What is minimum gas?
Minimum gas is the gas two divers need to get from the deepest point to the surface on one tank, one of them with none, both breathing hard. Courses size it differently; the idea is the same. This episode works it out as rate × average pressure × time on one example dive, with the method of the written answer on the minimum gas page, and ends on a rounded table by the deepest point.
What is said
At the deepest point your buddy signals: out of gas. You share, and you both go up. How much must still be in your tank for that? That is minimum gas.
Minimum gas: the gas two divers need to get from the deepest point to the surface on one tank, breathing hard. Courses size it differently; the idea is the same.
Our example dive, at its deepest point, twenty metres: two stressed divers at twenty litres a minute each, from an eleven point one litre tank. The way up: a minute to sort out the problem, then three metres a minute on average. Step one, the rate: twenty litres a minute each, two divers. Forty litres a minute. Step two, the pressure: three atmospheres at twenty metres, one at the surface: add them and halve. Two atmospheres.
Step three, the time: twenty metres at three metres a minute, plus the minute at depth. Rounded up, eight minutes. Step four: rate times pressure times time. Six hundred and forty litres.
Step five, into bar: divide by the tank's litres. Fifty-seven point seven, rounded up to sixty bar: minimum gas for this dive.
Minimum gas is a floor under the plan: when either gauge gets there, the dive is over, whatever the plan said. By the deepest point, from a single aluminium eighty: forty, sixty and a hundred bar, rounded up, and never less than forty. Your course's figures come first.
Turn Pressure works out minimum gas for your dive, and the turn pressure. Free on the App Store. diver.today.