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View Full Version : Airline use (land use) - any DCI risk at depth?



Treerat
31-07-2014, 08:02 PM
An odd question that I probably should know the answer to but.......

On a course last week we were looking at sewer and combined space rescues. For the practical exercises were were lowered 10m underground, carried out search and rescue then retrieved the casualty to the surface.

Although we usually work fairly shallow our kit allows us to drop a maximum of 50m with a working duration (9l cylinder) of 47 minutes. However we are looking at extending this with a surface supply.

Is there a risk of DCI working below ground but out of water? I seem to remember that there were a number of deaths when the London sewers were built that they put down to the bends? Is there a profile that can be followed as per our scuba ones to help reduce any risks?

I asked the question on the course but was told that the risk didn't exist, however this doesn't seem to fit with what I can remember.

Ta

BenL
31-07-2014, 08:09 PM
At ground level, the pressure difference is approx 1mBar/10m. For an open shaft, I expect this to remain so. Otherwise all those miners would get bent at the end of every shift.

Treerat
31-07-2014, 08:17 PM
At ground level, the pressure difference is approx 1mBar/10m. For an open shaft, I expect this to remain so. Otherwise all those miners would get bent at the end of every shift.

They are breathing air forced down from the surface which pressurizes the mine rather then self contained air?

BenL
31-07-2014, 08:33 PM
They are breathing air forced down from the surface which pressurizes the mine rather then self contained air?

Sometimes, yes. But then due care in those cases is made. But in your case, it's all millibars, surely? With a surface supply using a demand valve, then should be no problem? An instructor friend of mine uses Felix Baumgartner's record skydive to illustrate: he fell from 40km and covered approx 1000 milliBar. Descend 30m in the water and you've covered 4000 millibars.

gobfish1
31-07-2014, 08:49 PM
An odd question that I probably should know the answer to but.......

On a course last week we were looking at sewer and combined space rescues. For the practical exercises were were lowered 10m underground, carried out search and rescue then retrieved the casualty to the surface.

Although we usually work fairly shallow our kit allows us to drop a maximum of 50m with a working duration (9l cylinder) of 47 minutes. However we are looking at extending this with a surface supply.

Is there a risk of DCI working below ground but out of water? I seem to remember that there were a number of deaths when the London sewers were built that they put down to the bends? Is there a profile that can be followed as per our scuba ones to help reduce any risks?

I asked the question on the course but was told that the risk didn't exist, however this doesn't seem to fit with what I can remember.

Ta

some of the digging will have hit water , they used to pump in air to keep the water at bay , so the workers would be under Pressure , ie caisson worker',s

had tables be4 divers that s were are tables started ,

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCIQFjAA&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHistory _of_decompression_research_and_development&ei=8q7aU-KTG63o7AaU64GABQ&usg=AFQjCNH3G0ljIxh3o_DC0mcGEajD6FHBVw&bvm=bv.72185853,d.ZGU&cad=rja

notdeadyet
31-07-2014, 09:08 PM
Yeah, tunnels would have been pressurised with air locks at the entrances while they were digging them. Same for bridge footings in big rivers like the Hudson in New York, they'd build a wooden dome on the river bed called caissons, blow it with air and the workers could construct the foundations in the dry. Workers used to suffer caisson disease, it got known as the bends because a dance called the Grecian Bend was in fashion at the time.

Unpressurised you'd have to go to a hell of a depth underground to risk a bend.

gobfish1
31-07-2014, 09:15 PM
Yeah, tunnels would have been pressurised with air locks at the entrances while they were digging them. Same for bridge footings in big rivers like the Hudson in New York, they'd build a wooden dome on the river bed called caissons, blow it with air and the workers could construct the foundations in the dry. Workers used to suffer caisson disease, it got known as the bends because a dance called the Grecian Bend was in fashion at the time.

