CO2 Extinguisher Diptube faults

[gm137]

I recently conducted the required 10-year discharge test for a number of CO2 extinguishers at a local components firm, combining it with "live fire" training for the staff. On actuating one unit, the discharge was particularly noisy and produced little condensed water vapor - similar to the last few seconds of a normal discharge when only gaseous CO2 is emerging.

The staff on hand to recharge the units removed the valve assembly from the unit, to find that the internal diptube was not connected to the assembly, and that the consequent discharge of gaseous, rather than liquid CO2 had solidified a good 2/3 of the charge in the extinguisher body. The diptube and valve were in good condition, and the tube could be screwed securely on to the valve

Just wondered if anyone else has had experience of such failures, or with procedures for detecting them? The unit was purchased new in 1997 from Chubb, and recieved an annual service / monthly visual inspection for the ten years it remained in service.

Thanks.

[John Dragon]

If a dip tube has come loose, you can usually hear it rattling around.

What on earth were they doing removing the head of a co2 cylinder with contents inside it?
How did they know that it was not the valve that had failed and there was still pressure inside?
Worrying.

[gm137]

Yes, I was slightly concerned re. hammering off the head of a steel missile with 56 Bar pressure inside it, but I was assured "we know what we're doing" - so I adopted for prudent cowardice and stood behind something very solid. Given the amount of dry ice still in there, a few more minutes for it to sublime and we could have had quite an eventful day.

Thanks for the advice re. the diptube: I didn't check before discharge, and afterwards, it would have been lodged in place by the dry ice forming. We've had all the usual problems with CO2 units over the years (gland on the joint to the horn loose& venting CO2 on to the operator's hand, loose horn nut that gives the unit a nice case of Brewer's droop), but I'd never come across a loose diptube. Have written to Chubb, and am awaiting their comments with interest.

[Psuedonym]

If a dip tube has come loose, you can usually hear it rattling around.

What on earth were they doing removing the head of a co2 cylinder with contents inside it?
How did they know that it was not the valve that had failed and there was still pressure inside?
Worrying.

Quite right John!

Also: Who were the staff on site to recharge the units i.e. trained, experienced in Co2 refilling etc? Did they have a Co2 pump and cylinder (One ton I think) with them? Wouldn't the continual smashing of the valve have loosened the diptubes?

As you say, worrying.

[gm137]

Yup. As I said, none of our chaps were too impressed either. The company doing the recharging were hired by the firm who brought us in to do the training, and used BOC-Style units (a cross between large cylinders and cryogenic dewars), combined with some brute-force-and-ignorance to achieve their objective. I hasten to add that, if we're asked to refill extinguishers for a client, we transport them to a specialst industrial gases firm in Nottingham, and we recommended the same to this particular customer. I don't condone (indeed, I heartily condem) the idiocy of the recharging firm: it just happens that they highlighted a (for me) unusual failure - thanks for your comments re. the rattling diptube, which I'll bear in mind in future annual inspections.

I think you're probably right about the dip-tube displacement during removal. There was definitely some problem with the discharge (from the visual evidence of the discharge pattern and the solidifying of the charge evident on opening), but the indelicate removal probably exacerbated this to the point where it's not clear exactly what happened.

Anyway, thanks again for your input.

[AnthonyB]

Late to this but must agree the field stripping of a pressure vessel in this way would not go down well with the HSE & is asking for someone's head to be knocked off - one of the small number of extinguisher deaths that has occurred since 2000 was down to a CO2 and this was a simple case of uncontrolled venting by being knocked over onto it's valve with no discharge horn attached - it's shot off like a rocket & killed a person, whereas going  one further by de-valving is worse still.

I must say it's very unusual for genuine Chubb manufactured stuff to be duff, but it's not impossible - sounds like a loose dip-tube though - must have been a duff batch.

Did Chubb service them since new or have other companies serviced them since - other than your statutory rights the 10 year warranties that Chubb & Nu Swift have offered in the past are voided if they don't do the servicing.

