Fuels are very useful for us. But there are certain disadvantages of burning fuels.

(i) Fuels like wood, coal, petroleum, etc. which are carbon fuels generally release unburnt carbon particles which are quite harmful. They cause various respiratory and skin diseases.

(ii) In most of the cases carbon dioxide is released during burning of fuels. This carbon dioxide is released in environment. This carbon increases the  temperature of the earth, which is called global warming.

(iii) Incomplete combustion of fuels release many poisonous gases like carbon monoxide in the environment. These poisonous gases create air pollution, such air if inhaled can be fatal.

(iv) Combustion of coal and diesel generates sulphur dioxide. It is a corrosive gas and it causes suffocation.

(v) Burning of petrol releases nitrogen oxides. These oxides of nitrogen and sulphur dioxide combine with rain water to cause acid rain. it affect aquatic life and natural environment.