If air supply is contaminated by 1% carbon monoxide at 66 feet, this is equivalent to what percentage at sea level?

When diving, the effects of pressure must be considered in relation to the composition of air. At sea level, the atmospheric pressure is approximately 1 atmosphere (atm), but at a depth of 66 feet, the pressure increases due to the weight of the water above the diver. Specifically, 66 feet of seawater adds about an additional 2 atm of pressure, making the total pressure at that depth roughly 3 atm (1 atm from the atmosphere above water plus 2 atm from the water itself).

When calculating the equivalent contamination level of carbon monoxide at a higher pressure, it is important to understand that the partial pressure of a gas increases as the total pressure increases. If the air supply is contaminated by 1% carbon monoxide at 66 feet, this percentage refers to the proportion of carbon monoxide in the ambient air at that pressure.

To find the equivalent percentage at sea level, you can consider the fact that the amount of carbon monoxide present at a higher pressure will feel more concentrated due to the increased total pressure. The relationship can be expressed as:

Percentage of CO at depth = Percentage at surface × (Total pressure at depth / 1 atm)

So, if we multiply 1% CO by the total pressure at 66 feet (