Fillers sound like cowboys- why were they on site to refill them when they would be breaking the law as the cylinders require their statutory 10 year retest?

Sound like they are using the 'emergency decant' method, a last resort method when a transfer pump isn't on hand - you connect the donor to the recipient, transfer a few pounds of CO2 to the recipient, then rapidly vent it to ice & cool it so it will accept the full charge.

My blood boils when I come across the many disreputable individual traders and larger firms that are out there!

[kurnal]

Interesting thread. I always thought that cylinders had to be sent to a specialist contractor to conduct the 10 year hydraulic pressure test on the cylinder  or are there companies with mobile rigs doing this now?

How many diferent types of replacement valve would they need to carry to match all the different types  they may encounter on site?

And just another thought- those small and cheap 1kg CO2 extinguishers on the market- imports from the US- do they generally have a CE mark? As there is only a 5 year period between hydraulic pressure tests in the US is it safe to use them for double this period in the UK as we set a requirement for 10 year tests?

[gm137]

Thanks for all your input. We've talked to the firm who hired our friendly local CO2 idiots, and have replaced their CO2 and stored-pressure extinguishers with hired (new) units, so that we can send off the units in question for hydrostatic testing (which we're not licensed to do ourselves). We'd been hired to carry out training to coincide with the discharge test, and it seems the firm were relying on the cowboys to not only refill, but also certify their units. "Worrying" isn't the word.

Asking around in the Notts area, some colleagues say they have come across customers using this particular recharging firm before, and have experienced problems such as under / over filling and incorrect service records. This being the case, we've contacted trading standards & the LAFB to make them aware of the situation.

Chubb have responded quickly to my contact, and are removing the loose-diptube extinguisher for inspection. Sounds like a manufacturing error from what they're saying.

The lethal nature of mistreated and / or corroded extinguishers is well-recorded; my first year in the trade coincided with the publication of Stephen Barlay's book "That thin red line", which (in a scathing attack on the cowboy maintanence / repair trade) contains details of a fatality involving a cartridge-operated dry powder unit failing in the US. Trouble is, while there are firms willing to pay for lethal cheapness, the "fly-by -night" merchants will always be there.

[AnthonyB]

Notts area? A PM about who the company is would be of use....

The only 1kg CO2s currently on the market that I know of are not from the US, but are made by Soda-Club Ltd in Israel & retailed by end suppliers under the FireKwencher brand or from Jactone (who 'own label' them).

The versions in the UK are to EN standards, all being Lloyds Register & LPCB certified with CE marking and the 2 kg model is kite marked. Having PED approval & being manufactured to the appropriate BS for aluminium cylinders they are under the 10 year regime without any additional risk.

Hydrotesting of extinguishers is a workshop only process that should only be carried out by approved competent bodies as being Category III pressure vessels only notified bodies and HSE approved third party organisations under the Pressure Equipment Regulations 1999 can legally carry this out. In theory you could fit the kit in a (very large) van, but you don't usually see it*, as for valves aluminium cylinders with parallel thread valve is almost universal now so you wouldn't need too many different ones unlike years gone by when several different types of cylinder and valve abounded.

I shouldn't be surprised - I've seen companies be unaware or ignorant of the requirement to pressure test, or not be using the correct intervals & one company that stamped the bodies, but never tested them.

* in the olden days when in the UK pressure testing of all types was routine and used as a means of assessing whether corrosion was sufficiently advanced to condemn the extinguisher field testing was more common with hand/foot pumped testers that were screwed in place of the discharge hose - in my extinguisher catalogue/literature museum I have several photos of such testing in progress outside the engineers little van.

