I was using hydrogen chloride gas straight out of the cylinder today, first time I've done that in many years. That's a very different substance from regular hydrochloric acid, which is technically a solution of HCl gas in water. The straight stuff will really snap your head back if you get a whiff of it, which you'd better not since it does Bad Stuff to your lungs, as you'd imagine.
You need to rig up a trap for the vented gas, since it's rather bad form just to send it up the fume hood. The standard way is to bubble the excess through aqueous base to neutralize it, preferably rigged up so that the water doesn't have a clear path to go siphoning back into your reaction if the pressure goes haywire. Bubbling the HCl into a solvent like methanol always looks a little odd. You can send a pretty vigorous stream of the gas in one side and have very little coming out through the trap at all, since the methanol is soaking up so much of it.
These gas cylinders are under pressure, and the large ones look just like the helium tanks that non-scientists are familiar with from balloon vendors. The regulator valves on top of them need to be made of rather more robust material for an HCl tank than for helium - which is, after all, totally inert under all conditions short of the interior of the sun. Back in grad school, a corroded regulator (on a whopping big HCl cylinder) gave me a real scare as it threatened to give way and vent all the gas at the full tank-neck pressure of about 1500 psi. I had to go sit down for a while after that one.
But today's work was with a lecture bottle, a much smaller cylinder that holds only a couple of hundred grams of the gas. That's enough to do some damage, true, but not on the scale of the free-standing ones. I saw that happen back in graduate school as well. One day I was sitting in the library, looking up some references, when I noticed the occupants of the third floor research labs pouring out onto the lawn from the rarely-used side stairwells. They were hustling right along, too, which suggested some sort of liveliness upstairs.
As it turned out, it was in the lab next door to mine. One of the guys had another HCl tank, a medium-sized one, which was also corroded and jammed. He went for the cylinder wrench, which he then used for the non-standard purpose of vigorously whanging the valve with strong overhand strokes. One of the other guys in the lab summed up the sound of this process as "PING. . .PING. . .PING. . .hisssssSSSSSSS oh @!?#!"
The hood wasn't enhanced by having a kilo or two of hydrogen chloride vented all over it, that's for sure. It looked as if it had been subjected to some sort of accelerated aging process - if there were a market for antiquing lab equipment, this would be a good way to do it. All the exposed metal was pitted and flecked with green. The stainless steel was hazed with rust, having reached its carrying capacity for corrosion. And everything still had a fine mist of concentrated hydrochloric acid all over it where the gas had sucked the water out of the air and condensed on the nearest surface. Cleaning it up is not the way you want to spend your Friday afternoon.
None of that for me today, though. I ran the stuff in uneventfully, with the reaction turning to a clear yellow, which is nothing compared to the colors I'd turn if you sprayed that much on me. I'll find out tomorrow if things have worked according to plan. One thing's certain: something will have happened. Nothing escapes from HCl gas unchanged.
1. The Novice Chemist on October 20, 2004 10:25 PM writes...
That may have been the most horrifying story I've heard from you yet, Derek.
Does anyone have anyone good stories about out-of-control gas cylinders? I've heard they're like torpedos, but I've never actually seen one in action. (I don't think I want to, either.)
Permalink to Comment2. otey on October 21, 2004 10:28 AM writes...
Delightful stories. I'm glad they had happy endings.
Permalink to Comment3. Paul on October 21, 2004 10:38 AM writes...
As a non chemist, I wonder how often really bad things actually do happen to chemists. Is it a fairly hazardous job in general? Has anyone ever looked at occupational injuries of chemists and compared them to, say, road construction workers? How about looking at long term cancer rates for the profession?
I think I would like to know these things if I was a chemist.
Permalink to Comment4. Derek Lowe on October 21, 2004 11:18 AM writes...
Y'know, it's not a job without hazards, but the last data I recall seeing were pretty reassuring. No increased cancer risk, and pretty long life expectancy - I'll try to dig up the figures. Of course, if you happen to run into the wrong compound, that could change. . .
Permalink to Comment5. Drew on October 21, 2004 2:31 PM writes...
Derek, I am surprised you saw data showing no increased cancer risk. I had always been extrapolating from the old school we-bathe-in-benzeze days, assuming there must be some greater incidence of cancer.
My personal almost-armaggeddon? A 50-mL plastic syringe (dumb in retrospect) full of chlorosulfonic acid, magically tearing open under pressure and ejecting an enormous jet of concentrated nastiness...thankfully toward the *back* of the hood!
Permalink to Comment6. Derek Lowe on October 21, 2004 3:39 PM writes...
Well, chlorosulfonic acid won't give you cancer, anyway. Permanent tissue burns, yeah, but not cancer. And you're right, those polypropylene syringes, although they'll put up with a lot, really don't stand up too well to the stuff - one of my colleagues had a similar experience to yours, and he didn't enjoy it much, either.
Permalink to Comment7. Chris Hoess on October 21, 2004 11:58 PM writes...
Gas cylinders, hmm. Never personally witnessed one of those, but a friend worked at the Naval Research Laboratories at one point and saw the aftermath of one lost-the-valve incident. Apparently it flew through a cinder block wall, across a lab, through another cinder block wall, and ricocheted around in that lab for a while before coming to rest. Must have been after-hours, or something, as I don't believe anyone was killed.
I'm surprised Derek sat around in the library to watch the exodus; my normal assumption on seeing people make a rapid exit from a chemistry building is that they have a darned good reason to be doing so and that I should join them.
Permalink to Comment8. w.h. on October 22, 2004 2:28 AM writes...
Ouch.
They spent a bunch of time in welding class talking about what to do with gas cylinders. How one does *not* want to deal with a corroded tank, regulators, etc. We were cautioned to never ever have the cylinder be in a situation where it could fall over and break the valve stem -- it must be chained to the wall. I might add that the crazy artists I know, who tend towards the cavalier side of safety, are still sticklers about gas cylinders. Well, except when they put wheels on them and set new world records in the unlimited category of Power Tool Drag Racing. ;)
And, of course, with us folks who weld and do plasma art with inert gasses, there's the always fun situation of displacing enough oxygen to create the cloud of death. Apparently this happens in shipyards, where one guy suddenly collapses because there's no air left. And then his buddy goes in after him. Which usually ends up killing them both. The fun bit is that if it's one of the inert elements, your body doesn't even realize what's going on because it's too closely tuned to elevated-CO2 situations and not closely enough tuned to no-O2 situations. I'm glad to say I've never dealt with that one.
There's some good stories interspersed through:
Permalink to Commenthttp://yarchive.net/metal/accidents.html
9. jwax on October 23, 2004 8:36 AM writes...
Being scuba divers, both my roommate and I retired for the night, leaving our tanks in their usual place, the living room of our tiny apartment. A few hours later, we awoke to the loudest, ear splitting hiss imaginable. One of the 2500 psi rupture plugs had failed, and the full tank was doing an incredible dance around the room, moving furniture with every whack and deflection! The roar of air was deafening!We stayed low while watching the dance as the only other exit was a window, and the violent sight was actually, kinda cool! It crashed and banged for 2-3 minutes, loading itself down with an encrustation of thick ice, and exhaled its (and ours) final relief in front of a tissue box, calmly launching them, one after the other into the cold air! Whew!
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