Accidents

[Dr Deco]

Hello Mike F:

I understand what you mean. I was referring to those few minutes of missed decompression. A situation such as this resulted in the tragedy a couple of years ago in California. The diver hastily gather some equipment and reentered the water alone for a few minutes of missed decompression. The haste lead to some problem, and she drowned.

Dr Deco :doctor:

 

[adder70]

Hello Scuba Board Readers:

Deck Decompression

Military and commercial divers seldom will decompress in the water if there is a long decompression and another option available. For decades, it has been standard practice to decompress in a bell that was placed at the depth of the first Haldane stop.

Another option is to perform surface decompression by extending the forty-foot stop, on oxygen, and then coming directly to the surface. The diver then doffs is diving equipment, and within five minutes enters a deck decompression chamber (DDC) and is taken back down to forty feet of pressure. The diver will then complete the decompression in the DDC. The divers are told to keep activity to a minimum while on the surface.



Dr Deco :doctor:

I had heard some time ago that saturation divers at deep depths (~400ft) would actually ascend to a bell at a lesser but still fairly deep (~200ft) and the bell would be removed and put on deck. This would then serve as a DDC, where the divers would remain compressed at about 100ft for a few days (working a couple hours at 400ft each day) and then spend a week or two in an "ascent" to surface pressure. Is this actually done or was it ever done?

 

[Dr Deco]

Hello Corry:

Saturation Diving

This is how saturation diving is actually performed. The divers do not stay saturated at the working depth in the water. They will enter a bell that is then taken, under pressure, to the surface. The divers generally will have a habitat pressure that is less than the working depth. They can perform a dive downwards and return to some intermediate pressure. [This is not any different than thinking of sea level as an intermediate pressure between depth and the reduced pressures of very high altitude.

For the decompression, a rule of thumb for ascent from saturation is 100 fsw per day.

Dr Deco :doctor:

 

[Goeduck]

I have a question along the same lines. Please forgive me if someone views this as an attempt to hijack this thread. It certainly is not my intent.

If a diver comes to the surface with definite indications of DCS, help is usually called for immediately. It seems to me that in most cases, what happens next is, the medevac chopper comes thumping onto the scene to carry the injured diver to the closest decomp chamber, at altitude . To be sure, the injured diver is more then likely being administered O2 by the rescue personnel, but it is still at altitude.

I always thought (there I go, thinking again) that is was best to keep the diver closer to water level. Doesn't the flying at altitude exacerbate the problem that the diver has, that is, DCS?

I realize that the chopper is probably the fastest way to get the diver to the chamber, but I have wondered about that for quite some time.

 

[letoktok]

i would have to say, not beeing a doc or anything, i think the helicopter actually stays really low. Because the air pressure is not as strong as water pressure you can actually go high i guess. I mean at 30f in wate the pressure is 2atm, at 30f in air it's not 0atm, half of what it would be at sea level.
I don't have the numbers but i think as long as he stays under 1000f (300m) the pressure change is minimal. Then again i am probably talking out of my a**. But appart for the numbers i think it's somehting to that regard.
Anybody can correct me (not a sensitive wrong person))

 

[fins wake]

I always thought (there I go, thinking again) that is was best to keep the diver closer to water level. Doesn't the flying at altitude exacerbate the problem that the diver has, that is, DCS?

Yes indeed! This is the reason that medevac choppers fly suspected DCI victims at very low altitude to the nearest chamber if they can. U.S. medevac choppers will (or should) know this, but in some countries the chopper pilots may not share this knowledge. It is therefore a good idea to verify/remind/explain to the chopper pilots that they should try to fly as low as possible, and preferably under 300 metres (1000 feet) when transporting the victim, as most helicopters don't raise the cabin pressure. Of course, sometimes weather conditions etc may cause other hazards.

In a similar manner, aircraft with pressure cabins should try to hold the cabin pressure as high as possible (giving a low 'altitude'). Most commercial airlines can do this to a degree if the captain understands the issue (go through DAN).