Environmental chemistry is a crucial area within Chemistry Topics that examines the impact of chemicals on the environment and seeks to understand their behavior and effects.
Write a Short Note on History of Matchstick and How to Control Fire
A short, thin piece of wood having chemicals coated at one end, which is used to light a fire by rubbing against a rough surface, is called matchstick. The history of matchstick is very old. About 5000 years ago, small, thin pieces of pinewood dipped in sulphur at one end, were used as matchsticks in ancient Egypt. The modern safety match (or matchstick) was developed only about 200 years ago.
Earlier, a mixture of antimony trisulphide, potassium chlorate and white phosphorus with some glue and starch was applied to the head of a matchstick made of suitable wood. When the head of this matchstick was rubbed against a rough surface, white phosphorus got ignited due to the heat of friction.
This started the combustion (or burning) of matchstick. White phosphorus is poisonous. So, the use of white phosphorus in making matchsticks proved to be dangerous for the workers engaged in making matchsticks as well as for the users.
These days, the head of matchstick (or safety match) contains only antimony trisulphide and potassium chlorate. The rough rubbing surface on the side of the matchbox has a coating of powdered glass and a little red phosphorus (Red phosphorus is much less dangerous than white phosphorus).
When the matchstick is rubbed against the rough surface of matchbox, some red phosphorus is converted into white phosphorus. This white phosphorus immediately reacts with potassium chlorate in the matchstick head to produce sufficient heat to ignite antimony trisulphide and make the matchstick head burn. We will now describe how to control unwanted fires.
How Do We Control Fire
Burning (or combustion) produces fire. Fire is useful as well as harmful. We make small fire in a gas stove to cook our food. This is a useful fire. Without fire, we cannot cook our food. But when a fire breaks out in a house, an office, a factory, an oil tanker, a petrol pump or an electrical equipment, then the fire is harmful. It can cause loss of life and property. Such fires must be brought under control and extinguished at the earliest. The process of extinguishing a fire is called fire-fighting.
Every city and town has a Fire Service in the form of Fire Brigade Station. The fire-fighters of Fire Brigade specialise in putting out fires. All of us should know the telephone number of the Fire Service of our city. The telephone number of Fire Service in Delhi is 101.
God forbid, if a fire breaks out in our house or in our neighbourhood, we should at once call the Fire Service. We should also know how fire is caused and what are the different ways of fire-fighting or putting off fires. This is discussed below.
Any fire needs three things to be present: Fuel (Combustible substance), Air (or Oxygen) and Heat. If any one of these three things is removed, then the burning will stop and fire will be extinguished. Thus, a fire can be extinguished in three ways :
- By removing the fuel (combustible substances)
- By removing the heat (by cooling with water)
- By cutting off the air supply to the burning substances (with carbon dioxide, etc.)
We will now discuss these three ways of extinguishing fire in detail, one by one.
1. Remove the Fuel (or Combustible Substances)
A fuel (or combustible substance) is a food for fire. So, when fire starts in a room, all the combustible substances like furniture, clothes, and books, etc., (which can burn easily) should be removed at once so that fire may not spread. If possible, cooking gas cylinder should be removed and electricity should be switched off. If the fire is near a pile of wood that could provide fuel to keep the fire going, the pile of wood should be removed from there as soon/as possible. It is, however, usually not possible to remove all the combustible materials from the place of fire.
2. Remove the Heat
Water is used to remove heat from a burning substance and to make it too cool to burn further. Water is the most common fire extinguisher for ordinary fires. Water extinguishes fire by cooling the burning substances. When water is thrown on a burning substance, it gets cooled below its ignition temperature and stops burning. The fire gets extinguished.
For example, when fire brigade man throws a strong stream of water on a building on fire, the burning materials get cooled to below their ignition temperatures and fire is extinguished. The water vapour produced by the action of heat of fire on water surround the burning material and help in cutting off the supply of air. This also helps in extinguishing fire.
Thus, fire-men extinguish the fire by throwing water under pressure on the burning things such as houses, factories or other buildings. Water works as a fire extinguisher only when things like wood and paper, etc., are on fire. The fires caused by burning oil (or petrol) or those caused by electricity, however, cannot be extinguished by using water. This is explained on the next page.
The fire produced by burning oil and petrol (like fire in frying pan, oil tanks, petrol pumps and airports, etc.) cannot be extinguished by using water. This is because of the following reason : Water is heavier than oil and petrol. So, when water is thrown over burning oil (or petrol), it (water) settles down. The oil (or petrol) floats on water and continues to burn. Thus, fires caused by burning oil (or petrol) cannot be extinguished by pouring water over it.
The fires caused by electrical short-circuit in an electrical appliance or in electric wiring should not be extinguished by throwing water. This is because of the following reason : Ordinary water conducts electricity to some extent. So, when water is thrown over the burning electrical appliance (or burning electric wires), it can give electric shock to the persons involved in fire-fighting. Thus, water cannot be used to extinguish fires caused by electricity.
