Time is of the essence
The risk of being engulfed by a flashover or backdraft during a fire fighter's career is minimal however fabric and garment manufacturers are continually working to engineer materials and garments that protect against this unlikely event.
Technical developments have resulted in fabrics containing a blend of Nomex® and Kevlar®, with the Nomex® content of the fabric providing heat and flame resistance. There are three distinct phases in the performance of Nomex®:
FLASHOVER - the garment is exposed to and absorbs significant heat, potentially 1000°c and causes the Nomex® fibres to swell and thicken, helping to eliminate conductive heat transfer and reducing heat transfer to the body. The outershell fabric and the level of protection remain intact and flexible.
ESCAPE - Nomex® remains supple and flexible until it cools, providing extra, crucial seconds of protection. In this phase break open does not occur. But all fire garments, regardless of their construction, will continue to hold the heat and so removal is critical to avoid burns caused by gradual conductive heat transfer.
RECOVERY - the outer garment is removed to allow both the fire fighter and the garment to cool down. During the cooling process the fibers that have absorbed heat solidify and subsequently if flexed they may crumble - sometimes referred to as 'break open'. This appearance is a clear sign that the heat has been absorbed and the garment has done its job to protect the fire fighter.
Further information: http://www.dpp-europe.com