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Vacuum Chamber (potential safety issue)

Mr. Skinny

Alien Cryogenic Engineer
Mr. Skinny
Joined
Dec 4, 2001
Messages
7,843
I’m looking for some help/opinions on a potential safety problem where I work.

At issue is a vacuum chamber. It is 20 ft. (6.096 meters) in diameter and 27 ft. (8.2296 meters) high. It has a domed top, which contains a flanged port capable of accepting a transparent window. The diameter of the window will be 4 in. (0.1016 meters)

The chamber will be pumped down to a vacuum of 10-6 (ten to the minus sixth) torr. (0 atmosphere/0 in. mm/ 0 kilobar)

I’m trying to determine if it is safe for someone to be present on a catwalk that encircles the domed top of the chamber, in the event the window fails. Should the window fail, would there be injury to someone’s ear drums? Would they be sucked toward the window port? Is everything that’s not tied down (equipment, dirt, pens/pencils, etc.) going to become dangerous projectiles?

BTW, one can assume there is sufficient make-up air to fill the chamber without asphyxiating anyone. It is located in a rather large, 50 ft. high bay.

The easy solution to the problem is to collect the data remotely, but this would significantly increase the expense.

Essentially, I’m looking for some logical rationale for approving or disapproving the presence of personnel on the catwalk, but frankly, I don’t understand the physics/dynamics of the failure event, so I’m finding it impossible to assess the probability and severity of the event; thus I can’t do a reasonable cost/benefit analysis.

Any help would be appreciated.
 
No danger. The vast majority of the glass will implode into the chamber (but you already knew that, I'm sure). Safety glasses would be a good idea if going nearby, though.

As for any dynamic air effects, the total pressure difference is only 15 psi, so there will be no distant "suctioning" effect. Might be loud, though, as for a few moments there will be a lot of air trying to get in there. But no, no danger of things flying off shelves, people being sucked through (like in Goldfinger) or anything. Just take normal safety precautions such as the safety glasses and use glass rated for vacuum service.
 
Gary is correct. Most bio and hazmet labs use a negative pressure differential to contain any contagion or other contaminant, rather the venting to the outside of the contained area it is filtered or captured by special air handlers.

Even a catastrophic failure ( such as the port shattering) would produce only minor effects. The likelihood is that an air leak would happen and be repaired long before any structural failure.

The financial analysis can only be determined by someone who knows construction costs, how the chamber is used and what the constraints of the intended use provides in dollar amounts.
 
Why not just use transparent aluminum?

Oh, nevermind. I forgot it hasn't been invented yet.

"A keyboard! How quaint!"
 
I would imagine that there are some significant safety issues here. I don't have any experience with vacuum chambers as such, but thinking about it logically:

If there was a sudden catastrophic failure of the glass, there would of course be an implosion. However, the implosion would lead to a secondary outgoing shock wave which is effectively the front of an EXplosion. I would imagine that the shock wave in the air alone would create a very loud bang and could possibly cause a ruptured ear drum or ruptured peripheral blood vessels (i.e. in the nose) in anybody near to it. Secondly, the secondary shock wave could carry particles on the wave front. I recall when I was a child throwing a stone at an old cathode ray tube (vacuum tube) from a TV. The thing imploded, and then threw bits of glass outwards for about 20 feet or so.

Remember that thunder is effectively the secondary shock wave of an implosion. When lightning strikes it rarefies the air and the collapse of air into the rarefied region causes the thunderclap. So I wouldn't rule out the same possibility here - although on a smaller scale of course.

The chamber itself would probably stop most of the glass fragments from shooting outwards in all directions, but there is a possibility that some could be ejected through the broken port.
 
I don't know anything about vaccum chambers but i do know a bit about health and safety.

We assess all safety hazards using a 5x5 matrix.

First you assess the likelehood of the risk occuring, rated 1-5, 1 being an exceedingly rare chance of occurance, 5 being almost certain, scaled inbetween.
Second you assess the potential damage should the incident occur, with 1 being a minor injury (eg cut, no mininal disruption to work etc) and 5 being a fatality.
Third you mulitiply the two numbers together to get your risk factor. If this is 8/9 or above then it is judged to be a risk that requires investigation, above 15 and you have to stop the activity.
I'g guess you'd be looking at a 1 or 2 for chance and 4 or 5 for damage.
You can probably get an example matrix on the internet somewhere. Write it up, with a nice colours and it will look impressive!
Yes it is subjective :)

If the risk is below 8/9 it doesn't mean you can ignore it.

