The thermal criteria on rubber ignition in flashover fires under longitudinal ventilation surroundings

Abstract

Flashover tests and theoretical analysis were conducted in a test chamber with two openings under longitudinal ventilation conditions with rubber as the target fuel. The radiant heat flux to the floor, the mass loss rate of fuels, the upper hot smoke layer temperature, the oxygen and smoke composition concentrations were measured to identify the thermal critical criteria of rubber ignition. The up-wind rubber sample was early ignited by the ∅500mm alcohol under 0.1m/s surroundings at the radiant heat flux to the floor 15.17kW/m2 and the average upper hot smoke layer temperature 519°C. The ∅500mm diesel of thick sootiness ignited the rubber earlier at a lower average upper hot smoke layer temperature 409°C and a higher radiant heat flux to the floor 16.2kW/m2. The rubber cannot be ignited by the ∅500mm alcohol or diesel at 0.5m/s smoke discharge velocity. It is concluded that the radiant heat flux to the floor is the predominant point to rubber ignition. The longitudinal smoke discharge can restrain the ignition of rubber in flashover by the dramatic reduction of the radiant heat flux to the floor based on the increased convection heat loss and the decreased smoke sootiness.