What Ppo do Saturation divers live at in the bell?
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Bombay High
Contributor
0.8 is high. It is more in the range of 0.3 PPO2. Very exceptional circumstances might prompt higher PPO2 but generally in the area of 0.3 is about right.
Bombay High
Contributor
There are different phases of a saturation dive, PPO2 levels vary during this time. Generally speaking, partial pressures of 0.2 to 0.5 are used, but the most common is 0.4 ATA. This gives a safety margin between risks of hypoxia and pulmonary oxygen toxicity. Oxygen pressure is increased to 0.5 ATA during decompression. Because of the fire risk associated with high O2 concentrations, the chamber oxygen is generally kept below 21% during the last 10M of ascent. The alternative is to use periods of breathing high-oxygen mixtures (from a mask with an overboard dump system).
PPCO2 is kept below a limit of 0.005 equivalent to 0.5 per cent at 1 ATA. For shorter periods a higher limit, 0.015-0.02 ATA is tolerable. A high carbon dioxide level will lead to hypecapnia and a reduced work capacity. When considering carbon dioxide levels, humidity can be a problem. When using soda lime to remove the CO2, a relative humidity (RH) of over 75 per cent gives better performance. Other absorbents may require different optimal percentages. A higher RH reduces the risk of static sparks (a source of ignition in the fire risk zone). The problem with accepting a high RH is the increased risk from certain bacterial and fungal infections, which can be a problem during Sat, so the range chosen is a compromise. With water from wet gear and showering, it's often difficult to keep humidity down to the 60-75 per cent RH range recommended.
As far as diluents are concerned, helium, hydrogen and nitrogen mixtures with oxygen have been used (although other gases have been tried). The French in-particular have experimented with Hydrogen. If used in the DDC atmosphere, hydrogen must be removed during ascent so that there is none left when the oxygen concentration is high enough for there to be a risk of combustion (this is the fire risk zone; where the oxygen pressure must be kept below 0.4 ATA or there will be a fire hazard in the chamber at depths shallower than 50 M). Below this depth the oxygen is diluted with so much inert gas that a hydrogen fire just isn't a risk.
Additional nitrogen (Trimix) is sometimes used to reduce high-pressure neurological syndrome (HPNS), but as this increases the decompression profile (a decompression model that's slower than the standard oxygen/helium schedule must be used), it's another factor for the diving contractor has to consider.
The Commercial Diving Industry changes slowly. The industry has a good safety record with Heliox and for this reason it's use is most common. Helium reclaim (Divex Ultrajewel 601 Helium Reclaim Helmet) reduces the high costs of this gas (over 90% of the Helium is reclaimed).
When breathing Helium, optimal working temperature (thermal comfort) can always be problematic. Temperatures may increase between 25°C and 33°C. Any deviation may cause hypothermia/hyperthermia. This can occur rapidly and can easily be missed at the early stage.
As you can see, saturation is an expensive complex operation. There is absolutely no room for error. Saturation Divers, Supervisors and support staff need to be well trained and a solid dive plan must be made and followed.
PPCO2 is kept below a limit of 0.005 equivalent to 0.5 per cent at 1 ATA. For shorter periods a higher limit, 0.015-0.02 ATA is tolerable. A high carbon dioxide level will lead to hypecapnia and a reduced work capacity. When considering carbon dioxide levels, humidity can be a problem. When using soda lime to remove the CO2, a relative humidity (RH) of over 75 per cent gives better performance. Other absorbents may require different optimal percentages. A higher RH reduces the risk of static sparks (a source of ignition in the fire risk zone). The problem with accepting a high RH is the increased risk from certain bacterial and fungal infections, which can be a problem during Sat, so the range chosen is a compromise. With water from wet gear and showering, it's often difficult to keep humidity down to the 60-75 per cent RH range recommended.
As far as diluents are concerned, helium, hydrogen and nitrogen mixtures with oxygen have been used (although other gases have been tried). The French in-particular have experimented with Hydrogen. If used in the DDC atmosphere, hydrogen must be removed during ascent so that there is none left when the oxygen concentration is high enough for there to be a risk of combustion (this is the fire risk zone; where the oxygen pressure must be kept below 0.4 ATA or there will be a fire hazard in the chamber at depths shallower than 50 M). Below this depth the oxygen is diluted with so much inert gas that a hydrogen fire just isn't a risk.
Additional nitrogen (Trimix) is sometimes used to reduce high-pressure neurological syndrome (HPNS), but as this increases the decompression profile (a decompression model that's slower than the standard oxygen/helium schedule must be used), it's another factor for the diving contractor has to consider.
The Commercial Diving Industry changes slowly. The industry has a good safety record with Heliox and for this reason it's use is most common. Helium reclaim (Divex Ultrajewel 601 Helium Reclaim Helmet) reduces the high costs of this gas (over 90% of the Helium is reclaimed).
When breathing Helium, optimal working temperature (thermal comfort) can always be problematic. Temperatures may increase between 25°C and 33°C. Any deviation may cause hypothermia/hyperthermia. This can occur rapidly and can easily be missed at the early stage.
As you can see, saturation is an expensive complex operation. There is absolutely no room for error. Saturation Divers, Supervisors and support staff need to be well trained and a solid dive plan must be made and followed.
Bombay High
Contributor
Well ... you cannot get a more comprehensive answer than Wayne has just given you 
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