[kurnal]

CO2 is a very unconventional chemical. It sublimes from solid to vapour at temperatures above -78C  missing out the liquid phase. Heres some more information  taken from the MSDS website:

Solid carbon dioxide (Dry Ice) is always -78 oC (-109 0F) at regular atmospheric pressure regardless of the air temperature. Handling this material for more than a second or two without proper gloves can cause serious blisters or worse. Carbon dioxide gas released from a compressed gas cylinder (such as a fire extinguisher) poses a similar danger. Avoid putting any bodily part directly in the path of discharge and be careful when touching any metal parts that the gas flows through.

Pressure Explosion. Carbon dioxide has a vapor pressure of 830 psi at 20 °C. In other words, if one places solid carbon dioxide in a closed container at room temperature, the carbon dioxide will eventually convert to liquid and the pressure above that liquid will be 830 psi (approximately 56 times normal atmospheric pressure). The pressure will always be 830 psi as long as some liquid carbon dioxide is present in the closed container, and at higher temperatures the pressure will be even greater.


Heres a couple of further questions.

Firefighters always treat gas cylinders such as LPG and acetylene with great care. Do CO2 extinguishers represent a particular hazard to firefighters if exposed to heat? The cylinder can be of aluminium, which loses its strength at much lower temperatures than steel. Obviously there is no risk of a bleve in the case of CO2.

Looking at cylinders and fire  in general the critical temperature of the liquified gas is a major consideration- especially where this temperature is fairly low such as butane and propane.  But CO2 is a different. If I were to draw a graph to show the increase of pressure with temperature in the cylinder would it be a straight line or curve?

If the cylinder contains liquid why are extinguishers not classified in terms of liquid volume- 2 litre or 5 litre rather than 2 and 5 Kg

Finally as the CO2 is in liquid form in the extinguisher how come I can never feel it sloshing about?

[John Dragon]

CO2 extinguishers have a bursting disc (pressure relief device) built into the valves. I am not aware of any such device on a CO2 cylinder (e.g. brewery cylinder).

[AnthonyB]

Presumably the weight is used as opposed to the liquid volume as it's more practical - filling as well as servicing is all based around measuring weights, which is far easier than trying to measure liquid CO2.

As mentioned CO2 extinguishers (unlike most bulk/industrial cylinders & some brew/catering valves) have a bursting disc to safely vent the contents should the pressure exceed working pressure by a significant degree (e.g. overfills or heating) - as long as it isn't painted up or otherwise rendered defective.

Why can't you here it slosh? Because it is a supercritical fluid under normal conditions, having the density properties of a fluid, but the flow characteristics of a gas, hence it won't slosh around if you shake it. If you cool a cylinder of CO2 enough, however, the liquid CO2 ceases to be supercritical and will then slosh around.

(OK I don't know the above off by heart - I read Chemistry: The Molecular Science By John W. Moore, Conrad L. Stanitski, Peter C. Jurs, which uses CO2 in extinguishers as an example of critical pressure & temperature in gases)

[kurnal]

Presumably the weight is used as opposed to the liquid volume as it's more practical - filling as well as servicing is all based around measuring weights, which is far easier than trying to measure liquid CO2.

Thats a good point!

And thanks Anthony for taking so much trouble to research the reply. I knew I could rely on you.

As for supercritical liquids I'll be happy to take your word for it. But I am still interested in that temperature / pressure relationship if anyone knows the answer!

[Tom Sutton]

The critical temperature of CO2 is 31degrees so any temperature above that it could not remain a liquid and would convert to gas, where Boyles Law would take over. Up to 31 degrees the pressure would be 830 psi then the pressure would go off scale and I would expect a big bang similar to butane cylinders which make a spectacular display not only because it’s flammable but because of the increase of pressure. I think.

Check out http://www.scienceclarified.com/Ga-He/Gases-Liquefaction-of.html

[kurnal]

Thanks TW but I think that website is wrong. They are right for many gases but not for CO2. I think they picked the wrong gas to use as an example becuse CO2 as Anthony says is a supercritical liquid.

But not many other substances can go straight from solid to vapour and miss out the liquid phase either.

The ambient temperature reaches 31 degrees on a decent summers day.