Saturday, April 26, 2014

PPE Layers

Today's structural turnout gear enables the firefighter to get up close and personal to the heat, smoke, and flames during an interior fire attack. A few of the first concepts Firefighters learn during the initial fire behavior course are the methods of heat transfer. Basic laws of thermodynamics state that heat(energy), as a process, moves by conduction, convection, and radiation. Conduction is object to object transfer of energy. Convective heat transfer is gas movement, and of course radiation is light waves. Understanding how the energy of a compartment fire moves throughout the container, along with the capabilities and limitations of structural PPE, will ensure Firefighters operating inside maintain appropriate posture and position during a fire fight.

Image from Du Pont.
A key element in achieving a higher understanding of how to conduct business inside of a structure, during fire control evolutions, is recognizing what the gear we wear actually does for us. Several layers make up the total package for Firefighter protection. The outer most layer protects the wearer from cuts, abrasions, and the "stuff" we may run into during fire control or search. The next layer is the moisture barrier which keeps liquids such as water, oils, and others out. Thermal protection comes from, which is quite interesting, the innermost layer. Several manufacturers boast that 50% of the total thermal protection comes from this inner layer. Small percentages of the outer layers do protect the user from heat, however this inner thermal layer provides protection from thermal energy transfer. Could more thermal protection be constructed to provide more protection? From what I understand the answer is yes, but that creates more stress on the body. Current protection factors seek to create an equilibrium of protection and heat dissipation of the user.

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 -