Dangers of O2

[WI_diverPaul]

OMG you guys need to see what happens if you try to build your own Hyperbaric chamber....

think I'm going to be sick.


http://www.sundaytimes.co.za/2004/02/01/news/gauteng/njhb01.asp

 

[Otter]

A tragic accident. According to the article, they had been using it for years. I guess this also emphasizes the need / reasons why hydros are important for cylinders. I wonder how one 'tests' a chamber like that.

 

[Wreckie]

They are tested by getting filled with water and pressurised to their test pressure, same as a cylinder but on a much grander scale.

It is likely that the chaimber was working on an all oxygen atmosphere as opposed to the usual method of breathing from a mask feeding you O2 while the chaimber is filled with air. This is safe(ish) however there have been a number of similar explosions when someone has taken something flamable into the chaimber, a parafin gas handwarmer is a favourite amongst suicidal geriatrics. Other implements of disaster include a child with a toy gun who incinerated himself and the nurse with him.

Mike

 

[Otter]

I was under the impression that during a hydro, a cylinder was placed in a vessle and emersed in water and then filled with water. the amount of water being displaced from the vessel was used to determine the amount of expansion. Is this incorrect? If not, you must need a pretty big vessel to emerse the chamber in UNLESS you are somehow measuring the amount of water going into the chamber to determine the amount of expansion -- I suppose that would work.

 

[FredT]

Please note that the wall thickness of the unit was reported to be between 4 and 6 inches. Given that the maximum pressure used in most hyperbaric chambers is 5 bar gauge, the wall thickness should have been more than enough. I expect Wreckie's point that something inside detonated and caused a pressure spike is a reasonable excuse. An alternative is somthing akin to SLC on Aluminum cylinders. A defect (normally near a penetration) creates a crack that grows, eventually becoming somthing that will cause the vessel to fail.

Hydro may or may not catch it, most likely not unless failure is/was immenent..

 

[diverrick]

It looks like there is a blackened/char area along the tear lines, indicating flame impingment or sooting. My SWAG would be that something was in there that was flammable, combined wot Oxygen, and you got a bomb, with people inside, in this case. Too bad, at least it was quick.

 

[ElectricZombie]

Hmmmm...I wonder where you go to buy your own hyperbaric chamber. Seems odd that they guy just had one in his back yard.

 

[iain/hsm]

In responce to this tragic event in South Africa I offer some comment.

In the newspaper report there is no report that this was a shell failure due to an oxygen fire although this is the most likley explanation. Hyperbaric fires occur when oxygen concentrations exceed 25% but only when comnbined with ignitable material and an ignition source including oil and grease.
Secondly the quote "home-made" chamber may not entirely refer to the fabrication of the shell, that frankly is beond the mechanical handling of most of us at home. The report also states that the shell was between 10 cm to 15 cm thick is mistaken.

In the UK a chamber designed for diving 1500 mm diameter and 100 MSW depth rated is only 10 mm thick even allowing for a 1 mm corrosion allowance. While to the same design calculations a medical hyperbaric chamber of 2500 mm diameter rated to 50 MSW can also be the same thickness. (calculated using certified quality boiler plate steel to BS 1501-224-490B LT50 and BS 5500 design calculations)

Not all chambers for human occupancy are hydrostatic tested even in the UK
Those that are are either "proof tested" (pressurer held for one hour) or in addition are tested for permanent "set", by measuring the amount of water needed to expand the shell under load, against the lesser amount of water returned when pressure is released. The difference is calculated as a permanent set. Testing type is up to the insurance company to decide.

Regarding the "did not have a licence for the thing" and legislation is an interesting issue, for even in the UK there are a number of chambers all of which elude a different history.

The salient fact is that this tragic event is the consequence again of pressure and oxygen mistakes.