Vacuum Chamber (potential safety issue)

[jj]

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]

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]

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]

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]

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]

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]

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 ).

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 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]

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]

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]

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.