The human body needs constant gas exchange, inhalation of oxygen, exhalation of carbon dioxide, and maintenance of normal life activities. According to the scientific test, the amount of air per person is about 500 ml, and the amount of air to be inhaled per person per day is 12 cubic meters. About 22.6 liters of carbon dioxide is exhaled per hour. Oxygen accounts for 21% of air under normal conditions. When the oxygen content in the air drops to 12%, the human body may have difficulty breathing; when it is reduced to 10%, the mental activity may decrease; if it falls below 7% to 8%, it may be life-threatening. About 0.5 cubic meters of air per person is required per hour. Adults need about 500 liters of oxygen a day. An average of 21 liters of oxygen per hour.