Vacuum Chamber (potential safety issue)

[Mr. Skinny]

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.

[garys_2k]

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.

[TillEulenspiegel]

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.

[TeaBag420]

Why not just use transparent aluminum?

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

"A keyboard! How quaint!"

[Pragmatist]

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.

[Prester John]

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.

[Mr. Skinny]

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.

[Prester John]

I guess that counts as teaching your grandmother to suck eggs then.

[Hellbound]

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.

[JSFolk]

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?

[pgwenthold]

Originally posted by JSFolk
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?



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)

[Pragmatist]

Originally posted by Huntsman
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.

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! :)

[Mr. Skinny]

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.

[pgwenthold]

Originally posted by Pragmatist

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]

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.

[Mr. Skinny]

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.

[JSFolk]

Originally posted by pgwenthold


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)

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.

[garys_2k]

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).

[jj]

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.

[Pragmatist]

Originally posted by jj
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.

Seconded!

[Mr. Skinny]

Originally posted by jj
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.
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.

[ktesibios]

[QUOTE]Originally posted by Mr. Skinny
[B]
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?

QUOTE]

SPL is measured in decibels referred to a pressure variation of 20 uPa, i.e., 0 dB SPL = 2 x 10 ^-5 Pa sound pressure.

Normal sea level atmospheric pressure runs around 101 kPa. Assuming that the sound pressure created by the failure of the glass in the vacuum chamber would be equal to the pressure difference between the outside and the inside, we would have a peak sound pressure of 101 kPa.

To turn that into a dB SPL figure, you use db SPL = 20 log (P1/Pref), or 20 log (1.01 x 10^5/2 x 10^-5).

I get approximately 194 dB SPL, or, in really technical terms, a freakin' loud noise, much, much louder than what a shooter firing a rifle or pistol is subjected to.

The consequences for your safety regime might be as simple as requiring that anyone present in the chamber room wear appropriate hearing protection, or they might be more serious.

I can't say. I agree wholeheartedly with jj- get an expert opinion from someone who assesses acoustic safety professionally.

[Mr. Skinny]

Originally posted by ktesibios
SPL is measured in decibels referred to a pressure variation of 20 uPa, i.e., 0 dB SPL = 2 x 10 ^-5 Pa sound pressure.

Normal sea level atmospheric pressure runs around 101 kPa. Assuming that the sound pressure created by the failure of the glass in the vacuum chamber would be equal to the pressure difference between the outside and the inside, we would have a peak sound pressure of 101 kPa.

To turn that into a dB SPL figure, you use db SPL = 20 log (P1/Pref), or 20 log (1.01 x 10^5/2 x 10^-5).

I get approximately 194 dB SPL, or, in really technical terms, a freakin' loud noise, much, much louder than what a shooter firing a rifle or pistol is subjected to.

The consequences for your safety regime might be as simple as requiring that anyone present in the chamber room wear appropriate hearing protection, or they might be more serious.

I can't say. I agree wholeheartedly with jj- get an expert opinion from someone who assesses acoustic safety professionally.
Thanks, ktesbios. That explaination helps a bit.

I'll have to look into the hearing protection issue further, but if memory serves, even the best hearing protection only offers a noise reduction rating (NRR) of about 28-30 dBA. Even if you doubled them up, e.g. ear plugs with headset muffs over the top, I'm not sure it would be sufficient protection.

I'm not sure if NRR's are strictly additive when used in combination. I'm also not sure what NRR I'd need to prevent damage from an "instantaneous" event such as a window failure.

We have a (company internal) standard of 85 dBA over an eight hour time weighted average. While I'm sure the noise from this failure event wouldn't exceed that limit due to it's short duration, it certainly seems as though some damage could be done due to a sudden peak SPL like the one described.

I appreciate that everyone is recommending a professional acoustic expert, but for now I'll look at some less expensive methods of abating the hazard. If I get backed into a corner over technical issues, I'll definitely recommend one.

[Badger]

As an engineer, my first thought is "Hire a professional to evaluate this."

