Tag: chemistry

In general, the stability of bromine in a typical flame retardant molecule means that the molecule can offer the highest activity as a flame active retardant, while also being cost effective.  The choice of flame retardant systems for any particular application depends on how the material decomposes in a fire, as well as the materials’ physical property. Brominated flame retardants, because they act in the flame, can be used in just about every application.

Carbon dioxide is heavier than oxygen. Due to this, carbon dioxide forms a blanket around the burning material and makes a barrier between the burning material and oxygen. As oxygen supply is cutoff, it helps in extinguishing the fire.

Water, when poured over fire absorbs large amount of heat and hence the temperature of wood falls below the ignition temperature. Thus the fire goes off.

Fire is extinguished by  :
(A) Removing all combustible substance. Fuel is one of the requirements for producing fire. In the absence of fuel, combustion will not occur.
(B) Cutting off a supply of air. Air (oxygen) is essential for combustion. In the absence of air, combustion will not occur.
(C) Cooling the burning substance. This reduces the temperature below its ignition temperature. The fire will not spread.

Fire can be extinguished by spraying, carbon dioxide, carbon tetrachloride or water.
Note:
Fire is extinguished by
(A) removing all combustible substance. Fuel is one of the requirements for producing fire. In the absence of fuel, combustion will not occur.
(B) cutting off the supply of air. Air (oxygen) is essential for combustion. In the absence of air, combustion will not occur.
(C) cooling the burning substance. This reduces the temperature below its ignition temperature. The fire will not spread.

Both options A and B describe the difference between fire extinguishing action of water and $CO _2$.

• Water helps to extinguish a fire in two ways: it cools the substance that undergoes combustion and brings the temperature of the combustible material below its ignition temperature. The water vapor formed due to the heat of fire surrounds the substance that undergoes combustion and cuts the supply of oxygen. 
  
• Carbon dioxide is highly volatile and it is heavier than oxygen. So, it immediately vaporizes to cut off the supply of air. In the absence of supporter of combustion, fire is extinguished. Also, it does not damage electrical equipment.
  

Some Class-B fires (hydrocarbons, petroleums, and fuels on fire) cannot be efficiently controlled with water. $CO _2$ being heavier than oxygen covers the fire like a blanket. Hence, one of the important factor for fire is cut off and the fire is controlled.

The ignition temperature of paper is lower compared to that of aluminium. When paper is wrapped around an aluminium pipe; the ignition temperature increases. That is why paper itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

The foam type of fire extinguisher is also called as soda acid fire extinguisher. It consists of dilute sulphuric acid and sodium bicarbonate (soda). When it is released under high pressure in the form of foam, it covers the surface of fire and controls it by cutting off oxygen.

Ignition temperature is the lowest temperature at which a combustible substance when heated (as in a bath of molten metal) takes fire in air and continues to burn. It is also called also autogenous ignition temperature.