Have you ever surfaced from a scuba dive with an indentation from your mask on your face? If so, you may have already experienced a mild mask squeeze. Serious mask squeezes are rare in scuba diving, but when they do happen, they can be painful and horrifying to look at. Thankfully, mask squeezes are completely preventable.
What Causes a Mask Squeeze in Scuba Diving?:
A diver's mask traps a pocket of air against his face (this is essential in order for him to see underwater
clearly). During descent, the air trapped behind the diver's mask behaves in the same manner as the air trapped in his other body air spaces. As a diver goes down, the pressure
surrounding him increases with his depth. The increase in pressure causes the air in his mask and other body air spaces to compress in accordance with Boyle's Law
. As the air compresses, it creates a pressure vacuum, or suction, on the diver's face. If the situation is not remedied, the suction can be so forceful that it damages the diver's facial tissues and eyes.
How to Identify a Mask Squeeze:
Mask squeeze affects a diver's eyes, cheeks, and forehead. A diver with severe mask squeeze may have inflammation and raccoon-like bruises over his cheeks and surrounding his eyes. Mask squeeze may also cause subconjunctival hemorrhages, or bleeding under the thin layer of transparent tissue covering the whites of the eyes. A diver who has experienced a mask squeeze may have bright red blood spots in the white of his eyes. His eyeballs may even be completely red (like a zombie!).
Equalizing a Scuba Mask to Prevent a Squeeze:
Preventing a mask squeeze is simple. A diver need only equalize the pressure in his mask as he descends by adding air to the mask's air space. To do this, a diver exhales into the mask from his nose, much as he would when clearing his mask of water. Many divers exhale small amounts of air through their noses without realizing it as part of their normal breathing cycle. These divers will not need to take any additional steps to equalize their masks. However, divers who have mastered "mouth only" scuba breathing will need to exhale into their masks periodically during descent. A diver should equalize his mask air space anytime he feels a slight suction on his face from his mask. Of course, it is best to prevent any pressure build up whatsoever, so a good rule of thumb is to exhale into the mask after each ear equalization.
No special action need be taken to equalize a scuba mask during ascent. The air inside a diver's mask will expand, just as the air in his other body air spaces. The expanding air will simply bubble out from under the skirt of the diver's mask, and does not present a problem.
Is Mask Squeeze Dangerous? What Is the Treatment?:
Mask squeeze is not usually dangerous and does not cause permanent damage. It is uncomfortable and embarrassing. Divers who experience a major mask squeeze, particularly a mask squeeze involving the eyes, should seek the advice of a doctor familiar with hyperbaric medicine. Antibiotic drops may be recommended for the eyes to prevent infection. A diver with an eye squeeze should expect the bright red color to slowly fade to green or yellow before disappearing, just as any other bruise would do.
The Take-Home Message About Mask Squeezes and Scuba Diving:
A scuba diver must equalize the air space inside his scuba mask during descent by exhaling periodically through his nose. Doing so will prevent the mask from suctioning onto his face, which can cause bruising of his cheeks, forehead, and eyeballs. A mask squeeze is not a serious injury, but may require antibiotics to prevent an eye infection. Interestingly, the likelihood of a facial squeeze is the reason that a diver may not use standard swim goggles while scuba diving. Swim goggles do not cover a diver's nose, making them impossible to equalize.