I have questions pertaining to the certification of this pressure vessel. Who inspected it? When? Is it up to date? What is the window rated for? When was it certified? Is it up to date?

That is aside from the analysis of the forces invovled.

So, if you don't have the expertise to evaluate this yourself, hire someone who does have that expertise. There is life and liability invovled, and it's always better to be safe than sorry.

If you're the guy who'se responsible for the project, and something goes wrong, you better have taken all reasonable precautions.

There's a large amount of energy in the volume of air you describe. Don't mess with it. Be sure. Things can get very bad, very fast.

Best of luck!

[Mr. Skinny]

Originally posted by Badger
As an engineer, my first thought is "Hire a professional to evaluate this."

I have questions pertaining to the certification of this pressure vessel. Who inspected it? When? Is it up to date? What is the window rated for? When was it certified? Is it up to date?

That is aside from the analysis of the forces invovled.

So, if you don't have the expertise to evaluate this yourself, hire someone who does have that expertise. There is life and liability invovled, and it's always better to be safe than sorry.

If you're the guy who'se responsible for the project, and something goes wrong, you better have taken all reasonable precautions.

There's a large amount of energy in the volume of air you describe. Don't mess with it. Be sure. Things can get very bad, very fast.

Best of luck!
There is no problem with the pressure vessel, badger. Among other things, I'm a certified boiler and pressure vessel inspector :) . Vacuum chambers are not considered "code" vessels though for the most part since code doesn't apply unless you pressurize above 15 psi. The window itself is not certified per se, other than through experience with viewports on vacuum chambers (which are quite common where I work).

I'm not responsible for the project, but I am responsible for evaluating the risk (severity/probability) and recommending what actions need to be taken to make the risk acceptable to management. Since I didn't have a good feel for what could happen, I posted here to get the opinions of the smart people here.

I've got a few months to gather information, and my decisions won't be rushed, I guarantee you.

Appreciate your input though. Thanks.

[Tez]

Anecdotal evidence:

As a PhD student, I had a roomate who did experiments using a similar sized chamber at lower pressure and with several windows. We never gave it a second thought. Two people had desks beside the chamber, people were in and out of that lab all the time.

But hey, we'd have all put our life on the line for the cool physics they were doing :) (which apparently culminated in the best measurement of the fine structure constant to that time....)

[jj]

Originally posted by Mr. Skinny

Wow! 192 dB sound pressure level?

Bleah! It's 194dB SPL for a 1 atmosphere RMS sound wave, of course, like K said.

That is, of course physically impossible, you can't get the negative part, but the peak "loudness" of your event at the window at the break can approach that "level", although it's going to be so nonlinear that calling it a "level" is a joke.

But you need a formal assessment. Get it!!!!

[TeaBag420]

Originally posted by JSFolk
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?



More than one atmosphere. Have you ever kissed a girl?

[TeaBag420]

Originally posted by Pragmatist


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! :)

And what exactly is a "pressurized vacuum chamber"? Off with her head!!

[TeaBag420]

Originally posted by ktesibios
[QUOTE]Originally posted by Mr. Skinny
[B]
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?

QUOTE]

SPL is measured in decibels referred to a pressure variation of 20 uPa, i.e., 0 dB SPL = 2 x 10 ^-5 Pa sound pressure.

Normal sea level atmospheric pressure runs around 101 kPa. Assuming that the sound pressure created by the failure of the glass in the vacuum chamber would be equal to the pressure difference between the outside and the inside, we would have a peak sound pressure of 101 kPa.

To turn that into a dB SPL figure, you use db SPL = 20 log (P1/Pref), or 20 log (1.01 x 10^5/2 x 10^-5).

I get approximately 194 dB SPL, or, in really technical terms, a freakin' loud noise, much, much louder than what a shooter firing a rifle or pistol is subjected to.

The consequences for your safety regime might be as simple as requiring that anyone present in the chamber room wear appropriate hearing protection, or they might be more serious.

I can't say. I agree wholeheartedly with jj- get an expert opinion from someone who assesses acoustic safety professionally.


So where would children's party balloons bursting rate on that scale?

