Xiamen, China – When polyurethane foam burns, one of the safety issues is the flow and dropping behaviour of its liquid products. This can accelerate the fire’s growth, and help it to spread. Now, a team at Jimei University has looked more closely at this behaviour in the lab.
They found that when the foam is pyrolysed, the polyols at first form bead-like droplets on the surface of the foam. These subsequently change shape, from spherical to hemispherical and striped shapes on the outside of the foam, with the largest droplets having a downward flow velocity of about 5mm/s.
In contrast, any tiny droplets with diameters less than about 0.7mm actually float up. Any whose size is above the critical dropping diameter have a high risk of igniting any flammable materials below. This critical dropping diameter increases linearly with the height of the drop.
The scientists believe the additional insights their work gives into the behaviour of flexible PU foam as it burns may have important implications for the field of fire safety engineering.
The work has been published in the journal Combustion Science and Technology.