Human beings breathe Oxygen and produce Carbon Dioxide as a normal biological function.

ALST Metabolic O₂ Consumption

It is normal to calculate the Metabolic O₂ Consumption as 0.5L / min per diver and to calculate the Metabolic CO₂ Excretion as 0.5L / min per diver. This is 1:1 exchange. This I consumption / excretion is affected by depth (so calculations DO NOT ALTER). These calculations work for exam questions, but in real life the true metabolic consumption varies dues to: body mass, work / rest and state of health.

You just need to remember that each diver consumes 720L of O₂ in a 24 hr period (0.5   x   60   x   24). Irrespective of depth or the volume of the system they are living in.

EXAMPLE

What is the metabolic consumption of oxygen of 3 divers at 75m³, What volume of O₂ will they use after 6 days?

Metabolic consumption is not affected by depth, so the 75m³ is irrelevant

0.5 litres per Min x 60 mins x 24 hrs = 720 litres per day

so 3 divers x 720 litres per day x 6 days ÷ 1000 (to convert to m³) = 12.96m³ of O₂

The ratio between O₂ consumption and CO₂ excretion is calculated as 1:1. With this knowledge we can also calculate the amount of CO₂ absorbent needed in a CO₂ scrubber. Therefore calculating the amount of soda-lime required in an ECU.

The amount of CO₂ absorbed with each brand varies (it is always written on the front of the container). For calculating purposes most it is established that: 6 kilograms / per-diver / per-day (regardless of depth) is used.

So 6kg is used in all calculations.

• IMCA D050-Minimum Quantities of Gas Required Offshore
• IMCA D022. Guidance for Diving Supervisors Manual, Chapter 2

TRY THE QUIZ >>>