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The vapour pressure of CO2 at 20C is ~750 psi. I don't think many airlines will match that. I would suspect the cylinder was oversize, either through fitting the wrong one or residual gas in the bladder.
Check your lifejackets at home? Here's something to think about
- Thread starter laika
- Start date
Hydrozoan
Well-Known Member
I'm sorry but I don't understand what you're saying here. Are you suggesting that jacket pressure reaches 750 psi? That’s 51 atm!
Take a look at http://www.ybw.com/forums/showthread.php?312911-66g-lifejacket-cylinder-what-volume
Or am I misinterpreting?
Strikeliner
Well-Known Member
Just a bit of info for consideration
Twin chamber SOLAS/MED Lifejackets have pressure relief valves because on auto inflation BOTH operating heads fire and both chambers receive CO2.
Single chamber leisure jackets DONT have prv's. Jackets will take their "form" or shape at around 100Mbar. Jackets are tested by approved service stations at the level specified by the manufacturer. Usually around 150 to 200 Mbar.
ISO specifications dictate that a jacket should be able to withstand 1Bar of pressure. You could easily fire two 33g/38g cylinders into an ISO jacket without it bursting. The jacket belonging to the OP was stated to be about 5 or 6 years old. This pre dates ISO 12402 an would have been covered by EN 396. (very similar)
A man in a chandlery lifeboat crew or not probably wont have known this and may have used a high pressure line and blown the jacket to bits, who knows?
This is why jackets should be professionally serviced.
Jacket seams have not been glued for years and so glue breakdown was not the cause. Most well known brand jackets have bladders lined with PU so you can blow in to them by mouth as often as you want. They wont be damaged but the may become grubby.
If the OP's jackets were cheap Chinese imports then non of the above applies and the rest should be thrown on the bonfire.
Twin chamber SOLAS/MED Lifejackets have pressure relief valves because on auto inflation BOTH operating heads fire and both chambers receive CO2.
Single chamber leisure jackets DONT have prv's. Jackets will take their "form" or shape at around 100Mbar. Jackets are tested by approved service stations at the level specified by the manufacturer. Usually around 150 to 200 Mbar.
ISO specifications dictate that a jacket should be able to withstand 1Bar of pressure. You could easily fire two 33g/38g cylinders into an ISO jacket without it bursting. The jacket belonging to the OP was stated to be about 5 or 6 years old. This pre dates ISO 12402 an would have been covered by EN 396. (very similar)
A man in a chandlery lifeboat crew or not probably wont have known this and may have used a high pressure line and blown the jacket to bits, who knows?
This is why jackets should be professionally serviced.
Jacket seams have not been glued for years and so glue breakdown was not the cause. Most well known brand jackets have bladders lined with PU so you can blow in to them by mouth as often as you want. They wont be damaged but the may become grubby.
If the OP's jackets were cheap Chinese imports then non of the above applies and the rest should be thrown on the bonfire.
LadyInBed
Well-Known Member
Yes, misinterpreting.
The CO2 might be at high pressure in its cylinder, but when it escapes into the jacket its volume will increase so the pressure will decrease.
Hydrozoan
Well-Known Member
Yes I do understand the physics of gas expansion. But Quiddle said he would suspect that the cylinder was oversize. I thought the inflation was by compressor, adjusted in some unspecified way so as to give normal inflated pressure in the jacket ? So I don’t see where the VP of CO2 or a larger cylinder comes into it.
But my apologies in advance to you and Quiddle if I am being more than usually daft …
LadyInBed
Well-Known Member
My apologies.Yes, I'm with you on that, cylinder not relevant.
Daydream believer
Well-Known Member
I am sure you are perfectly correct, but I only understand "bars" when there is a young lady with a set of beer pumps behind them.
From my school days 1Bar was 1 atmosphere which was 14 PSI- is that correct?
Therefore 2Mbar is 2.8PSI. Is that right?
So for comparison with something I understand -The instructions for my Avon dinghy ( long since lost) said max pressure was 3 PSI- basically stop pumping when I get knackered
So my life jacket should be Ok inflated to half an Avon-- ( 1.5PSI) Is that what we are talking about?
because if it is , for a life jacket to go "pop" at that it must have been well rotten or well over inflated
If i had to manually inflate in the event of cylinder failure or because I had to deflate to get out of an upturned boat I would never get anything like that into it to keep myself afloat.
Possibly a couple of puffs for .5PSI tops, by which time I would be dead from oxygen starvation long before I drowned
I am beginning to wonder if I might be better off with my dinghy buoyancy aid with a separate harness
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Strikeliner
Well-Known Member
Your recollection and knowledge of Physics is far superior to mine. I believe however that your figures are correct.
200 Mbar is as near 3 Psi as make little difference. I have no idea about Avon dinghy pressures but I suspect that your figure is correct.
Your point that the jacket must have been well over inflated or well rotten is pretty accurate I would say. That's the reason that people who are unsure should have their jackets serviced properly. The cost is only about £10.00 +/- pr jacket.
I should repeat that the jacket will take it's shape at around 100 Mbar maybe a little less and will perform correctly at that level. The 200 Millibar figure that I have mentioned is the "extra" pressure used to complete an air holding test when servicing.
