|Image from Du Pont.|
In between these layers is air. Air is a great insulator as the atoms are spread apart and it requires a lot of energy to have them increase their speeds (the electrons bouncing around) which in turn, transfers heat. When these layers become compressed the air is reduced, and even eliminated, allowing less of a buffer between the heat energy and the Firefighter inside. You may have seen or read about this in regards to compression burns on the knees of Firefighters as they advance hose lines or search. The air is not able to reduce the heat transfer and it is then allowed to penetrate quickly and interact with moisture inside the pants, causing a compression burn. A personal experience was similar. I was operating inside a burn can and I felt something like a knife cutting the side of my face. As it turns out my hood had slightly moved from my face and a bead of sweat traveled down just in front of my ear causing a burn. It only caused a minor inconvenience, but it sparked my curiosity of how the human body, PPE, and high temperatures all relate to each other.
Simply understanding that our bunker pants and coats have these layers, as well as the importance of the air layer, will start you down the path of understanding how critical using and wearing all your PPE is. This is not only true from a thermal protection standpoint, but from a carcinogen aspect as well. They buy it, you wear it! Look for more short snippets on how Firefighter turnout gear and the Firefighter interact in the months to come.
Learn more about superheated turnout gear and proper doffing by watching a great video by Frank Ricci and Justin McCarthy here - http://www.fireengineering.com/topics/m/video/31234087/doffing-superheated-gear.htm