How Do We Control Fire?
key notes :
Controlling the Fire
Generally, water is used to control fire. Water brings down the temperature of the combustible substance below its ignition temperature. The water vapour surrounds the combustible material, thus helping in cutting off the supply of air. So, that the fire is extinguished.
Fire produced by the burning of oil or petrol cannot be controlled by throwing water on it because water being heavier than oil, settles down the oil and oil continues to burn
We know that there are 3 conditions necessary for producing and sustaining combustion.
- Presence of a combustible substance.
- Presence of a supporter of combustion.
- Attainment of ignition or kindling temperature.
Thus, fire can be controlled by removing one or more of these requirements of fire control.
Fire Brigade
- Many times homes, forest, shops, etc. catch fire. In such cases, it becomes necessary to put off the fire otherwise, it may cause huge monetary loss and loss of lives.
- Fire Brigade or Firemen are experts in controlling fire by using a fire extinguisher. To extinguish the fire, at least one out of three essential conditions for combustion must be removed. Supply of fuel, supply of air and ignition temperature are the three essential conditions for combustion.
- In case of fire in a building, the whole building becomes fuel. It is not possible to cut off the supply of fuel. Thus, firemen try to cut off the air supply and or bring down the temperature of combustible material below their ignition temperature.
Fire Extinguisher
- Water is one of the best, cheapest and oldest fire extinguishers. By pouring water over the combustible material, the temperature can be cooled down. Cooling down brings the combustible materials below their ignition temperature.
- In addition to this, water vapour surrounds the combustible material which stops the supply of air. Removal of these two conditions puts off the fire. This is the cause that firemen generally pour water over the materials which have caught fire.
1. Controlling fire when electrical equipment is on fire
- Water is not suitable in the case when electrical equipment or oil catches fire.
- In the case of electrical equipment on fire, pouring water over them may prove disastrous because normal water is a good conductor of electricity.
- It may conduct electricity and can harm the persons who are trying to control the fire.
2. Controlling fire in the case of oil, petrol, etc.
- Water is heavier than oil. So when water is poured over oil. It comes on top and keeps on burning. In such cases, a fire extinguisher is used.
3. Carbon dioxide as a fire extinguisher
- Carbon dioxide does not support combustion and hence is considered the best fire extinguisher.
- Carbon dioxide is heavier than air and hence covers the material which is burning. By covering the material, the supply of oxygen is stopped. This puts off further combustion and fire is controlled.
- Under high pressure, carbon dioxide liquefies and takes less space because of compression. Liquid carbon dioxide is stored in cylinders.
- A nozzle is attached to the cylinder to release carbon dioxide. When the nozzle is opened, carbon dioxide starts coming out from the cylinder because of high pressure. It expands and covers the combustible materials as a blanket.
- This cuts off the supply of oxygen to combustible materials. Because of expansion, the temperature of carbon dioxide decreases which decrease the temperature and brings down the combustible material below their ignition temperature. Thus, the stoppage of the supply of oxygen and bringing down the temperature below the ignition temperature of combustible materials put off the fire.
4. Sodium bicarbonate or potassium bicarbonate as a fire extinguisher
- Sodium bicarbonate (baking soda) or potassium bicarbonate releases carbon dioxide on heating.
- Thus, when powder of sodium bicarbonate or potassium bicarbonate is spread over or near the fire, they release carbon dioxide which covers the burning materials and cuts off the supply of oxygen to them. This puts off the fire.
Let’s practice!
