Barotrauma of the Mask
When a diver puts the mask on the surface, inside it is trapped a volume of air at the pressure of 1bar. After immersion, when reaching -10m, it is subject to an ambient pressure of 2bar. As through the regulator the diver breathes air to ambient pressure, it is equalling through the nose the pressure of the air contained in the mask, which is also at the pressure of 2bar. The mask is compensated.
However, if the diver starts the immersion without letting air out through the nose, when reaching -10m the ambient pressure will be 2bar but the pressure inside the mask will continue to be 1bar (the same pressure it brought from the surface). This creates an imbalance between ambient pressure and the air pressure contained in the mask. The mask was not compensated.
This imbalance of pressures results in the crushing of the mask against the diver’s face, causing a suction cup effect that gives rise to barotrauma. This suction cup effect produces a very painful symptom and can even cause the rupture of the capillary vessels of the eye. This rupture results in hemorrhages that affect not only the eyeball but also the surrounding tissues of the eye, signs sufficiently revealing of what happened.
THIS BAROTRAUMA ONLY TAKES PLACE ON DESCENT
The prevention of barotrauma of the mask passes through the insufflation of air into the mask through the nose , a maneuver that should be done as soon as the diver begins the descent.
If this maneuver begins to be done late, it may be impossible to inflate the air through the nose. In this case the diver should insert a finger under the edge of the mask to flood, thus restoring the balance of pressures, and then dry the mask by inflating air into it.