[garys_2k]

So, is the issue the SPL difference between a very hard vacuum and atmosphere, or the amount of sound created by atmospheric air being drawn into the chamber through an irregular opening?

True, if you situated your head in such a way that one side of your eardrum was in the atmosphere, and the other was in the hard vacuum, you'd have this incredible pressure. Granted. But I don't think that is the situation being presented here.

I would expect a rupture of the glass to create a BANG!, followed by possibly a shriek, as air rushed into the chamber. As the pressure in the chamber increases the tenor and intensity of the sound would change, generally becoming less intense with time.

I don't know how to calculate the amount of sound the rushing air could make, perhaps there are ways of doing so. But it is NOT the same as the 192-194 dB of the total pressure difference.

[Mr. Skinny]

That's kind of how I had envisioned it too garys2k, but I felt uneasy about assuming that.

I don't think the 192-194 dB figure is a prediction, but rather just a theoretical maximum, albeit one that deserves consideration (I mean, that's LOUD!)

And for TeaBag; I'd make a SWAG and say a childs party baloon bursting might be about 90-92 dB. It depends on the size of the baloon, how much pressure it contains, blah, blah....... (jj probably has a much better idea). :)

[TillEulenspiegel]

I would add my assent to jj's and others advice about consulting an expert. An acoustician will model the open space in the room and the chamber volume and all kinds of other factors ( reflectivity, structural materials in the room...) One thing tho the 192 db SPL is correct except that one of the most important factors -distance, is not taken into account. Normally acoustic measurements include relative distances from the source. The 192db figure represents the absolute maximum value of an ideal event a the point of origin.

Some other common measurements........130-150 dB SPL @ 100 feet behind airplane jet engine, train 70db SPL @ 100ft, pain 140db SPL. So the room will be plotted to give relative db SPL ( sound falloff, 6db per doubling of distance for a point source, the inverse square law) at specific points across the room or catwalk.
There's probably some pertinent OSHA standards as well you will have to consider.

Another thing to mention , can you retrofit the window with a hi density molecular plastic like lexan? Less of a chance of a catastrophic failure then even reinforced glass.

[Blue Monk]

Mr. Skinny,

I just want to know what you need a vacuum chamber for at Burger King?

[Mr. Skinny]

Till ,

I fully appreciate the advice you and others have given me to consult an acoustics expert. I will certainly do that it if it becomes necessary.

However, I currently still have the option of doing the data collection from a location that is remote from the catwalk. For example, I can require that personnel must be in a lightly constructed control room some 50+ feet away from the window, and could just as easily require them to be on the other side of a 6 foot thick reinforced concrete wall (in the next bay over.......also about 50+ feet away).

Taking one of these options seems less expensive than hiring an acoustics expert, though more expensive than doing data collection from the catwalk.

As for the window, it has to have certain transparency characteristics that will allow a laser beam of certain wavelength, etc. to pass. I leave that to the laser experts.

As to OSHA, there are no standards relating to vacuum chambers/windows to my knowledge.

[Fidelio]

Someone may have mentioned this already but a 4" obsevation window pretty much means ones nose has to be very near the thing in order to observe. Not a good situation I think. Maybe you should duct tape some steel armor over the window. :D

[edit to add] Oh lasers... umm never mind then.

[Mr. Skinny]

Originally posted by Blue Monk
Mr. Skinny,

I just want to know what you need a vacuum chamber for at Burger King?
Employee cranial cavity evacuation; liposuction to supply the deep fryers; general dry and wet vacuuming of the store, you know, that sorta thing.

You act like you never worked in a fast food joint, Blue Monk.

[Blue Monk]

Originally posted by Mr. Skinny

Employee cranial cavity evacuation; liposuction to supply the deep fryers; general dry and wet vacuuming of the store, you know, that sorta thing.

You act like you never worked in a fast food joint, Blue Monk.

Hey, that's a cheap shot.

I'm only 49. I'm sure I'll be moving up anyday now.

[jj]

Originally posted by Mr. Skinny
As to OSHA, there are no standards relating to vacuum chambers/windows to my knowledge.

There are, however, acoustic noise limits in OSHA regs.

