Burning process
To understand the action of flame retardants, you have to understand the process of ignition and burning first. Fire is a reaction which takes place in the gas-phase. Thus in order for a substance to burn, it must become a gas first.
As with any solid exposed to a heat source experiences a temperature rise. If the temperature of the substrate is high enough, pyrolytic decomposition of the substrate will occur. The products of this decomposition include combustible gases, non combustible gases and char. If the combustible gases are mixed with enough oxygen from the ambient air; the gas/oxygen mixture ignites, yielding a flame, when its composition and temperature are favourable. Part of the generated heat will be transferred to the substrate to sustain the burning process.
Principle of flame retardancy
To ignitate a fire or keep the burning process alive; three items are necessary, the so called fire triangle:
- enough oxygen
- enough heat
- a burnable substrate
If one of these items is missing, a fire will not be ignited. Flame retardants are working on the principle to remove one or more parts out of fire triangle.
Examples
- Due to decomposition at certain temperatures, a flame retardant can produce non cumbustible gases. These gases will dilute the oxygen level of the ambient air. If the oxygen level will be below the minimum nessecary level (LOI- Limiting Oxygen Index) the fire will extinguish.
- A flame retardant can start an endothermic reaction if the temperature rises above a certain level. Due to this endothermic reaction, the substrate will cool and lots of heat will disappear.
More information
In the EFRA brochure "Flame Retardants Frequently Asked Questions" can be found more information about flame retardants and their different chemistries.
Download the EFRA brochure here:
EFRA_FAQ.pdf (0.8MB)