Unpressurised you'd have to go to a hell of a depth underground to risk a bend.

over 100 bent doing the footings on one new york bridge ,

think thats also were the deco beer came from ,

Tim Digger
01-08-2014, 06:01 AM
The very deep high altitude mines like those in the Andes (remember the trapped miners a few years ago) are supplied with pressurised air for ventilation, the combined increase in pressure in the confined space caused by the emergency air supply without obvious provision for exit of gas, and the extreme difference between exit altitude and working depth required them, when rescued to be decompressed slowly.
Otherwise unless there is some similar reason why there is a significant pressure differential (>50kpa , half a bar, 380mmHg) between working place and surface then no problem. Caisson working on river footings is pressurised to keep out the water and is the original described cause of DCI (St Louis Mississippi bridge mid 19th C).

Mark Chase
01-08-2014, 06:24 AM
An odd question that I probably should know the answer to but.......

On a course last week we were looking at sewer and combined space rescues. For the practical exercises were were lowered 10m underground, carried out search and rescue then retrieved the casualty to the surface.

Although we usually work fairly shallow our kit allows us to drop a maximum of 50m with a working duration (9l cylinder) of 47 minutes. However we are looking at extending this with a surface supply.

Is there a risk of DCI working below ground but out of water? I seem to remember that there were a number of deaths when the London sewers were built that they put down to the bends? Is there a profile that can be followed as per our scuba ones to help reduce any risks?

I asked the question on the course but was told that the risk didn't exist, however this doesn't seem to fit with what I can remember.

Ta


As above ask them the diferance with the caisson workers?

I can only asume its the breif time your down with makes the exposure negligable. Those guys were probably don 12 hours or something daft.

ATB

Mark

Steve Clark
01-08-2014, 07:35 AM
Traditionally, caissons were sunk under pressure to prevent water filling the excavation. Men worked inside these and everything came in and out through an airlock. 'Dives' such as 15-20m for 8hours, then instant decompression! Lots of people injured and killed. Brooklyn bridge in NY was one of the first major examples.

Occasionally, this technique is still used today. One of the shafts on the Jubilee line extension was converted into a sealed pressurized caisson when they were inundated from an aquifer. Modern techniques such as cased piling and diaphragm walling, pressurized using bentonite and tunneling with earth pressure balance tunneling machines have made working in compressed air less common. (Although fitters still need to maintain the tunneling head by passing through an airlock)

If you are working at atmospheric pressure (i.e. in a sewer), there are no deco issues. You just need enough air to get out if the atmosphere is un-breathable.

Steve

gobfish1
01-08-2014, 10:03 AM
iv a few Badgers for working in Confined Spaces, long time back , out of date now ,


hydrogen sulfide, ammonia, carbon dioxide, methane, nitrogen, and hydrogen . were the things i remember , as the mane problems and flooding ,

Nickpicks
19-08-2014, 11:58 AM
Unless you have a pressurised tunnel / caisson which you have to enter through an airlock, then the pressure you're exposed to will be atmospheric plus the extra weight of air. The pressure change would be about 5 millibars, so there's no need to worry about it causing any DCI problems.

If it was a problem, then anyone ascending a tall building like the Burj Kalifa would need decompression stops on the way up in the lift.

If it's what you're using for vertical entry confined spaces / sewers, then they'll all be open to atmosphere, so virtually no pressure effect.


If you were using the same BA in a pressurised caisson, you'd have to reduce the working time in the same way as you'd calculate gas requirement for a dive.


That's a point: If you were living in the Burj Kalifa, you'd have to allow a desat time or use transfer tables in order to go home afterwards!

Tim Digger
19-08-2014, 04:29 PM
That's a point: If you were living in the Burj Kalifa, you'd have to allow a desat time or use transfer tables in order to go home afterwards!

Exactly the problem with the Andean Miners rescue a few years back.

greatwhite
12-10-2014, 07:40 AM
But weren't mine workers in the olden days getting bent after a long shift underground?

matt
12-10-2014, 09:10 AM
Caisson disease came about due to pneumatic caissons - basically tubes stuck into mud and pressurised to keep the water out. When the worker came out of the pressurised tube they developed the bends as they had been in a pressurised environment. Popping down an open-air drain isn't going to give you the bends.

Matt.

John_ZA
10-01-2015, 07:14 AM
But weren't mine workers in the olden days getting bent after a long shift underground?

In SA we have mines going almost 4000m, these are not pressurised and as far as I am aware no miners ever get bent or we'd have the unions calling for strike action. They do have aircon though.