[jj]

Originally posted by garys_2k
True, if you situated your head in such a way that one side of your eardrum was in the atmosphere, and the other was in the hard vacuum, you'd have this incredible pressure.

However, as you move away, this level will drop by distance. AT this kind of level, nothing is going to be remotely linear, and you need an expert who deals with shock waves, etc, to cope, rather than a simple acoustician.

The size of the room around it also matters, it will determine the mid-time drop in pressure before the outside room equalizes. It will also put some PSI load (without more specifics than I have, or want) on those walls temporarily, might pull in a window or something there if it's not a great big space around it.

In general, I think it's more dangerous than people assume, and I again repeat my suggestion to get a real expert opinion.

Consider, if the room has 13.7 times the volume of the vacuum chamber, you'll have a temporary 1 PSI drop until the room leaks back up. 1 PSI is, lessee, um, 144 lbs/sq foot. (cough) That also works out to about 170db SPL, although probably at a low frequency, not at midband ear sensitivity... This port is 4"? I haven't figured out the Helmholtz resonance, but it's going to be low, you may get quite a few (low frequency) oscillations as it fills up, too...

GET AN EXPERT OPINION DUDE!

[Mr. Skinny]

Originally posted by jj


There are, however, acoustic noise limits in OSHA regs.
Gotcha, 90 dBA Time Weighted Average, or PEL if you prefer.

Hey jj, what's your SWAG about the exposure to people in the area? Will the instantaneous noise level be so loud it will burst eardrums, even with hearing protection, or will it be a bang and a "noisy" rush of air.

You can PM me if you don't want to SWAG this in public.

Thanks.

Edited to add: Just saw the above post jj. Thanks. That's the kinda SWAG I'm looking for.

[jj]

Originally posted by Mr. Skinny

Gotcha, 90 dBA Time Weighted Average, or PEL if you prefer.

Hey jj, what's your SWAG about the exposure to people in the area? Will the instantaneous noise level be so loud it will burst eardrums, even with hearing protection, or will it be a bang and a "noisy" rush of air.

You can PM me if you don't want to SWAG this in public.

Thanks.

I'd be very, very worried about people being seriously injured, but again, GET AN EXPERT OPINION.

[Mr. Skinny]

Originally posted by jj


I'd be very, very worried about people being seriously injured, but again, GET AN EXPERT OPINION.
We were posting on top of each other jj, I already edited the post you quoted above.

Thanks.

[garys_2k]

If you're worried at all about depressurizing the room, an open window would supply all the air you'd need. Better yet, have the HVAC fresh air supply ducts locked open. All you're fighting is that 4" hole, it wouldn't take too large an opening to more than swamp it with supply ability to prevent significant negative pressure.

[jj]

Originally posted by garys_2k
If you're worried at all about depressurizing the room, an open window would supply all the air you'd need. Better yet, have the HVAC fresh air supply ducts locked open. All you're fighting is that 4" hole, it wouldn't take too large an opening to more than swamp it with supply ability to prevent significant negative pressure.

Should work, as long as there aren't any nasty resonances, but I think the problem goes well beyond simple depressurization.

[garys_2k]

Originally posted by jj


Should work, as long as there aren't any nasty resonances, but I think the problem goes well beyond simple depressurization.
Very true. Here's my off the hat list:

- Injury from flying glass. Although much of it would implode into the chamber, some fragments would likely be expelled with force. Suggestion for protection would be safety goggles.

- Room depressurizztion. Pretty easily prevented, as above. Danger could be significant, though, if precautions weren't taken and the chamber volume was a fair portion of the room and the room was modestly well sealed to the outside.

- Danger from flying objects/"being sucked into the hole." Not likely, as suction is a poor way to direct gas flow with significant velocity. Lots of designs must be put into hoods with significant airflow volumes to capture even vapors, so I'd have to put this near the bottom of the list. Keep people and their pens and pencils a few feet back and someone might have their hair mussed.

