DECOMPRESSION THEORY

 

HISTORY : J.S. HALDEAN discover it in the 1900s

 

 

Henry’s law is applied to this theory (gas absorption)

 

Theoretical tissues :  tissue of the body (bones, blood, liver, heart, fat, lungs, etc…)

 

Half-live / half time : the time that a tissue absorb N2 until it’s half full

 

M-value : maximum amount of N2 in one tissue

 

 

Haldean works with 5 theoretical tissues and the biggest tissue is 75’

US. Navy table (SSI) with 7 theoretical tissues and the biggest tissue is 120’

Padi Tables with 14 theoretical tissues and the biggest tissue is 60’

 

The US Navy table have been tune-up with Doppler machine to count the silent bubbles in the body after a dive

 

The Doppler limit (or NDL) is the maximum time that we can stay underwater until the inside PPN2 equal the outside PPN2

 

Exemple:

 

            Meters             pressure in bar            percentage                  partial pressure

 

                                                                        21%02                                     0.21ppo2

            0                                  1                      +79&N2                                  +0.79ppn2

                                                                        ---------                                                ------------

                                                                        100%                                       1 bar

 

                                                                        21%o2                                     0.42ppo2

            10                                2                      79%n2                                     1.58ppn2

                                                                        ---------                                                ------------

                                                                        100%                                       2 bar

 

The NDL at 10m is 160 minutes , so after this amount of time, the body is saturated with N2 and we need to ascent otherwise we pass in decompression dive

 

 

DIVE COMPUTERS:

 

Dive computers gives more time underwater because they recalculate the NDL all the time

But on the 1^st dive, dive computer and dive table give the same amount for a given depth.

 

The same roles apply to dive computers and tables:

 

1. never share a computer
2. never plan to the NDL time
3. ascent max 9m/ minute
4. if computer fail during a dive, ascent to 5m and stay there as long as your air supply permit and don’t dive for 24hours
5. safety stop at 5m for min 3 minutes
6. always begin with the deepest dive and work shallower
7. don’t do up down up down dives
8. adjust if you dive in altitude (more that 300m)
9. wait 18-24 hours after a dive to ascent in altitude (more than 300m) or before taking a pressurized plane
10. 24 hours if taking non pressurized plane or ascending higher than 2’400m altitude

 

Computers allow multilevel diving.

 

ALTITUDE DIVING

 

1. Diving in altitude (more than 300m ) required special procedures since the atmospheric pressure is less than at the sea level and we dive in fresh water
2. when diving in altitude, you need to know your altitude to convert the real depth to theoretical depth, the capillary gauge do it automatically
3. at 5.500m the atmospheric pressure is ½ so 0.5 bar