Metre sea water
The metre (or meter) sea water (msw) is a metric unit of pressure used in underwater diving. It is defined as one tenth of a bar.
| metre sea water | |
|---|---|
Hyperbaric chamber pressure gauge calibrated in msw and bar | |
| General information | |
| Unit of | pressure |
| Symbol | msw |
| Conversions | |
| 1 msw in ... | ... is equal to ... |
| SI units | = 10000.0 Pa |
| CGS units | = 100000 Ba |
| U.S. customary | ≈ 3.263 fsw ≈ 1.45038 psi |
| foot sea water | |
|---|---|
Pressure gauge on Siebe Gorman manual diver's pump calibrated in fsw and psi | |
| General information | |
| Unit of | pressure |
| Symbol | fsw |
| Conversions | |
| 1 fsw in ... | ... is equal to ... |
| SI units | ≈ 3064.3 Pa |
| CGS units | ≈ 30643 Ba |
| U.S. customary | ≈ 0.44444 psi |
The unit used in the US is the foot sea water (fsw), based on standard gravity and a sea-water density of 64 lb/ft3. According to the US Navy Diving Manual, one fsw equals 0.30643 msw, 0.030643 bar, or 0.44444 psi, though elsewhere it states that 33 fsw is 14.7 psi (one atmosphere), which gives one fsw equal to about 0.445 psi.
The msw and fsw are the conventional units for measurement of diver pressure exposure used in decompression tables and the unit of calibration for pneumofathometers and hyperbaric chamber pressure gauges.
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