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Dangers of A Deuterium Cylinder

Posted: Sun Jun 01, 2014 10:44 pm
by Liam David
Before I'm allowed to buy a deuterium cylinder and store it in the basement, I have to convince my dad that the risks involved are next to zero. What are the main safety concerns of storing a 25L cylinder and where should I store the bottle?
Thanks,
-Liam David

Re: Dangers of A Deuterium Cylinder

Posted: Mon Jun 02, 2014 4:26 am
by John Futter
Liam
It is about as dangerous as a butane cigarette lighter refill aerosol with regards to flammability. You know the ones that are about the size of a flyspray canister.
Second thought flyspray uses hydrocarbon propellant so it is about as dangerous as you r deuterium cylinder.
hope this helps

Re: Dangers of A Deuterium Cylinder

Posted: Mon Jun 02, 2014 3:12 pm
by Dennis P Brown
I strongly disagree that the dangers of deuterium is comparable to Butane - deuterium is highly explosive at most mixtures in air (hence, while flammability is similar to deuterium that isn't the issue for the primary danger of any flammable gas mixture.) Other flammable gases like butane have a considerably smaller/narrower explosive mixture range (in fact, except for a very small mixture range near the end points, deuterium is explosive over almost all mixture levels.) So it is critical that all tubing connecting deuterium to the system be pressure tested for leaks. A deuterium (or hydrogen) leak resulting in any significant amount of gas release can be highly dangerous due to the extreme eases of ignition of deuterium and huge explosive range of mixtures in air.

Re: Dangers of A Deuterium Cylinder

Posted: Mon Jun 02, 2014 3:28 pm
by Richard Hull
Few here ever get to the deuterium stage. Those that do realize the issues, run lines at regulated ultra low pressures that are naturally well sealed...........Not to avoid explosions, but to save that expensive and precious gas.

All vacuum pump exhausts contain all the hydrogen ever admitted to the fusor and most everyone vents this to their room air via an oil vapor filter. Result? .....Not one hydrogen explosion as the room air receives 100% of all the deuterium consumed by the fusor.

I think this has never been brought up due to the fact that so little deuterium is used in a fusor and thereafter fully exhausted into the experimental environment. Smart folks realize no such explosive mixture could form due to the paucity of the lab released gas.

I have always vented my pump to the outside air beside my lab solely to avoid the slightest trace of the oil vapor from the pump settling on my lab gear and in my lungs. I have never considered the, included, exhausted deuterium an issue.

Richard Hull

Re: Dangers of A Deuterium Cylinder

Posted: Mon Jun 02, 2014 5:53 pm
by Chris Bradley
Dennis P Brown wrote:I strongly disagree that the dangers of deuterium is comparable to Butane - deuterium is highly explosive at most mixtures in air (hence, while flammability is similar to deuterium that isn't the issue for the primary danger of any flammable gas mixture.) Other flammable gases like butane have a considerably smaller/narrower explosive mixture range
Actually, I think containerised butane/propane is notably more dangerous. You are missing the "boiling liquid expanding vapor explosion" (BLEVE) mechanism.

But firstly, let's deal with the explosion limits: Yes, the LEL/UEL of hydrogen is wider than butane, but that is not how gas is typically ignited in a leakage accident. In an accident, gases will diffuse away from the source, and if there is an ignition source then it matters little what the UEL is, it is only the LEL that really matters because it will burn from the outside in, so to speak, one it meets an ignition source.

In this regard, hydrogen has a significantly higher LEL, so in principle if you have a detector then you'll get more warning of the H2 leak than the butane.

OK, so in one way you have a point that if the room fills with either hydrogen or butane that, if you did not suffocate when you walked into the room, throwing a switch might more likely cause the H2 to go off. But there is so little gas in a D2 lecture bottle that this would never happen. You would only ever be looking at the LEL, and it is actually significantly higher for H2. You could empty the whole lecture bottle out into a domestic room and I'd doubt you'd be able to get it to ignite unless you deliberately put a match to the exit valve. 18% LEL means that 50 litres will be diluted below ignition in a volume of just 0.25 m^3! Yup, the LEL suggests you can deliberately vent a whole bottle of D2 into a box of just 10 cubic feet and you'd not be able to get it to explode! Give it a try!

OK, so now onto the problem with butane/propane. Such containers can suffer BLEVE if they are, themselves, caught in a fire. This is where their temperatures reach a critical point at which the internal pressure of the boiling vapour ruptures the tank. This is why fire crews will firstly hose down any LPG tanks on a scene in a fire, because these are a huge explosion risk when heated. Hydrogen, stored as a compressed gas cylinder, will never suffer from BLEVE and is, in a relative sense to a butane cylinder, 'safe' in a fire as it cannot explode in that way and should remain safe so long as the valve survives the heat.

Butane - actually more dangerous by some margin, IMHO.

FWIW, I have installed a flammable gas monitor in my experimental areas, not for D2 flammability issues but to make sure I don't waste any in a leak and for any other flammable gases that I might happen to cause. These can be obtained very cheaply off ebay. Here's one (no connection with vendor): http://www.ebay.co.uk/itm/250995075737 . They use a ceramic sensor that is mass produced and quite robust, though you have to run it for several hours before it starts reading flammable content correctly. Fitting this should allay any fears whatsoever of an overly anxious parent, if any remains after realising that venting 50 litres of deuterium into a 2' box would already dilute it sufficiently that it can't explode!

