Answer:
c. In mines or confined places, where oxygen levels have been depleted, ventilation may occur.
Explanation:
Environments classified as “confined space” are hazardous for several reasons, but one of the main ones is the low oxygen concentration. Normally atmospheric air contains a 21% concentration of oxygen that is necessary for the maintenance of human life. Some confined spaces have this concentration of less than 21% oxygen, which can be very harmful to human life and lead to death.
Low oxygen concentration can be masked by ventilation in confined places. This is because in confined places oxygen levels may be low, but ventilation may continue despite inadequate oxygenation.