How do Flame Retardants Work?

shutterstock_211091626Do you enjoy sitting around a campfire and relaxing while you watch a log slowly burn? Can we blow your mind and offer that you aren’t really seeing the log burn? The fire phenomenon you are witnessing is a chemical reaction in which the fuel (wood) is being reduced to ashes because it is rapidly oxidizing in response to heat. The flame is the combustible gasses burning, as they are released from the log. Once the flames are visible there is a self perpetuation as the heat of the flames further heats the fuel, causing the fire to spread.

While the discovery of fire was a major turning point for our primitive ancestors, and in many ways is a huge asset, there is also the shadow side of fire that wrecks havoc and leaves a trail of destruction. Modern man has developed compounds used as flame retardants to help slow the spread of unwanted fire or more ideally cause self-extinction.

Understanding the context of fires and combustion makes the science behind flame retardants easier. Most people think solid materials burn—this is not true. Solid materials are decomposed by heat and release flammable gasses. When flammable gasses burn with oxygen, flames are visible. If solid materials do not get heated to the point of breaking down into gasses they smolder and usually self-extinguish, since there is a lack of flammable gas available to burn. 

There are three methods for flame retardance: vapor phase inhibition, solid phase char formation, and quench and cool systems.

1) The vapor phase inhibition approach to flame retardants aims to interrupt the radical gas phase of a fire. By disrupting the phase in which flammable gas is released the system is cooled and the supply of flammable gas is reduced or suppressed.

Bromine Flame Retardants (BFRs) are the most prolific flame retardant used for their vapor phase inhibition properties. Bromine in particular is used because as it is heated the compound releases active bromine atoms into the gas phase, before the material reaches its ignition temperature. These atoms quench the chemical reaction occurring within the flame and either extinguish the fire or slow the spread of the fire–such that there is increased escape time or increased time to attempt other means of fire extinction.

2) Solid phase char flame retardants are designed to build up the char layer, once the fire has begun. What is particularly interesting about the formation of char is it can have a two-fold benefit. It hinders the release of combustible gasses while also forming a protective layer that shields the underlying material from the heat of the flame. 

Melamine-based flame retardants are commonly used for their solid phase char functions. These flame retardant compounds fall into the category of nitrogen flame retardants. When in the condensed phase the molecule structures transform into cross-linked structures. That is when the transformation process occurs and char is formed.

3) Quench & cool systems utilize hydrated minerals because of the endothermic reaction that occurs when the system is heated. In the presence of fire, the hydrated minerals release water molecules that cool the polymer and interrupt the combustion process. In more simple terms, the release of water is chemically induced and the system is then cooled such that reactive gasses are not released and therefore cannot burn.

Aluminum and magnesium hydroxides are two compounds that interfere with the burning process through the release of inter gases (like water vapor). In this process a protective char layer is formed or energy absorption–the amount of energy available for the spread of fire–is reduced.

There are systems that combine multiple methods for achieving the ultimate in flame retardance. Each system must be carefully evaluated and analyzed for product safety and overall effectiveness. We regularly assist companies with identification quantitation of flame retardants. Contact us to discuss your unique needs and how we can be of service.

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