Allegheny General Hospital in Pittsburgh gave the following explanation of the hyperbaric chamber treatment for mine survivor Randal McCloy Jr.:

In hyperbaric oxygen therapy, a patient is placed in a transparent airtight chamber at increased atmospheric pressure. The patient is surrounded by 100 percent oxygen, which circulates throughout the chamber. Normally we breathe about 20 percent oxygen and 80 percent nitrogen.

During treatment, pressure is increased up to twice the normal level. Oxygen is dissolved into the blood and all body tissues and fluids at up to 20 times the normal concentration.

Patients may experience the sensation of "fullness" in the ears, similar to the feeling experienced during flying. This is because the eardrums are responding to the change in pressure.

When oxygen begins to circulate, pressure or "compression" is gradually increased over a period of 15 to 20 minutes and maintained. When the chamber reaches the prescribed pressure, patients may rest or sleep; if healthy enough and conscious, they can even watch television or talk with family over an intercom. The treatment usually lasts 1 1/2 to 2 hours.

Near the end of treatment, pressure is gradually decreased over 10 to 15 minutes. During decompression, the ears may pop.

Patients usually experience no negative effects from the therapy, although they may feel lightheaded for a few minutes after treatment.