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How do flame retardants work?

Q: How do flame retardants work?

A: Flame retardants are added to different materials or applied as a treatment to materials (e.g., textiles, plastics) to prevent fires from starting, limit the spread of fire and minimize fire damage. Some flame retardants work effectively on their own; others act as “synergists” to increase the fire protective benefits of other flame retardants. A variety of flame retardants is necessary because materials that need to be made fire-resistant are very different in their physical nature and chemical composition, so they behave differently during combustion. The elements in flame retardants also react differently with fire. As a result, flame retardants have to be matched appropriately to each type of material. Flame retardants work to stop or delay fire, but, depending on their chemical makeup, they interact at different stages of the fire cycle. To better understand how flame retardants work, it’s helpful to understand the fire cycle:

  • Initial ignition source can be any energy source (e.g., heat, incandescent material, a small flame).
  • Ignition source causes the material to burn and decompose (pyrolysis), releasing flammable gases.
  • If solid materials do not break down into gases, they remain in a condensed phase. During this phase, they will slowly smolder and, often, self-extinguish, especially if they “char,” meaning the material creates a carbonated barrier between the flame and the underlying material.
  • In the gas phase, flammable gases released from the material are mixed with oxygen from the air. In the combustion zone, or the burning phase, fuel, oxygen and free radicals combine to create chemical reactions that cause visible flames to appear. The fire then becomes self-sustaining because, as it continues to burn the material, more flammable gases are released, feeding the combustion process.
When flame retardants are present in the material, they can act in three key ways to stop the burning process. They may work to:
  • Disrupt the combustion stage of a fire cycle, including avoiding or delaying “flashover,” or the burst of flames that engulfs a room and makes it much more difficult to escape.
  • Limit the process of decomposition by physically insulating the available fuel sources from the material source with a fire-resisting “char” layer.
  • Dilute the flammable gases and oxygen concentrations in the flame formation zone by emitting water, nitrogen or other inert gases.

“Flame Retardants.” Flame Retardant Basics, 

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