Looking for "Idiots Guide to ANSI"

[coolhand 0]

We had a bit of an accident last week on one of our Palletizers. The operator was reaching through a light curtain to fix a problem when he dislodged a part that was being held. The machine retracted to get another part and pinned him in the process. Fortunately he was not injured. This machine had light curtains installed 10 years ago and is simply sending a signal to the PLC. Unfortunately part of the logic was not there to prevent this from happening. Looking over the rest of the fleet of palletizers shows that this was the only one with a problem -but that does not mean it can't happen again. My remedy for that morning was to isolate the motors run command output with a Banner IMTA-9A safety relay. The relay is being powered by the Banner MUSC-1 light curtain controller via its FSD output. Now even if a light curtain is broke the signal to the drive is interrupted. Looking further at the literature for this relay and looking over the Light Curtain controller I still have a problem. The relay has four terminations labeled as Y1, Y2,Y3,Y4. These are supposed to be feed back to the Light Curtain controllers monitoring circuit. The MUSC-1 does not have an EDM circuit (external device monitor). After talking with the application engineers from Banner I will have to go about this "the way they did it in the old days". They speced that I use a force guided contactor with 2 NO/NC contact. This contactor will be mechanically linked with an add-on set of contacts to control the outputs to my drives. The Light Curtain controller will provide power to A1 and A2 for the coil (just like I had done originally) and the NC/NO contacts will allow power to the light curtain controller. -It's a bit confusing. They sent a pencil sketch of the basic idea of what will happen. It took awhile to find the needed hardware and I am still waiting for the stuff to arrive. We have been in the process of doing machine safety assessments and installing light curtains (modern ones) and other safety up-grades on door switches, etc. I do know that running a safety through a PLC is bad practice, but explaining that to Management and others has been difficult. Now that an accident has occurred for such a situation it will be easier to show the results. I have found that safety is not like running conduit and specing motor overloads. Doing Arc Flash is even easier. These all have charts and tables. Safety is a variable. Standards change, machines change, variables change. What I feel is safe can soon be disproved with -"did you think of this?", etc. Safety can cost a LOT of money. I would like to find a book/s like my NEC, or NFPA 79. Has anyone written a book for the tech to help understand what is needed in a safety control circuit, how to do a proper assessment, what installation standards are needed....? If it were only one machine with this problem I would be inclined to spec a newer light curtain controller for this spot. Unfortunately the plant has ~40 of these "legacy" controllers. We also have sister plants that will be following our example as well. Any thoughts, comments or suggestions are welcome. Thanks Luke

[Chris Elston 78]

Luke, On of the places I looked when I was first learning was an STI catalog. Or now should be the Allen Bradley Guard Master catalog. The entire front section was dedicated to applications, and of course "their" product recommendation to solve the safety problem. They also have a risk assement forms you can wizard yourself through and come up with a category rating your shooting for in your safety circuit. Start with the risk assement first, get a category number, then design your circuit per what ever your risk assement is for. I wish I has an STI catalog in PDF format, I would upload it for you. EDIT: I mean Omron Catalog....Omron bought out STI.

[BobLfoot 301]

Chako's advice is solid. Get a guide which will help you thru the Risk Assessment portion. Try the STI site {now managed by Omron} or the AB/Rockwell site or possibly OSHA.GOV for risk assessment tools. The NFPALearn.Org site is another good one. Once and only once you know your risk, can you truly design a code compliant system. Personal Opinion Follows: Given you have "legacy" equipment, I personally would check out the Rockwell Safety Rated PLC's. This might allow you to add safety and upgrade your Palletizer controls in step. The Safety Portion of the PLC is redundant and "fails to a safe condition". It also supports devicenet limits and pushbuttons so the install is simple. yes we use a lot of AB and I have a prejudice in that direction.