- Acoustic. The big one, and potentially nasty. There are lots of ways the glass could break, from an almost instantaneous total loss and implosion to a gradual degradation with slowly increasing opening size. Lot of things could happen here, from that very abrupt BANG! (could the glass be accelerated to faster than sound, could the inrushing air reach sonic velocity? I don't know, but I doubt it. <-- Not estimated or calculated, but 15 psi isn't much and most supersonic wind tunnels run at higher pressures).

Would it be "worth it" to get an expert's opinion? Maybe, but one would have to weigh the costs of that v. the probability of an accident. Where are you getting the glass? Could more than one layer be used? Is it shielded against objects falling on it? What are the total number of hours you would expect a person to be at risk over the lifetime of the experiment? If this is going to be a very long term study it may sway you to pay up to cover this base.

It's hard NOT to be very cautious, I know, but the budget has to be consulted. It's cheap enough to require hearing protection (I like to shoot recreation ally and use plugs and ANR 30 muffs together, they're very effective) but I suppose each situation is different.

[jj]

Originally posted by garys_2k

Very true. Here's my off the hat list:

- Injury from flying glass. Although much of it would implode into the chamber, some fragments would likely be expelled with force. Suggestion for protection would be safety goggles.


I'd not worry about the 4" port glass. I would worry about any windows in the main room.


- Room depressurizztion. Pretty easily prevented, as above. Danger could be significant, though, if precautions weren't taken and the chamber volume was a fair portion of the room and the room was modestly well sealed to the outside.


Even low levels of sudden pressure drop are rather more surprisingly dangerous than most people realize. I don't have a cite handy, but I'd be very careful on this one. Whatever you do, don't read about vacuum-cleaner accidents. (shudder) Well, do, for information, don't eat lunch first. Now, this thing isn't going to create any sustained vacuum, but I am not aware of a good threat model, to say the least.

It's hard NOT to be very cautious, I know, but the budget has to be consulted. It's cheap enough to require hearing protection (I like to shoot recreation ally and use plugs and ANR 30 muffs together, they're very effective) but I suppose each situation is different.

But don't forget that we're talking low to very low frequencies here, not high frequencies. This changes the rules. Ear protectors often don't work that well at VLF...

[Mr. Skinny]

Originally posted by garys_2k

Very true. Here's my off the hat list:

- Injury from flying glass. Although much of it would implode into the chamber, some fragments would likely be expelled with force. Suggestion for protection would be safety goggles.
This is unlikely IMO. The probability of any pieces from a 4 inch diameter window exiting through that same hole after being sucked into a 20 x 27 foot chamber seems remote.

- Room depressurizztion. Pretty easily prevented, as above. Danger could be significant, though, if precautions weren't taken and the chamber volume was a fair portion of the room and the room was modestly well sealed to the outside..
The chamber is located in a 50 ft high by 50 ft wide by 150 ft long, reinforced concrete bay. There is plenty of ambient air for the initial implosion, and it's leaky enough to allow for make-up air to enter around (hangar style) bay doors.

- Danger from flying objects/"being sucked into the hole." Not likely, as suction is a poor way to direct gas flow with significant velocity. Lots of designs must be put into hoods with significant airflow volumes to capture even vapors, so I'd have to put this near the bottom of the list. Keep people and their pens and pencils a few feet back and someone might have their hair mussed..
Tend to agree, based on "gut feel" alone, but I have nothing to support this feeling.

- Acoustic. The big one, and potentially nasty. There are lots of ways the glass could break, from an almost instantaneous total loss and implosion to a gradual degradation with slowly increasing opening size. Lot of things could happen here, from that very abrupt BANG! (could the glass be accelerated to faster than sound, could the inrushing air reach sonic velocity? I don't know, but I doubt it. <-- Not estimated or calculated, but 15 psi isn't much and most supersonic wind tunnels run at higher pressures)..
Agree that there are many failure modes, but I'm assuming the worst - nearly instantaneous, total failure.

Would it be "worth it" to get an expert's opinion? Maybe, but one would have to weigh the costs of that v. the probability of an accident. Where are you getting the glass? Could more than one layer be used? Is it shielded against objects falling on it? What are the total number of hours you would expect a person to be at risk over the lifetime of the experiment? If this is going to be a very long term study it may sway you to pay up to cover this base.

