Dive Calculators

Below are a few interesting calculators that attempt to explain a little about diving physics. WARNING: These calculators are to be used for informational purposes only and not to be used for dive planning.

Charles Law

Charles' Law states:

"For any gas at a constant pressure, the volume of the gas will vary directly with the absolute temperature or for any gas at a constant volume, the pressure of the gas will vary directly with the absolute temperature."

Ever get a quick or "hot fill" at the dive shop only to find that when you check the pressure at the dive site it's well below what you would have expected? This is the result of Charles' Law. As the rate in which air is pumped into a cylinder increases so does the temperature of the cylinder. As the temperature of the cylinder decreases so does the volume of air. Below is a pressure and temperature calculator which demonstrates this theory. Enter in the starting cylinder temperature and the pressure after the fill. Next enter the cylinder temperature at the dive site. The result will be the actual pressure before you start the dive. Keep in mind that the reverse is true on a hot day. When the Dive Shop is cool, your tank will increase in pressure as it warms up outside. Remember to ask for a slow cool fill next time you visit your local filling station.

Tank Temp During Fill	Tank Pressure After Fill	Tank Temp At Dive Site	Tank Pressure At Dive Site
°F	psia	°F	psia

Pressure

Pressure:
Imagine a column of air 1 inch square that starts from the atmosphere and continues all the way down to sea level. The weight of this column of air is equal to 14.7psi (Pounds Per Square Inch). This is also known as 1 ATM (Atmosphere). As we travel down the water column, the weight of every 33ft of Sea Water or 34ft of Fresh Water is equivalent to another ATM of pressure. With this in mind, we have 1 ATM atmospheric applied to us before we enter the water at sea level. At 33ft of sea water, we have 2 ATM (1 atmospheric and 1 hydrostatic). At 66ft we add another and so on. Below is a calculator that converts depth in feet to ATA (The sum of atmospheric pressure plus hydrostatic pressure is called absolute pressure expressed as ATA) and PSI. Try it for both Sea and Fresh water.

Nitrox MOD (Maximum Operating Depth)

Nitrox MOD:
Nitrox or Enriched Air Nitrox has many advantages over compressed air. For example, with Nitrox you have less chance of Nitrogen Narcosis, shorter SIT (surface interval time), and the lower amount of nitrogen in your system decreases the risk of Decompression Illness. It also has some disadvantages over compressed air. One of the few disadvantages is, as the Partial Pressure of Oxygen increases (due to depth) so does your vulnerability to Oxygen Toxicity. To account for this NOAA has published a table that displays exposure limits to common diving partial pressures of Oxygen.

PO2 Exposure (Atmospheres)	Maximum Single Exposure (Minutes)

1.6	45
1.5	120
1.4	150

Use the calculator below to check the MOD (Maximum Operating Depth) given a specific Nitrox mix. The most common Nitrox mixes are 32% and 36%. The most common PO2 level used for training and certification purposes is 1.4. Keep in mind that compressed air is basically 21% (20.9%) Oxygen so you can calculate your MOD with compressed air also.

PO2 - (Partial Pressure of Oxygen)	FO2 - (Fraction of Oxygen in the mixed gas designated as a percentage)	MOD - (Maximum Operating Depth)

Extend Studio