Re: [UKHAS] Gas Cylinder Safety considerations

[David Akerman]

Helium: Don't drop the cylinder on your foot

Hydrogen: http://ukhas.org.uk/guides:hydrogen?s[]=safety

On 20 March 2013 11:19, chris hillcox <ballo...@hotmail.co.uk> wrote:

I've been trying to research the topic of safety when handling and filling from a helium or hydrogen gas cylinder and wonder if anyone has any useful links general advice / 'do's and don'ts'. All comments are appreciated - even ones that may seem obvious. Thanks Chris (m6lzy)

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[gonzo_]

As it is compressed gas, rather than liquid inside the bottle, running it lying down is no problem. (most HAB fills seem to be done this way).
The cooling/ice should present no danger on the bottle. But beware of ice forming on the regulator. It could freeze up inside the regulator and affect the output pressure.

[Ed Moore]

On Wed, Mar 20, 2013 at 12:08 PM, chris hillcox <ballo...@hotmail.co.uk> wrote:

Thanks Dave. Is there any risk in having the cylinder laying on it's side as opposed to upright due to uneven ground?

Not for gases. Liquid cylinders might have dip tubes which require a specific orientation. If you don't have a stable bottle trolley or securet post to fix the bottle against, I'd always lay it on the ground.

 

Also are there any risks in emptying the cylinder all in one go?

Depends on how fast you do it...

 

When this is done the cylinder becomes cold and condensation / ice forms on the cylinder. Does this pose any risk?

I'll explain why this is happening because understanding the physical principle should also mean you can see why it's not inherently dangerous. 

This is due to adiabatic expansion. The pressure inside the cylinder is dropping because the volume is fixed but gas is flowing out. This means the average distance between gas molecules is increasing. All the gas molecules are attracted to each other via van der Walls forces, and so pulling them away from each other (due to expansion) required doing some work, i.e. it takes energy. We say this is increasing the potential energy, in a similar way to how putting a book on a higher shelf is increasing its gravitational potential energy. If you're not actively putting energy in some other way (which is what we mean by adiabatic), and the total system energy must be conserved, then this increase in potential energy must be matched by a decrease in kinetic energy, which means a decrease in temperature. So the gas cools, and so cools the walls of the cylinder that is containing it. This further reduces the internal pressure. Regulators need a certain pressure drop across them to work properly (and they ice up fastest specifically because there is a big adiabatic expansion happening within them), but the drop usually quite low, and so while you might end up not getting as much gas out of a cold bottle as a warm one, but it's not a huge difference in the grand scheme of things.

However, practical considerations: moisture in the air can ice up. Not a big problem on the cylinder but it can freeze on fittings and jam them up. Regulators are simple mechanical feedback systems - a very large temp drop can affect their performance, and possibly even their mechanical safety (though this is a bit extreme). So if they are starting to ice up badly, maybe stop the gas flow for a bit so they can warm back up.

Ed

Thanks

[Steve Aerospace]

Here is the legal side of gas carriage:- http://www.bcga.co.uk/preview/publications/L12005.pdf   The way I read it you would need to carry a few cylinders of gas to fall into the regulated area.  I'm not sure at what point is a legal requirement to carry a hazard diamond - I just carry one anyway.    

Good advice is to keep a gap open in the top of the vehicle (for lighter than air gasses) if you are holding the cylinders in there for any length of time - just in case there is a small leak and buildup of gas. Obviously check and correct any leaks. 

I always use my Helium/Hydrogen cylinders laying down for use - so they can't be knocked over.  You are supposed to transport the bottles lashed & standing up - as in the event of an accident the valves stand less chance of being knocked off.  I was advised if you can't do that due to cylinder length then arrange the cylinder so that it is propelled away from you in the case of a serious accident. Personally I think with hydrogen in this situation you be better putting your head between your legs - so you can kiss your ass goodbye ;-).

 The only problem with fast dump of gas I've noticed is that quick connects have a habit of leaking slightly or not mating properly when cold.

Steve

Steve Randall

Random Engineering Ltd

st...@randomaerospace.com

+44 7802 242135

[Adrian Hicks]

Just get a magnetic one

chris hillcox <ballo...@hotmail.co.uk> wrote:

Thanks to everyone who has commented. After Steve's comments I think I'll get one of the car signs on a suction cup.