An Experimental Study of the Effect of Thermal Radiation Feedback on the Room Burning Behaviour of Horizontal Blocks of Polyurethane Foam

This report presents the results of three fire experiments (one free-burn and two room tests) that were carried out to investigate the influence of thermal radiation feedback on the rate of surface flame spread and heat release rate (HRR) for a horizontal block of furniture-grade non-fire-retarded polyurethane foam measuring 1200 x 600 x 200 mm and weighing approximately 4.8 kg.

The room tests were conducted in a small compartment measuring 2400 mm wide x 2800 mm deep x 2400 mm high with a rectangular vent (opening under a calorimeter hood) measuring 740 mm wide x 1500 mm high (a ventilation limit of approximately 2000 kW) located in one of the 2400 mm walls. The room was lined with one of two different non-combustible materials – 12.7 mm thick cement board or 50 mm thick mineral wool insulation – with substantially differential thermal inertias in order to subject the test specimen to one of two thermal environments.

Measurements were taken to quantify the temporal variation of heat release rates (HRRs), smoke density, radiant heat flux, temperatures and the concentration of O2, CO2 and CO in the test room. The tests were also recorded using an infrared camera in order to determine the surface rate of flame spread.

The free-burn peak HRR was found to be 498 kW at 172 s from ignition, plateauing at this value for approximately 34s before it rapidly declined. The peak HRR for the test conducted with a cement board room lining was 526 kW at 159 s from ignition (with immediate decline), while that for a mineral wool insulation lining was 965 kW at 176 s (with immediate decline).

The maximum room temperatures for the tests with cement board and mineral wool linings were 435 ℃ and 850 ℃, respectively. The results indicated that for the test with a cement board lining, there was no significant change in the peak HRR compared to the test conducted under free-burn conditions. Lowering the thermal inertia (with a mineral wool lining) resulted in a considerably greater (~ 90%) increase in peak HRR compared to the other two tests, which confirmed that radiation feedback from hot layer and walls was responsible for the dramatic increase in the peak HRR.

From the analysis of data record with an infrared camera, it was found that surface flame spread rates were higher (~ 12 mm/s) when the PUF was burning in the room than under free-burn conditions (~ 8 mm/s), regardless of the lining material used.