Dead space and snorkeling deaths on Maui

There were quite a few more than usual snorkeling drownings off the shores of Maui last year. Some of the newer full face masks for snorkeling may be to blame. Although the original models were quite close fitting in the face, clone models may have had enough dead space in the mask between the face and visor to explain passing out during their use leading to drowning.

What is dead space and how does it cause high CO2 pressures? As explained on this poster, we rely on almost completely emptying ourselves of the exhausted air we breathe out to prevent sucking carbon dioxide back into our bodies with our next breath. Too much re-circulation of exhaled air in a full face mask can defeat effective exhalation, allowing toxic levels of carbon dioxide to accumulate.