July 2004. Location: Rotherham

Building description

The area associated with the fire was part of a development at the school nearing completion at the time of the incident. A passageway had been constructed to provide an escape corridor between the two flat roofs. The floor of the passageway was of concrete slab construction. Blockwork walls, that formed the corridors on the ground and first floors, had been carried to 1370mm above the concrete slab of the passageway thereby forming the lower walls of the passageway.

The upper walls of the passageway consisted of partitioning between the top of the blockwork walls and the underside of the insulated roof panels. The partitioning was constructed using a 70mm stud partition system consisting of metal studding fixed to the top of the blockwork wall. The top of the vertical studding terminated in an inverted ‘U’ channel that ran the full length of the roof. Fire resisting board, approximately 25mm thick, had been installed between the top of the inverted ‘U’ channel and the underside of the insulated roof panels.

The roof was constructed using insulated roof panels with a core of PIR (polyisocyanurate) approved to LPS 1181 Part 1. The insulated roof panels had not been cut into and the panels passed over the top of the partition system. Each side of the partition system had been clad with fire resisting board, approximately 15mm thick.

Fire

The fire was reported at 19.37 hrs when smoke was seen to be coming from the centre of the new roof section. From subsequent investigation it was believed that the fire occurred in a drum of roof sealant containing solvents that was accidentally or purposely ignited with a naked flame. The roof sealant was both the material first ignited; and the material mainly responsible for development of the fire.

The fire burned fiercely with flames impinging on the left hand blockwork wall, the partition and Insulated Panels above. Flame and hot smoke traveled down the passageway at high level in both directions.

The deformation of the purlins immediately above the seat of the fire shows that this was a very hot fire. The internal faces of eight roof panels in the immediate area of the fire had delaminated and deformed, exposing the insulation.

Observations

In spite of the substantial quantity of insulation exposed, there was no evidence that the insulation contributed to the spread of this fire; although it is probable that, while the fire was burning, the insulation charred and some smoke would have been produced.

From the physical evidence of the limited spread of heat and smoke to the roof void to the west of the passageway, it is clear that the general construction of the passageway and the partition system worked effectively as fire resisting barriers. There was only limited spread of heat and smoke between the top of the partition and the underside of the Insulated Panels. There was no evidence of heat or smoke spread through the insulation of the Insulated Panels.

Comments

The Insulated Roof Panels did not contribute to the cause of this fire. There was no significant involvement from the core material and no fire spread within the core despite exposure to the fire.