The chief aim of health and safety is avoidance of the danger. If you consider that there is a risk associated with being on the catwalk, then i'd do a matrix, write up, point out that the consequences of an accident are severe and suggest that it is easily avoided by a simple policy change, ie when chamber in use, no one on the catwalk.
 
Thanks for the opinions. It sounds to me that the risk should be relatively moderate, much of which can be abated by safety glasses, hearing protection, and maintaining maximum seperation between the window and personnel.

Prester John , I'm a Safety Engineer. I'm well aware of probability/severity risk assessment matrix evaluations. :) . I'm posing the question here on the fourm because I didn't have a very good feel for what the severity of the incident might be. I'm pretty sure that if the window fails, all of the pieces would be sucked into, and contained within, the chamber, so I'm not too worried about that. I'm just trying to get a feel for whether there would be a loud bang and a little bit of air rushing in, or whether it would be like trying to stand on the seashore in the face of hurricane force winds.

Thanks again to those that commented. I'm willing to entertain any other opinions, if anyone has one.
 
I guess that counts as teaching your grandmother to suck eggs then.
 
Okay, maybe I'm thinking of the wrong thing or something, but I would say there is very little to no danger, even should someone have their face in the glass when it fails.

It's a vacuum chamber, right? Not a pressure chamber? Than ANY failure that could possibly happen is going to produce no more than a 1atm pressure difference. Period. You'd have a bit of wind, but nothing extreme (AIU). The thing to remember is that the wiund, suction, pressure, etc, come not from the vacuum chamber pulling in but from the outside ait pushing in. Since the outside air is at 1atm, that's the figure to use. I'm sure you could take this and go on to estimate various wind speeds and such dependant on the size of the hole, I don't know enough of the mathematics to figure that. But I don't think 1 atm is going to be catastrophic.
 
I'm no engineer, nor am I a doctor, nor did I sleep at a Holiday Inn last night, but I would think that if someone's face were right in the glass (or, say, if they were sitting on it) that a sudden failure of the glass would be ugly. I mean, how much pressure can it possibly take to suck someone's internal organs out?

On the other hand, I think if you were a few feet away you would probably be pretty safe.... maybe you should put some sort of guard around the opening?
 
JSFolk said:
I'm no engineer, nor am I a doctor, nor did I sleep at a Holiday Inn last night, but I would think that if someone's face were right in the glass (or, say, if they were sitting on it) that a sudden failure of the glass would be ugly. I mean, how much pressure can it possibly take to suck someone's internal organs out?
Click to expand...

The pressure isn't going to suck anything out. A 4" hole in that big of a chamber will not cause a problem with loss of room pressure.

OTOH, someone near the opening will be knocked into pretty dang hard by the push of the gas behind them. They'll get knocked out and have a concussion, but they won't have any organs sucked out (unless their face plugs the hole)
 
Huntsman said:
Okay, maybe I'm thinking of the wrong thing or something, but I would say there is very little to no danger, even should someone have their face in the glass when it fails.

It's a vacuum chamber, right? Not a pressure chamber? Than ANY failure that could possibly happen is going to produce no more than a 1atm pressure difference. Period. You'd have a bit of wind, but nothing extreme (AIU). The thing to remember is that the wiund, suction, pressure, etc, come not from the vacuum chamber pulling in but from the outside ait pushing in. Since the outside air is at 1atm, that's the figure to use. I'm sure you could take this and go on to estimate various wind speeds and such dependant on the size of the hole, I don't know enough of the mathematics to figure that. But I don't think 1 atm is going to be catastrophic.
Click to expand...

Even 1 atm can be pretty catastrophic.

From: http://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=14321087

Accident: 14321087 - Employee Killed When Vacuum Chamber Implodes

Employee #1 went into a vacuum chamber testing area to look through the porthole opening in a pressurized vacuum chamber and observe the condition of a nose cone that was being tested. The 12 in. diameter glass in the porthole opening imploded, causing Employee #1's head and one arm to be pulled into the vacuum chamber. He died of crushing head injuries and asphyxia.

That was a 12 inch port of course. What worries me more about the case in question (which is a 4 inch port), is the shock wave AFTER the initial implosion. I suspect that porthole will act pretty much like a small cannon when the outgoing shock wave hits. It's a pretty large chamber, and there will be quite a bit of energy from the inrush of air which will have to go somewhere afterwards.

