Breathing pure oxygen at atmospheric pressure does not present any problems unless it is continued for several hours. Under these conditions, there is there is only a slight increase in the partial pressure of oxygen in blood.
However, if pure oxygen is breathed at high pressures, its partial pressure in blood increases considerably due to a sharp increase in its solubility in plasma. in an attempt to utilize the extra oxygen, tissues metabolize very fast utilizing carbohydrates, lipids and proteins ”literally burning the tissues”.
The situation is worsened by the accumulation of carbon dioxide which stimulates the respiratory and circulatory system to work harder leading to the impairment of special senses especially vision and hearing followed by dizziness, convulsions and death.
These can be major drawback or impediment with locally made ventilators in the fight against Covid-19.