3. Cut Off the Air Supply
Many fires can be extinguished by cutting off air supply to the burning substances. The air supply to a burning substance can be cut off in a number of ways such as covering the burning substances with carbon dioxide, sand (or soil), a blanket or a damp cloth, etc.
The electrical fires are extinguished by using carbon dioxide gas fire extinguisher. Carbon dioxide gas is denser than air and forms a layer around the burning substances. Carbon dioxide layer covers the fire like a blanket due to which fresh air cannot reach the burning substances. The burning substance does not get oxygen of air and hence stops burning. In this way, the fire gets extinguished.
Please note that carbon dioxide gas neither burns itself nor supports burning (or combustion). An added advantage of carbon dioxide is that it does not harm the electrical equipment. The fires caused by the burning of inflammable materials like oil or petrol are also extinguished by using carbon dioxide fire extinguishers.
Carbon dioxide used for extinguishing fire can be stored as a liquid at high pressure in cylinders (called fire extinguishers). When released from the cylinder, carbon dioxide expands enormously in volume and cools down. In this way, carbon dioxide not only forms a blanket around the burning substance, it also cools down the burning substance.
This makes carbon dioxide an excellent fire extinguisher. Another way to obtain carbon dioxide for extinguishing a fire is to release a lot of dry powder of chemicals like sodium bicarbonate (baking soda) or potassium bicarbonate over the fire. The heat of fire decomposes these chemicals to produce carbon dioxide gas. And this carbon dioxide then extinguishes the fire.
A small fire can be extinguished by throwing sand (or soil) over it. For example, when sand is thrown over burning kerosene oil, the sand covers it like a blanket. The sand cuts off the air supply to the burning kerosene oil due to which the fire gets extinguished. The cooking oil fire in a frying pan in the kitchen can be extinguished by covering the pan with a fire blanket or a damp cloth.
When the frying pan is covered with a fire blanket or a damp cloth, the supply of air to the burning cooking oil is cut off and hence the fire gets extinguished. If the clothes of a person working in the kitchen catch fire, the person is immediately covered with a blanket. When the burning clothes of a person are covered with a blanket, the supply of air to the burning clothes is cut off and hence the burning (or fire) stops.
Types of Combustion
There are various types of combustion. The three important types of combustion are:
- Rapid combustion,
- Spontaneous combustion, and
- Explosive combustion (or Explosion).
We will now describe these three types of combustion reactions in a little more detail, one by one.
1. Rapid Combustion
The combustion reaction in which a large amount of heat and light are produced in a short time is called rapid combustion. When we bring a lighted matchstick or a lighter near the burner of a gas stove in the kitchen, the cooking gas starts burning at once producing a lot of heat and some light. So, the immediate burning of cooking gas (LPG) in a gas stove to give heat and light, is an example of rapid combustion.
The burning of kerosene oil in a kerosene stove and the burning of wax in a candle are also examples of rapid combustion.
2. Spontaneous Combustion
The combustion reaction which occurs on its own (without the help of any external heat), is called spontaneous combustion. In spontaneous combustion, the substance suddenly bursts into flames and starts burning (even without being heated). Spontaneous combustion takes place at room temperature. The heat required for spontaneous combustion is produced inside the substance by its slow oxidation.
Spontaneous combustion is usually undergone by those substances which have quite low ignition temperatures. White phosphorus is a substance which undergoes spontaneous combustion. In other words, white phosphorus burns in air at room temperature. So, if we keep a piece of white phosphorus in a china dish, we will see that it catches fire by itself and starts burning (without being heated).
The burning of white phosphorus on its own at room temperature is an example of spontaneous combustion. The heat required to start this spontaneous combustion is produced internally by the slow oxidation of phosphorus in air.
The spontaneous combustion reactions which take place in nature are very dangerous. For example, the spontaneous combustion of coal dust has resulted in many disastrous fires in coal mines (leading to the death of many persons working in deep coal mines). Forest fires can also be started by spontaneous combustion reactions.
Sometimes, due to the heat of the sun (or due to the spark of lightning from the sky), spontaneous combustion of straw and forest wood takes place leading to forest fires. Most of the forest fires are, however, caused due to the carelessness of human beings.
When human beings throw away lighted cigarettes in the forest or leave behind a burning campfire after having a picnic in the forest, then forest fires are started. It is, therefore, important that burning cigarette butts, etc., are not thrown in the forest, and campfires are completely extinguished before leaving the forest after a visit.
3. Explosive Combustion (or Explosion)
A very fast combustion reaction in which a large amount of heat, light and sound are produced, is called explosive combustion (or explosion). A large amount of gases is released quickly in an explosive combustion. It is the rapid expansion of these gases which causes a loud sound (or explosion).
The fireworks (crackers, etc.) which we explode during festivals work on the explosive combustion of substances. When a cracker is ignited with a burning matchstick, the chemicals present in it undergo a sudden (very rapid) combustion producing heat, light and a large volume of gases.
The gases produced are heated by the heat evolved in the reaction. The hot gases expand rapidly and cause an explosion (producing a loud sound). Explosive combustion (or explosion) can also take place if pressure is applied on the cracker by hitting it hard.