Oxygen gas is a supporter of combustion. It is used up during respiration, combustion and corrosion. So, if the proportion of oxygen in the air increases, the processes such as combustion, food digestion and corrosion will become very fast this would cause many problems. An increase in the proportion of oxygen in the air would lead to
(i) An uncontrollable rapid combustion of fuels. As a result, it would become extremely difficult to exstinguish fire.
(ii) An increased rate of metabolism in animals and human beings. This would result in an increased body temperature and increased appetite.
(iii) An increased rate of corrosion. This would result in early destruction of structures made of metals such as iron, copper etc.