ir and called the frontal, ethmoidal, maxillary, and sphenoidal, and come in pairs. The sinuses must be equalized just like the middle-ear space. Due to head colds, allergies, sinusitis, or smog, the sinus may become blocked, thus causing a sinus squeeze (Griffths 71-76). External squeezes are caused by the divers' equipment, such as the mask or wetsuit. When an equipment squeeze occurs, body tissues are pulled out and away Korell 7 from divers, rather than pushed into them. The mask squeeze, which may be the most common external squeeze, is caused by the inability to equalize the air pressure between the mask and the face on the diver's descent. To prevent a mask squeeze, the diver should exhale through the nose when suction is experienced on the face. A slow descent is also a way to help avoid this problem. A suit squeeze is another kind of squeeze to avoid. This is rare, but air pockets form between the suit and the skin and blood vessels on the surface of the skin could rupture. To prevent a suit squeeze, one must vent the suit of air and fill the former air pockets with water (Griffiths 76-78). The ascent is the same to the descent in relation to Boyle's law, but in the ascent, the surrounding pressure decreases, causing air pockets to expand. The two most common types of ascent problems are lung overexpansion and decompression sickness. In lung overexpansion, when a diver breathing compressed air returns to the surface, air in the lungs will expand due to the decreasing water pressure. A diver must breath regularly on the ascent in order to allow this reexpanding air to vent itself normally. Breath holding, uncontrolled ascents, or airway blockage could cause the expanding air to rupture the air sacs in the lungs, allowing air bubbles to enter the body and resulting in tissue damage, blood circulation blockage, or both. Lung overexpansion can be avoided through self-control. Divers should be able to perform a controlled ascent at ...
