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!