Compressed air is not just ordinary air. Compressed air is a concentrated stream of air at high pressure and high speed that can cause serious injury to the operator and the people around him.
Playing with compressed air can be fatal. In one case of an innocent attempt to frighten someone by suddenly blowing behind his back, the person was so surprised that he fell forward and was seriously injured on the moving parts of a machine. A misdirected jet of compressed air to the head can cause serious eye injuries or rupture the eardrum. Aiming the compressed air into the mouth can damage the lungs and esophagus. Careless use of compressed air to blow away dirt or dust from the body, even with a protective layer of clothes, could allow the air to enter the body, which can damage the internal organs.
The most serious damage that can be caused by compressed air occurs when air is blown in under the skin, for example via an open wound. It can lead to an air embolism, in which air bubbles are pressed into the veins and transported along the bloodstream. When the air bubble reaches the heart it causes symptoms similar to those of a heart attack. When the air bubble reaches the brain, it can cause a stroke. This type of injury can be directly fatal. Since compressed air usually contains small amounts of oil or dirt, severe infections can also occur if the compressed air enters the body.