Calculating the amount of gas a diver consumes is a vital part of many exams and life support.

ALST Gas Consumption

There are some standards you will always need to remember.

A diver working (surface supplied or by a bell) is calculated at 35L/min

Diver using bailout (so an emergency) is calculated at 40L/min. You also need to compensate for Helmet & Depth.

A chamber occupant on BIBS is calculated at 20L/min.

In the  Norwegian sector working & bailout is is calculated at 62.5L/min

EXAMPLE

A diver at 90msw has a bailout with a volume of 12 litre, and pressure of 180 bar. How much gas does he have?

Gas available = 12 litres x (180 – 10 – 10) (Note: less 10 bars hat / reg driving pressure, and another 10 bar for depth absolute) = 160 LITRES

So gas available = 12L x 160 bar = 1920 litres

Gas consumption = 40 litres per minute at the surface (Remember were on bailout)

At depth will be = 40 x 10 bar = 400 lpm

Duration = 1920 ÷ 400 = 4.8 (Note: The 0.80 is decimal. You now have to convert it) = 60 x 0.80 secs = 48

Therefore answer = 4 minutes 48 seconds

• IMCA D022. Guidance for Diving Supervisors Manual, Chapter 2, Section 7, Page 11

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