SSI Specialty Course Enriched Air Nitrox (SC-EAN) 40% Level 2 Practice Test

To determine the depth at which the partial pressure of oxygen exceeds 1.6 ATA for a gas mixture of Enriched Air Nitrox (EANx) with 40% oxygen, we first need to understand the relationship between depth, pressure, and the partial pressure of gases.

When you dive, the pressure increases by approximately 1 ATA for every 10 meters (or about 33 feet) of seawater. At the surface, the pressure is 1 ATA. Therefore, at depth, the total pressure (absolute pressure) is the sum of the atmospheric pressure plus the pressure from the water column above.

For EANx 40, which has 40% oxygen, we can calculate the partial pressure of oxygen at a given depth using the formula:

Partial Pressure of Oxygen (O2) = Total Pressure (ATA) × Fraction of Oxygen in the Mixture.

Setting the desired partial pressure of oxygen as 1.6 ATA, we can rearrange this to find the total pressure.

1.6 ATA = Total Pressure × 0.40 (since EANx 40 contains 40% oxygen)

From this, we can deduce that:

Total Pressure = 1.6 ATA / 0.40 =