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What Should I Do If I Must Vomit Underwater?:

1. Do Not Remove Your Regulator.
After vomiting, a person will reflexively gasp for air. If a diver removes his regulator to vomit, he may not be able to replace it in time and may inadvertently inhale water. Instead, a diver should hold his regulator in his mouth and vomit into the regulator mouthpiece. This will not contaminate his air supply – the vomit will exit through the one-way exhalation valve. The first breath after vomiting should be taken as carefully as possible, ensuring that any leftovers do not get inhaled.

2. Purge the Regulator If Needed.
After vomiting, a diver can use the regulator's purge button to flood the regulator second stage with air and force any leftover debris out the exhaust valves. A diver purging the regulator after vomiting should take care to place his tongue over the regulator mouthpiece while pressing the purge button, so that any remaining vomit does not get blown back into his mouth.

3. Be Prepared to Switch to the Alternate Air Source.

Depending upon a diver's last meal and chewing habits, vomit may be of different consistencies. If a diver is unlucky enough to have the chunky variety, pieces of puke could become lodged in the regulator mouthpiece and cause it to free-flow or malfunction. This is what alternate air source regulators are for! (They are also useful if breathing from a recently puked in regulator simply disgusts you). If a diver does switch to his alternate air source, he should end the dive because diving without an alternate air source regulator available for his buddy is unsafe.