NIST researchers explore one potential theory.
A mystery has raged for decades surrounding accounts of firefighters who receive steam burns through their protective clothing. One ruling theory is that the heat of the flames raises firefighters' own perspiration to the scalding point. But there’s a second potential culprit: water vapor that quickly penetrates firefighters’ protective suits and then condenses on their skin.
Firefighters’ protective clothing (FFPC) consists of three key layers of fabric: an outer shell made of a tough, light material, which serves as a first defense against flames; a middle layer that repels liquids on one side but allows perspiration to evaporate; and, closest to the skin, a quilted thermal liner for insulation.
But the suit's breathability is a two-way street, meaning vapor – water in its gas form – can enter. And burning buildings can actually be fairly damp environments, not only because firefighters are spraying water onto a blaze but also because water vapor is produced as part of the combustion process.
It has been unclear what role this vapor penetration plays in causing steam burns. In a series of exploratory experiments at NIST, researchers tried to determine how quickly the vapor could penetrate the protective fabrics, to see whether this issue should continue to be investigated.
To make their measurements, NIST researchers exposed swatches of the three-layer FFPC fabric to temperatures and humidity levels within the range experienced by firefighters. First, the team placed a sensor inside a thick insulated box with an open top. Then, they bolted the material samples over the box’s opening. Finally, they placed this sample box inside a metal humidity chamber about the size of a kitchen oven.
More work is needed to determine vapor penetration's role, if any, in a real firefighting environment. However, the team did find that when the sample box’s opening is covered by a material such as aluminum foil – which allows almost no gases to exit or enter – essentially no water vapor reaches the sensor inside. But when the test box is covered with the FFPC fabrics and exposed to the same temperature and relative humidity levels, the researchers detect, within minutes, water vapor that has reached a point where it could theoretically raise the temperature of skin.
If vapor penetration turns out to be a significant cause, the researchers hope their study could lead to new protocols to help firefighters decide how much time they can spend in a given environment before they risk getting steam burns. Future work could also inspire new design ideas for firefighters' protective clothing.