the nature of the initiating fire in the building and its contents.
It is agreed that Sandwich Panels do not start fires and they are rarely the item first ignited. There is also general agreement that the initiating fire needs to be sufficiently large before the Sandwich Panels have any significant impact upon the fire.

SPREAD WITHIN THE PANEL

A major concern in fire situations has been that fire may spread within the Sandwich Panel unseen. Opinion has been divided as to whether fire spread occurs in the growth stages of a fire and or once flashover has occurred and how much impact it has on the outcome of a fire. Research studies looking into ways to improve the performance of cored ISP specifically investigated the subject of fire spreading within the Panel's core. A 200mm by 200mm hole was cut in the 4,000mm (h) by 2,000mm (w), 100 mm thick cored ISP and then a gas burner (up to 300 kW) placed next to the hole for 60 minutes. The core of the ISP melted and burned where the fire impinged on the Panel and stopped burning once the flame/heat source was removed and did not propagate the fire spread by self-sustaining combustion through the core void (see Photo 1, 2 and 3). At a sufficient distance from the fire source, unaffected core remained.

These results have been confirmed by subsequent replicate testing commission by the EPSA Group, and testing by the CSIRO which found “there was no evidence of fire spread within the cores prior to flash over”. Previous research conducted by the University of Canterbury where a hot flue (max 8000oC) was placed flush against cored ISP, concluded that “flame-retardant EPS will not support self-sustaining fire spread in the insulated cavity of PIP when the core is exposed to a direct radiant heat source”.

TOXICITY OF ISP FIRE

An often cited concern is the “toxicity” of ISP when it is burning. The core, being a carbon based material will undergo combustion when a fire has reached a critical point, like all carbon based materials the products of combustion depending on the intensity of the fire and the level of oxygen available will be, carbon dioxide, carbon monoxide, soot, and a variety of other carbon based chemicals. Generally the most toxic chemical emitted from fires is carbon monoxide; the levels of this are directly related to the amount of oxygen available for combustion.

There is evidence that burning ISP is considered no a more toxic hazard than wood materials. The black colour of the smoke from burning polystyrene is indicative of the amount of unburned particulate material in the incomplete products of combustion building contents contribute to the smoke produced as well. Fires in buildings with few external openings will burn inefficiently and produce more soot and particulate matter if there is insufficient air available to ensure complete combustion of the fuel. Cool stores by their very nature have few external openings and therefore fully developed fires in those buildings are likely to be strongly ventilation controlled and exhibit incomplete combustion.