Page 51 - OHS, April 2020

to break down the fuel in gaseous components, and then oxygen reacts with the gas that is formed. The heat produced then breaks down more fuel into gases, and this cycle continues until one of the three components—oxygen, heat or fuel—is removed or consumed.
However, the chemical reaction that results in combustion is actually very complex and requires another component that we cannot observe. In order to react with oxygen, the fuel must break apart into highly reactive molecules called “radicals”. These radicals react with oxygen and form more radicals in a chain reaction that results in fire. Therefore, scientifically, fire requires four compo- nents: fuel, oxygen, heat and this chain reaction.
The Science of Flame Resistance
By using a deep scientific understanding of fire, fabric manufactur- ers have developed strategies for flame resistance that are focused on removing one of the components required to sustain the fire. All of these technologies are designed to snuff out a flame and mitigate the risk of injury for the wearer, but each of them has their own set of advantages. Since each of the technologies can be made perma- nent for the life of the protective garment and will not wash out with laundering, the selection of the technology will depend on the specific hazard and the preference for other attributes.
There is not a technology that is best for all hazard situations. For example, an electrical worker who may be exposed to an elec- trical arc flash hazard, a petrochemical worker who is exposed to the risk of flash fire and a firefighter who is exposed to a longer
duration fuel-fed fire may all require different technologies to their FR protective clothing. While taking into account industry require- ments, work environments, comfort and employee preferences, manufacturers create FR fabrics that are both tailored to thermal hazards that may be present on the job site and that offer consistent protection day-in and day-out.
There are three technologies that are commonly used to create FR fabrics: char-forming agents, gas-phase radical scavengers and high-temperature fibers.
Char-Forming FR agents
Char-forming agents are phosphorous-based fire retardants that can be incorporated into fibers or fabrics. They are primarily used with cellulose fibers such as cotton, rayon or lyocell. When these fabrics are exposed to fire, and the fibers begin to break down into gaseous fuel, the phosphorous agent reacts with the fuel molecules to form a stable, solid char. The char not only consumes the gaseous molecules, which would otherwise be fuel for the fire, but also cre- ates a barrier between the flame and the fabric and prevents the fabric from further breaking down and releasing more fuel. There- fore, these FR agents form flame resistant materials by depriving the fire of one of its four necessary ingredients, in this case, fuel.
These FR agents can be incorporated into synthetic cellulosic fibers during fiber formation or engineered onto fibers after fabric formation. The engineering process involves saturating the fabric with the phosphorous-based FR agent solution, and then conduct-
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