Using Phase Change Materials and Air Gaps in Designing Fire Fighting Suits: A Mathematical Investigation

Firefighting is a hazardous occupation that requires the wearing of appropriate protective clothing which must be designed to be flame- and heat-resistant while also allowing for a firefighter’s ease of movement. To increase the thermal protection provided by a firefighting suit and decrease the likelihood of the firefighter receiving skin burns, we propose incorporating a layer of a phase-change material (PCM) as well as air gaps in its structure. We investigate the distribution of heat through the layers of a firefighting suit and skin to determine whether this approach will be successful when different suit configurations are exposed to a range of fire scenarios with external heat fluxes between \(5\,{\rm kWm}^{-2}\) and \(84\,{\rm kWm}^{-2}\). We use a one-dimensional model of heat transfer which we solve numerically to determine the length of time each suit configuration allows a firefighter to be exposed to heated conditions before suffering irreversible thermal skin damage. Thermal damage to the skin is known to occur when the temperature in the basal layer exceeds \(44\)°C. Our earlier research indicated that the combination of air gaps and a PCM layer reduces the likelihood of skin burns, and that the most effective position of a PCM in a suit is near the outer layer. This current work considers a number of different PCM compounds for providing additional thermal protection while ensuring that the extra weight required is feasible for a firefighting suit. We found that of the PCMs studied, \({\rm MgCl_2\cdot 6H_2O}\) with an overall thickness of 0.17 mm gave the best improvement in the time until thermal skin damage (of between \(13\%\) and \(19\%\)), depending on the fire scenario.