a question about machine guarding

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billk554

Member
the place i work is putting prox switches in for safety switches. when the guard cover closes the prox allows the machine to start. also when the gurad is opened during opperation the machine stops. they work o k but are easily defeatable. i was under the impression that a positive contact switch needed to be used. somthing with a key like device that fits into the switch body. am i wrong? the machines we are talking about are printing presses on a paper bag line. we make paper bags. my boss(a mechanical engineer) feels these are o k. i think we need to use somthing different. can anyone quote the passage in the standards about safety switches on machinery?
 

Billy_Bob

Senior Member
Location
Oregon
I read your post and was thinking... Where on earth (among all the agencies, rules, and laws on this stuff) would someone look to find such information?

Well I searched google.com for the words

osha guard switch

And found a treasure trove article which lists specific rules on this by agency and code number! (Your lucky day!)

Note the article says 1996, so check for newer rules/laws.

Here is the article...
http://www.schmersalusa.com/catalog_pdfs/movable.pdf


FYI - The various rules listed...
(From 1996 article)
-OSHA 29 CFR 1910.211: Machinery and Machine Guarding
-OSHA 3067-1992 (Revised): Concepts and Techniques of Machine Safeguarding
-ANSI B11.19-1990: Safeguarding Reference for B11 Machine Tool Safety Standards
-ANSI B11.20-1991: Safety Requirements for construction, care, and use of machine tool manufacturing systems/cells
-ANSI-RIA 15.06-1992: Safety Requirements for Industrial Robots and Robot Systems
-European Machinery Safety Directive (EMD) 89/392/EEC
-UL491 (Proposed): Power Operated Machine Controls & Systems
 

billsnuff

Senior Member
You need to get a copy of ANSI B65.1-2005 Graphic Technology - Safety Standard - Printing Press Systems and read section 17. Also, 1910.147 (29 CFR)

There are tasks on a press (repetitive) that do not require LOTO as long as proper documentation and training has been done. That said, guard with safety switches are considered 'enhanced safety devices' but do not constitute LOTO, because guards need to be secured in place by a unique fastener and you cannot use 'control circuits' for LOTO.

29 CFR 1910.211 and ANSI B65.1 - 2005 also cover guarding.
 

drbond24

Senior Member
the place i work is putting prox switches in for safety switches. when the guard cover closes the prox allows the machine to start. also when the gurad is opened during opperation the machine stops. they work o k but are easily defeatable. i was under the impression that a positive contact switch needed to be used. somthing with a key like device that fits into the switch body. am i wrong? the machines we are talking about are printing presses on a paper bag line. we make paper bags. my boss(a mechanical engineer) feels these are o k. i think we need to use somthing different. can anyone quote the passage in the standards about safety switches on machinery?

Whether they are easily defeatable or almost impossible, if someone wants to get around them they will. Unfortunately, you cannot make it idiot proof. You have to convince the idiots that they like having their limbs attached where they are and if they want to keep it that way they should use the safety devices you provide.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The big thing is that it depends on whether you are using the switch to protect human beings from danger or merely as a means of preventing the machine from running while the guard is open.

If it is to protect the human being, I would be very skeptical of the use of a standard prox switch. If it is to protect the machine, its OK.

Keep in mind most guards are removable and very few have switches on them.
 

VinceS

Senior Member
Check out NFPA 79

Check out NFPA 79

NFPA 79 good standard to follow.

I don't think anyone mentioned OMRON safety website: http://www.sti.com/index.htm

Tons of good downloads on the Omron site. Register and they will followup with phone call and email. They are trying to sell stuff after all...
 

VinceS

Senior Member
If you call it safety, you must monitor it.

If you call it safety, you must monitor it.

If your sensors are being used for personal safety devices they will require new and special devices rated for personal safety. Oh they have a much higher cost, due to built in redundancy and self failure monitoring.

