Certified Hyperbaric Technologist Practice Test 2026 – Comprehensive Exam Prep

To understand how 21% oxygen at 1 ATA (atmosphere absolute) is quantified in mmHg, it's essential to recognize that atmospheric pressure at sea level is approximately 760 mmHg. This represents the total pressure exerted by the air in the atmosphere.

When you want to find the partial pressure of a specific gas within a mixture (in this case, oxygen), you multiply the total atmospheric pressure by the fractional concentration of the gas. Since oxygen makes up about 21% of the air, this can be calculated as:

Partial pressure of oxygen = Total pressure x Fraction of oxygen

= 760 mmHg x 0.21 (where 0.21 represents 21%).

Calculating this gives:

760 mmHg x 0.21 = 159.6 mmHg.

This calculation illustrates how the partial pressure of oxygen is determined. In a hyperbaric environment, understanding these partial pressures is crucial, as they affect the therapeutic effects of oxygen therapy. The other options do not accurately represent the calculation needed to find the partial pressure of oxygen at 1 ATA, demonstrating that only this specific approach gives the correct value for the partial pressure of oxygen in this scenario.