You could inflate the jacket orally to that level 70 - 100 (Mbar) but granted you would be tired. The oral tube itself is as you will know there to allow this to be done, not necessarily from deflated but to top up where necessary.
IMHO you would be much better served using an inflatable jacket than a buoyancy aid but each individual is free to make their own choice.
200 Mbar is as near 3 Psi as make little difference. I have no idea about Avon dinghy pressures but I suspect that your figure is correct.
Your point that the jacket must have been well over inflated or well rotten is pretty accurate I would say. That's the reason that people who are unsure should have their jackets serviced properly. The cost is only about £10.00 +/- pr jacket.
I should repeat that the jacket will take it's shape at around 100 Mbar maybe a little less and will perform correctly at that level. The 200 Millibar figure that I have mentioned is the "extra" pressure used to complete an air holding test when servicing.
You could inflate the jacket orally to that level 70 - 100 (Mbar) but granted you would be tired. The oral tube itself is as you will know there to allow this to be done, not necessarily from deflated but to top up where necessary.
IMHO you would be much better served using an inflatable jacket than a buoyancy aid but each individual is free to make their own choice.
mjcoon
Well-Known Member
I don't know where these capital Ms are coming from; they would be megabar. Millibar would be mb and a thousandth. So 200mb would be your 2.8 psi (one fifth atmosphere).
I suppose the bladder has to be inflated enough to withstand shallow immersion. Its buoyancy will decrease if taken deep.
Mike.
Hydrozoan
Well-Known Member
No problem - I was a bit puzzled, but am very capable of getting the wrong end of a stick!
laika
Well-Known Member
These only have "Use with 33gms CO2 Cylinder". They did/do have 33g cylinders. I've emailed mullion to try and ascertain age/pressure from a serial number (no model number printed on any label).
The label on the lifejackets says EN396/1993. They're made by mullion. The "manufactured by" company address is in scunthorpe, which of course doesn't necessarily mean that that's where they're made.
That's how much I paid. I have retrospectively looked for mullion-approved service stations and the closest one is at least 3 hours away by train, bus and walking. I'll repeat that the guy I spoke to (a) said that what happened was extremely rare (this was only the second time he'd seen it happen) and (b) seemed to know what he was talking about . You may discount this as I am clearly no lifejacket expert but I do have pretty sensitive BS detectors
mjcoon
Well-Known Member
Ah, 33g of liquid CO2 will give 33g of gas. So it should be possible to work out its volume at room/sea temperature and any pressure. Then you just need to know the volume of the jacket bladder...
Mike.
Daydream believer
Well-Known Member
Are you sure it is CO2. Imagine someone topping up the inflation tubes by mouth & accidentally getting a mouthful of CO2. Or come to that actually deflating the jackets in a confined space after use
Would not help much would it. I know that there are non return valves but in the event of problems CO2 cannot be the most user friendly.
Hydrozoan
Well-Known Member
33 g will give a volume of ca. 16.8 litres at standard temperature and pressure (STP is 0 deg C and I atmosphere).
I could not find LJ chamber volumes in a quick search, but if a 150 N jacket has a chamber volume of about 15 litres (? - displaces 15 litres of water, equivalent to ca. 150 N) that gives an (over)pressure of just 0.12 atm (1.8 psi) at 0 deg C.
That increases with temperature to about 0.17 atm (2.5 psi) at 15 deg C and about 0.22 atm (3.2 psi) at 25 deg C.
For comparison, the pressure at which the child’s balloon here reaches near its full volume (long before it bursts) is about 120-130 mmHg, which is about 2.3-2.5 psi. https://www.youtube.com/watch?v=fwh-i0WB_bQ
But I hope somebody will check my assumptions and calculations – they are not guaranteed!
Edit: And strikeliner's 150-200 millibar test pressure is about 2.2-2.9 psi, BTW.
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Strikeliner
Well-Known Member
Laika you have a pm.
bitbaltic
Well-Known Member
I can hardly imagine cylinders of compressed oxygen being a top plan for life jacket inflation, and as every other gas is effectively as poisonous as CO2 just by dint of not being oxygen, I think you will be stuck with it. It's not CO
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mjcoon
Well-Known Member
Quite. The point about CO2 is that is liquefies, thus limiting the pressure as you pump more into the cylinder (as given by the vapour pressure as already specified). This gets round the simple perfect gas Boyle's Law (IIRC!) limitation.
The amount of CO2 in a fire extinguisher is much more likely to be problematic than the few litres in an inflation cylinder.
Mike.
anoccasionalyachtsman
Well-Known Member
Quite hard to orally inflate a lifejacket without putting a lot of CO2 in it either.
prv
Well-Known Member
Well, not a huge amount. From memory the "standard" figures for exhaled air are 80% nitrogen, 16% oxygen, and 4% carbon dioxide.
If people breathed out pure CO2 there wouldn't be much point in mouth-to-mouth
Pete
Daydream believer
Well-Known Member
If people breathed out pure CO2 there wouldn't be much point in mouth-to-mouth
Pete
If they did the EU could leave car emissions alone & just ban breathing