(You say '25L'. You need to be clear if you're talking about a 25L tank volume, or 25L of deuterium gas?)

50L of deuterium gas is a truly paltry volume of the stuff. I trust I have beaten this non-issue to a fine gauge!

Re: Dangers of A Deuterium Cylinder

Posted: Mon Jun 02, 2014 8:56 pm
by Liam David
Definitely 25L worth of gas. Thanks for the answers-helped a lot.
-Liam David

Re: Dangers of A Deuterium Cylinder

Posted: Tue Jun 03, 2014 4:04 am
by AllenWallace
Have you considered the PEM fuel cell method of generating D2? Cheap and safe compared to a bottle of gas.
-Allen Wallace

Re: Dangers of A Deuterium Cylinder

Posted: Tue Jun 03, 2014 10:50 am
by Liam David
I have considered use of a PEM cell to generate gas, but decided not to due to the simplicity of using a bottle. I might construct such an apparatus when I have completed a neutron producing fusor.
-Liam David

Re: Dangers of A Deuterium Cylinder

Posted: Tue Jun 03, 2014 1:12 pm
by Dennis P Brown
Chris, you are missing a key property of deuterium - density. It will quickly rise in air and collect in a room's highest point and will not dilute as readily as butane. Maybe this property causes the deuterium to leave, maybe not. In which case an explosive mixture can easily collect in a room's highest point and will not necessarily dilute like a far denser gas like butane (which presents its own special hazards which really are not relevant to this topic at all; and frankly,should not even be addressed since this will just confuse most people when we should be focusing on the safety issues of the one gas fusors do commonly use - deuterium.)

As for ignition source, that is a very different matter and not the main issue here. I do agree such an event would rarely occur (yes, there are possible ignition sources exactly where most deuterium would likely collect - i.e.: located in ceilings, called lights - but those are unlikely to cause ignition.) Still, the bottom line is that isn't how safety works. One does not assume if ignition sources are unlikely to cause ignition/ an explosion than it is allowable to vent deuterium into a room with no regard to the amount. Yes, venting the entire lecture bottle of deuterium in an average sized room with typical ceilings would most likely not result in an explosion or fire but that isn't now one approaches safety.

Last I checked what I said is accurate and cautious; good advice for the average user - pressure check the deuterium lines for leaks. Deuterium is NOT like nor as safe as butane (it has a far larger explosive range and its threshold for ignition by sparks/fire sources is lower than butane's.) If that warrants multiple paragraphs and detailed arguments than I think this is getting too far from the basic question - is deuterium safe to use in the average home by someone who has essentially zero experience with explosive gases, or experience/knowledge of safe plumbing techniques for pressurized systems that use explosive gases.

Chris, as for a gas detector for a room, certainly a good idea; but for the extensive reasons you cite, I'd think not essential for a standard size lecture bottle if one is careful to test all lines on the pressure side of the system for leaks.

As for vacuum pump exhaust, of course I never mentioned or addressed that topic because it is irrelevant for the exact reasons that Richard cited - the working amount used by a fusor is nil. I only noted that the plumbing must be pressure tested and if anyone here thinks that is not a good idea than they are incorrect.

Re: Dangers of A Deuterium Cylinder

Posted: Tue Jun 03, 2014 4:52 pm
by Chris Bradley
Dennis P Brown wrote:Chris, you are missing a key property of deuterium - density. It will quickly rise in air and collect in a room's highest point and will not dilute as readily as butane.
Not wishing to carry on flogging, but it is a quiet day ... am I missing that property? 50L would form a layer of D2 that is 3mm thick if it were all to rise evenly and distribute itself on the ceiling of a small 12' square room. Do you really think a 3mm layer of rising gas would not dilute as it rose? I'm pretty confident it is such a small amount that thermal motion of the room's gases would instantly diffuse it, if it ever managed to get there without diffusing.

Maybe butane, on the other hand, which is a heavy gas, will tend to settle to the floor, or in some open container where it may concentrate, where it is less liable to diffusion from upward thermal motion. 50L of butane (2 mols, or 100g = 6MJ) actually sounds more dangerous for not mixing than 50L of D2 (= 0.5MJ).

I'm not advocating anyone tries to vent flammable gas into anywhere and try to set light to it, but I would suggest that the bigger risk with 50L of gas at 100 bar is the chance for lines to rupture and fly out, hitting you in the eyes with hoses and debris particles.

As it happens we have an empty, small lighter for the cooker which I have just refilled. I have just measured the mass of butane added and it is a tad over 2g. So the energy equivalence to 50L deuterium is actually 5 lighters worth, or in Liam's 25L case, under 3 lighters worth. So, Liam, the answer is that if your dad is prepared to consider having 3 small, filled, butane lighters in his basement then the D2 is certainly no more risky, and in practice much less risky as the cylinder will have much better valve parts and will leak less than the lighters.