Although maybe the relatively small hole will slow down the inrush somewhat enough to damp some of the shock wave. Don't know. But personally I wouldn't like to be anywhere near it! :)
 
Interesting differences in opinion here, but that's why I ask for them.

FYI, the proposed situation would have the employee stationed at least 15-20 feet away from the window.

Someone suggested guarding it to prevent full body contact. I think that's an excellent idea. I just have to make sure the guarding doesn't interfere with the "transparency" of the window.
 
Pragmatist said:

Employee #1 went into a vacuum chamber testing area to look through the porthole opening in a pressurized vacuum chamber and observe the condition of a nose cone that was being tested. The 12 in. diameter glass in the porthole opening imploded, causing Employee #1's head and one arm to be pulled into the vacuum chamber. He died of crushing head injuries and asphyxia.[/I]
[/B]
Click to expand...

He was close to the hole when the implosion occured, and the rush of gas pushed him into the vacuum chamber and knocked him out along the way ("crushing head injuries").

This is basically what I said would be possible above. However, the difference is that with a 4" hole, his head won't get sucked in. It will get smashed against the chamber and knock him out, outside the chamber. Therefore, he won't asphyxiate.

If the walkway is 10 - 15 ft from the viewport, nothing serious would happen.
 
OK, I think I'll allow them to be up there (15 ft or so away).

I'll have to require the personal protective equipment, guarding over the opening perhaps; chain off the area within 15 ft of the opening; and probably think about making them wear some fall protection as well (even though it already has guard rails, etc.).

Thanks to those that responded to my "sanity check" query.
 
pgwenthold said:


The pressure isn't going to suck anything out. A 4" hole in that big of a chamber will not cause a problem with loss of room pressure.

OTOH, someone near the opening will be knocked into pretty dang hard by the push of the gas behind them. They'll get knocked out and have a concussion, but they won't have any organs sucked out (unless their face plugs the hole)
Click to expand...

Sorry, I should have made that a little more clear. When I said "unless they have their face right in the glass" I meant right up against the glass. Thus, when the glass broke, they would be pushed against the hole, blocking it, and leading to possible organ-hoovering.

Seriously, though, I don't think fall protection equipment would be necessary for folks 15-20 feet away from the opening. I doubt they would even feel air movement.
 
I agree with the hearing protection, though. The rushing air could cause hearing damage. So goggles and muffs (or plugs) should do it (as well as keeping back at least six feet or your fifteen).
 
I'm NOT going to sit down and figure this out. You need to get an acoustic safety consultant and examine this very, very carefully.

Don't forget, 1 atmosphere is 192 dB SPL. You can't really do that, of course, but your "base level" here is something like 192dB SPL, which is so far past the level of instant hearing damage I don't even want to think about it.

GET AN EXPERT, PAID, LIABILITY-INSURED OPINION.

And anyone giving advice here other than that, frankly, is, I think, out of their gourd.
 
jj said:
I'm NOT going to sit down and figure this out. You need to get an acoustic safety consultant and examine this very, very carefully.

Don't forget, 1 atmosphere is 192 dB SPL. You can't really do that, of course, but your "base level" here is something like 192dB SPL, which is so far past the level of instant hearing damage I don't even want to think about it.

GET AN EXPERT, PAID, LIABILITY-INSURED OPINION.

And anyone giving advice here other than that, frankly, is, I think, out of their gourd.
Click to expand...

Seconded!
 
jj said:
I'm NOT going to sit down and figure this out. You need to get an acoustic safety consultant and examine this very, very carefully.

Don't forget, 1 atmosphere is 192 dB SPL. You can't really do that, of course, but your "base level" here is something like 192dB SPL, which is so far past the level of instant hearing damage I don't even want to think about it.

GET AN EXPERT, PAID, LIABILITY-INSURED OPINION.

And anyone giving advice here other than that, frankly, is, I think, out of their gourd.
Click to expand...
Wow! 192 dB sound pressure level? That's impressive.
I don't really understand what you mean though (1 atm is 192 dB SPL). Is there any way you can simplify this statement for the untrained?

If there is a possibility of sound pressure levels that high being created, then I'll have a serious problem to contend with.

Gaaah....I guess you can see why I feel so unsure of myself here. This could turn into a real sh!tstorm. The vacuum chamber is government owned.......the people who operate it, and will be exposed to any hazard, are contractors.

Guess I better call the JAG office on Monday and figure out who is ultimately responsible for making the call on this.

Again, thanks to everyone for their thoughtful comments.
 
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