The harmful effects of burning fuels:
(i) Fuels like wood, coal, petroleum etc. which are carbon fuels, produce unburnt carbon particles, which cause respiratory diseases (asthma) and skin diseases.
(ii) Generally CO₂ is released during burning of fuels. It causes the rise in the temperature of the atmosphere of earth, which is called global warming.
(iii)Incomplete combustion of fuel releases many poisonous gases such as carbon monoxide. It can kill people sleeping in a room by causing suffocation.
(iv) Combustion of coal and diesel generates sulphur dioxide. It can kill people sleeping in a room by causing suffocation.
(v) Burning of fuels releases oxides of nitrogen and sulphur. They dissolve in rain water and form acid. Such rain is called acid rain. It is harmful to crops, buildings and soil.

Three essential requirements to produce fire are as follows:
(i) Fuel
(ii) Air and
(iii) Heat to acquire the ignition temperature. The job of fire extinguisher is to cut off the supply of air or to bring down the temperature of fuel or both. The most common fire extinguisher is water. But water works only when things like wood and paper are on fire. For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (C0₂) is the best extinguisher. CO₂ being heavier than oxygen, covers the fire like a blanket. Since, the contact between the fuel and oxygen is cut-off, so the fire can be controlled. The added advantage of CO₂ is that in most cases, it does not harm the electrical equipment.

Reasons of forest fires are
(i) At high temperature, sometimes dry grass catches fire which spreads throughout the forest.
(ii) Campfire may also be a reason.
(iii) Lightning.
(iv) The use of fires by villagers to ward off wild animals.
(v) Fire lit intentionally by people living around forests for recreation.
(vi) Fires started accidentally by careless visitors to forests how discard cigarette butts.
(vii) The friction of bamboos due to high wind velocity and rolling stones.

We have to use paper or kerosene oil to start fire in wood or coal. It is because coal has high ignition temperature. A burning matchstick cannot produce sufficient heat to reach the ignition temperature of coal. Since, ignition temperature of paper or kerosene oil is low, so if some kerosene is sprinkled over the wood, the kerosene starts burning by a lighted matchstick. The heat produced by the burning of kerosene makes the wood to burn. The coal pieces are then placed over the burning wood. The large heat produced by the burning wood heats the coal to its ignition temperature. In this way, the coal starts burning.

Solid fuels Examples are wood and coal. These are used to cook food in homes. Coal is also used in industries.
Liquid fuels Examples are kerosene and petrol. Kerosene is used in stoves and in lamps to cook food and petrol is used as a fuel in automobiles.
Gaseous fuels Examples are natural gas and petroleum gas. These are used in industries, CNG is used to run automobiles.

It is because
(i) Charcoal burns easily as compared to wood.
(ii) Charcoal does not produce smoke on burning and so, it causes no air pollution.
(iii) The amount of heat produced by burning charcoal is much more than that produced by burning of wood.

Pouring water to extinguish the fire due to oil was not suitable action. It is because oil is lighter than water. So, water will settle down below the oil. In such condition, sand or soil should be used. They cut off the supply of air to the fire. Thus, fire can be controlled. But sand or soil will not be available at that place. So, Manu should have switched off the flame of the burner and put a lid on the frying pan. By doing this, the contact between fuel and oxygen is cut off and the flame will go off.