I can't quote you chapter and verse on this its well beyond the NEC. As with most safety installs you may wish to consult with your companies Safety or EE to approve your design. You may even wish to outsource this for liability issues.
 

billk554

Member
thanks for all your reply's. the gurading is definitly used for protection of life and limb. we have had several injuries with loss of finger/ hand parts. the gurads are to stop this type of accident. these were quite recent injuries. (with in the last year) the message went out to guard the machines so this would stop. i have seen the safety switches with a key like interlock and recomended them but to no avail. prox switches were installed and are still being installed. there is a set up procedure where as the machine is alowed to jog during specific times of the set up process but not after that. there is a set up switch on the machines to do this. i am worried about the prox switches and that they are not the best fit for this application. again thanks for your time. this sight is a great resource.
 

mxslick

Senior Member
Location
SE Idaho
<snip>.....there is a set up procedure where as the machine is alowed to jog during specific times of the set up process but not after that. there is a set up switch on the machines to do this. i am worried about the prox switches and that they are not the best fit for this application. again thanks for your time. this sight is a great resource.
(Bold added by me)

Would that process be the loading of the printing plates?

I see what the switches are trying to accomplish, but as said already, someone WILL figure out how to defeat any safety switch you may choose to install.

I think prox switches, although not the best or maybe even rated as "life safety" switches, are the best for the job, as they are immune to a large degree from dirt, oil and other contaminates affecting their operation.

The best thing you can advocate for this situation is better operator training, with quarterly refreshers on the dangers of the machinery. :)
 

billsnuff

Senior Member
you may want to check out these products..............

http://www.ab.com/catalogs/safety/index_prodtype.html

and get you self a copy of the ANSI B65-1

http://webstore.ansi.org/RecordDetail.aspx?sku=ANSI+B65.1-2005

I have been in the printing industry since '69 (yeah, i'm older than dirt)

then get to know the lock out rules

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9804&p_table=STANDARDS

then do a risk analysis for each procedure to see what level of protection is necessary, this is where you get the buy-in from the boss........

http://archives1.iomosaic.com/whitepapers/risk-ranking.pdf
 

charlietuna

Senior Member
Most machines have safety ratings with the design to protect both the operator and surrounding personel. Even a key switch can be defeated by the operator! In the printing industry there are many interlocks on machines that protect the operator that are easily bypassed . It seems to me that - the more common the accident - the more severe the interlock is designed to bypass--but they can all be bypassed. Consider the design of the interlocks on a paper cutter compared to the door interlock on the delivery end of a press?
 

aja21

Member
Location
Nebraska
I agree with all of the statements made on this thread but I think that the particular switch you are looking for is called a trojan switch (brand name?). We used these everywhere in the plant I worked in when it was obtaining OSHA VPP star site status. Problem is I cannot tell you the OSHA rule that requires them or if it does "require" them. It sure did bring down the amputation #s.
Another thing that would help is a two handed jog ckt. using palm buttons requiring both hands. These can still be defeated but the stance that the co. took on this was if you defeated this you worked pretty hard to do so and the co. was not liable for your injury.
 

pfalcon

Senior Member
Location
Indiana
One of the early posts has good references to the safety device requirements. Your application definitely requires them. In order of preference I would suggest:

1) Turn this over to the responsible engineer to design. Let management know that they are the ones going to jail and losing their houses when the next guy gets hurt and takes them to court. The courts sometimes call the managers to account when there is an injury history.

2) Install safety rated devices on this application. Do NOT skimp by installing regular prox switches. This application also requires safety relays and proper tie-in to the Estop or other safety circuit. You should be nervous about doing this right. You stand to lose a great deal if someone gets hurt afterwards.

3) Get written orders if they insist you install something less than safety rated devices on a safety circuit. This should also stand to warn them if they can take a hint.

This isn't residential wiring so the likelihood of getting caught by OSHA or another organization is often much lower but with much higher penalties when you do get caught. The lack of guarding or use of regular proxes are definitely violations.
 
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