Dive time is limited because the amount of gas in the cylinder is limited.
For safety, assume you will surface with 50 atm remaining.
The practical dive time can be estimated using the formula below.
The unit of volume is liter and the unit of pressure is atm.

1．Maximum depth ÷ 10 + 1 = Ambient pressure at maximum depth (atm)

2．Tank volume × (Start pressure − 50) ÷ Air consumption rate ÷ Ambient pressure = Practical dive time

◆◇◆ Question ◆◇◆

A diver with an air consumption rate of 30 liters/min dives to a depth of 20 m.
The diver uses a 12-liter tank filled to 200 atm and plans to surface with 50 atm remaining.

How many minutes is the practical dive time?

◆◇◆ Answer ◆◇◆

Tank volume: 12 liters
Start pressure: 200 atm
Maximum depth: 20 m

1．20 ÷ 10 + 1 = 3 atm (Ambient pressure at 20 m)

2．12 × (200 − 50) ÷ 30 ÷ 3 = 19.9 minutes

Therefore, the practical dive time is approximately 19 minutes.