It's hard NOT to be very cautious, I know, but the budget has to be consulted. It's cheap enough to require hearing protection (I like to shoot recreation ally and use plugs and ANR 30 muffs together, they're very effective) but I suppose each situation is different.
Very astute. This is the decision process I must go through, and the reason why I created this thread in the first place. I needed further information before I could make a risk/benefit decision.

Ever thought of getting into the safety business?:)

[TillEulenspiegel]

jj perhaps I should have said an acoustical engineer then an acoustician. Mr Skinny I was indeed alluding to OSHA standards of allowable noise levels ( including accident risk assessment ) that are used for assembly lines, foundries , paper mills etc.

The fact is tho that we have focused on risk assessment rather then the constraints of Mr. Skinney's inquiry which is a financial question.

Theres one thing I don't quite understand, the window in question is used for passage of a laser, is there an instrument cluster or any other reason that would put an employee in proximity with the window? Are the processes controlled from a different point then the data collection of the process?

If so I believe that the ( let's call it a C and C station ) IS already remote and unless your using analog gauges with food grade SS wrapped cable and copper capillaries ( tell me your not ! ) the problem is one of extending the reach of the active signal network.The extension of CnC by wire would represent the cost of labor and signal carriers ( wire or optical fiber ) which is minimum in relation to the cost of a separate control room and would reduce the human risk as well ........drag the cabling over to the adjacent bay and You would probably solve both problems at once.
As an addendum, CCTY cameras are now less expensive then a pair of basketball shoes , you could set-up a few cameras to give remote access to the data at a very low cost, with no human involvement to boot. These could be used for gauges inside the vessel or as backup for outside, this could also offer documentation for the particular process undergoing testing.

I do CNC, instrumentation and remote sensing and control in my work ( don't laugh , but it's in the entertainment industry).

[ceptimus]

Cheaper than getting an expert opinion, and more accurate. Test it.

Fit an expendable window and break it by remote control without anyone present in the room. Record the sound level and any other effects using mics and camcorders.

If the inside of the vessel could be damaged by the splinters, you might want to fit a temporary liner, to catch them.

I don't know what will happen, but if I had to bet, I think the effects won't be that dramatic. If I had to choose between being close to that vacuum chamber, or close to a failing compressed air storage tank, I know which one I'd choose.

[Mr. Skinny]

Originally posted by TillEulenspiegel
jj perhaps I should have said an acoustical engineer then an acoustician. Mr Skinny I was indeed alluding to OSHA standards of allowable noise levels ( including accident risk assessment ) that are used for assembly lines, foundries , paper mills etc.

The fact is tho that we have focused on risk assessment rather then the constraints of Mr. Skinney's inquiry which is a financial question.

Theres one thing I don't quite understand, the window in question is used for passage of a laser, is there an instrument cluster or any other reason that would put an employee in proximity with the window? Are the processes controlled from a different point then the data collection of the process?

If so I believe that the ( let's call it a C and C station ) IS already remote and unless your using analog gauges with food grade SS wrapped cable and copper capillaries ( tell me your not ! ) the problem is one of extending the reach of the active signal network.The extension of CnC by wire would represent the cost of labor and signal carriers ( wire or optical fiber ) which is minimum in relation to the cost of a separate control room and would reduce the human risk as well ........drag the cabling over to the adjacent bay and You would probably solve both problems at once.
As an addendum, CCTY cameras are now less expensive then a pair of basketball shoes , you could set-up a few cameras to give remote access to the data at a very low cost, with no human involvement to boot. These could be used for gauges inside the vessel or as backup for outside, this could also offer documentation for the particular process undergoing testing.

I do CNC, instrumentation and remote sensing and control in my work ( don't laugh , but it's in the entertainment industry).
Till,

The basic idea was to fire the laser/collect the data from the catwalk in order to avoid running all the remote cables. I have already recommended to the project engineer that the firing/data collection be done remotely. Expensive, but cheaper than acoustic engineers, or, as ceptimus suggests, actually testing it.

We have a very nice control room about 30 ft away (horizontally) from the chamber, so we're only talking (30 + 27 = 57 ft) away.

And just to correct you a bit, financial considerations are a part of any risk assessment. It is part of the "severity" calculation which is inserted into the severity/probability matrix.

An old saying from my days as a fire protection engineer was: "Don't recommend a client spend $2 to protect $1 worth of property". I try to live by that "rule".

Anyhow, with the help of everyone here, I've come to a decision. Would love to be able to provide more detail (but then I'd have to kill you :D).

Too bad threads like this probably won't be allowed on here in the future. Wherever shall I go for my technical assistance?

[garys_2k]

Originally posted by Mr. Skinny

Originally posted by garys_2k

Very true. Here's my off the hat list:

- Injury from flying glass. Although much of it would implode into the chamber, some fragments would likely be expelled with force. Suggestion for protection would be safety goggles.

This is unlikely IMO. The probability of any pieces from a 4 inch diameter window exiting through that same hole after being sucked into a 20 x 27 foot chamber seems remote.

No, glass would not exit back from the port, I'm concerned about glass shards expelled from the outer surface of the port during an explosive failure. Cracks propogate at the speed of sound and small shards could be easily expelled from the outer surface with enough speed to escape the port's moments-later "suctioning." I'd expect to find glass at some significant distance from the chamber after such a failure.

BTW, if this whole discussion is off topic for the boards next month, I'll have to reconsider my sig. file.

[TillEulenspiegel]

Yes your quite correct, I just thought in the cost benefit analysis we were concentrating on the risk assessment and not a cost effective solution.

The thread was fun because it was novel, that's what I like about my work every new project is a one time custom project that presents different problems. It is a challenge and keeps the dust off the reference book shelf :)

Good luck on the project.

[Mr. Skinny]

Originally posted by garys_2k

No, glass would not exit back from the port, I'm concerned about glass shards expelled from the outer surface of the port during an explosive failure. Cracks propogate at the speed of sound and small shards could be easily expelled from the outer surface with enough speed to escape the port's moments-later "suctioning." I'd expect to find glass at some significant distance from the chamber after such a failure.

BTW, if this whole discussion is off topic for the boards next month, I'll have to reconsider my sig. file.
Don't know if I agree with you garys_2k. I'm trying to imagine a crack happening that would expel shards that wouldn't be sucked into the chamber microseconds later. Anyhow, it's moot point in this instance cause we require everyone to wear safety glasses in every laboratory, unless the lab supervisor has signed an exemption form saying they are not required, in their opinion.

[Mr. Skinny]

Originally posted by TillEulenspiegel
Yes your quite correct, I just thought in the cost benefit analysis we were concentrating on the risk assessment and not a cost effective solution.

The thread was fun because it was novel, that's what I like about my work every new project is a one time custom project that presents different problems. It is a challenge and keeps the dust off the reference book shelf :)

Good luck on the project.
Till,

Yeah, I had a lot of fun with this thread as well. One of the benefits of my job is working around a bunch of very smart people doing research, but who come to me saying "is it safe to do this?"

Usually, through experience and exploring reference material, I can find the answer, but this situation had me confused. I didn't feel I had a very good knowledge base for predicting what might happen in this situation, and I wanted to discuss it with some people with technical knowledge.

I wish I could post just a few of the weird one's I've handled over the years, but the gubmint frowns on me discussing my work on internet forums. ;)

[garys_2k]

Originally posted by Mr. Skinny

Don't know if I agree with you garys_2k. I'm trying to imagine a crack happening that would expel shards that wouldn't be sucked into the chamber microseconds later. Anyhow, it's moot point in this instance cause we require everyone to wear safety glasses in every laboratory, unless the lab supervisor has signed an exemption form saying they are not required, in their opinion.
No, a crack wouldn't expel a shard (I was unclear, I realize now), but an explosive break, "folding" the glass inward could cause the outside of the fold, toward the room, to undergo speed-of-sound disruption. Small bits of glass could be cleaved from the main masses at the break interface and expelled with force.