[coolhand 0]

Thanks for the replies. I have a few of the safety catalogs and it may be time to go back and read through them again. One of the things you hear at any company is “Safety First”. That sounds great until you try and drum the troops together for support. To me it seems odd that my boss and all the bosses up to the plant manager and even the president of the division are leaving a critical solution to a maintenance guy in the trench. –Sure I have gained the respect along the way, but it would be nice if there were some others within the division to lean on. I’m afraid that I’ll end up being the go-to guy for solutions and don’t want an incident to occur ten years from now with my name attached to it. I guess it’s a bit of a vent for me. I was not aware of the NFPA site and will have to give it a perusal. I have read only a little on the safety rated PLCs. I am curious how they work, or how they “fail in a safe” condition. I’ve been installing new light curtains, muting modules and safety relays at the palletizers exits. The only thing I take to the PLC is an input halting the logic. I have various drives I have been inhibiting from getting a run condition by controlling the drives common threw the safety relay. Every module is checked by the one it’s connected to for functionality- i.e. redundant. What would be nice for a system like this is “patch cables” to go from one device to the next. I’ll be I made ~50 terminations for each one of these exits. If I were to have done this with a safety PLC what would eliminate the human error of programming? Having hard wired like my explanation above, even if my program in the processor got changed the drives will still not be able to run. As for risk assessments- when you perform them who does them with you? We did them a few years ago for this same palletizer with my boss, a couple of other maintenance techs (they used to run these lines as well), and my-self. Not being aware of all the regulations a lot was left to speculation. Last week we had a guy get his arm caught in an un-guarded area and the week before the incident with the old light curtain. Both of these were never considered on the initial assessment. It’s hard to see every thing that can go wrong or anticipate where a new hire might stick an arm. I am amazed at how many people I see working around machines with no thought about the dangers that are present. There does not seem to be an age limit to this observation. Much like people driving cars I guess. I’ll give my catalogs another read. It would be nice to have a good book like the NEC written for the layman- this way the decision makers could see why things have to be done a certain way. You know what I mean. Luke

[rpraveenkum 5]

you can get all safety related details here http://www.ab.com/safety/prod_directory/index.html have alook on these http://www.ab.com/safety/library/index.html

[Ken Moore 23]

My back ground is mostly process controls and only a little machine control. But I think the way we handle safety may be applicable. We do something called a hazard assessment, this is done by a team of people. The team must have at a minimum, 1 safety professional (knowledgeable in applicable regulations etc...), 1 operator, 1 maintenance person, 1 engineer, 1 operations management person. We do a what if type scenario on every piece of equipment in the system, what happens if this PE fails, what happens if the push button gets stuck, what happens if the maint. guy wires the motor in reverse, etc.... You really must have the operators and maintenance people involved. Many times the engineers and the managers think something is done one way, but on the floor, the operators actually do something completely different. Once you have identified all the potential hazards, you can then start to apply engineering controls (light curtains, safety relays etc....) and written procedures to reduce the risk. As for safety PLC's, don't have any experience, but I do have SIL rated PLC systems that are used for emergency shut downs. We follow the ISA standard for these, S84. There may be a standard for machine safety as well, might want to take a look at the ISA website: www.isa.org The S84 standard requires that a competent person write the plc code, and then it must be reviewed by a second competent person. Once the system is commissioned, any changes require a written approval process, you can't just go on line and make a change. You have to document what you are changing, why, and the expected results. Then a review team determines if the change is warranted, and upon approval, you must make the change, test it, and then get another person to verify your changes and testing, it's a lot of paper trail stuff, mostly to protect your back side. With all the reviews and such, you are less likely to miss a critical issue, and since there are multiply people involved, you can all hang together if something goes wrong. Hope this helped, but it was kind of rambling I must admit.

[paulengr 44]

Mike Holt does some excellent training books with regards to the NEC and a FEW of the associated materials. It is not a safety training program in general. Part of Dupont's program is also called "STOP" which is an extremely general program. It's sort of a "foundation" system for all the others. I have personally seen it implemented in one plant where in a single year, accidents went from 140/year to 80/year, and LTA's went from 14 to 8. In another plant in a single year, TCIR went from 8 to 6. It is VERY simple to comprehend and use, and geared towards hourly employees and front line supervisors. Edited 22 Jun 2007 by paulengr

[GerryM 2]

As far as OSHA goes this is the one phrase that I tend to work by: " The point of operation of machines whose operation exposes an employee to injury, shall be guarded. The guarding device shall be in conformity with any appropriate standards therefor, or, in the absence of applicable specific standards, shall be so designed and constructed as to prevent the operator from having any part of his body in the danger zone during the operating cycle." here's the link to it: OSHA As far as ANSI goes they have some spec.'s for specific types of machines in the ANSI B11 series. ANSI B11.19 conatains general safeguarding principles, and ANSIB11.TR3 has recommendations for risk assessments. Other than that I also like STI's website and products: STI's Safety Corner Your local safety supplier or control integrator may also be able to help you with safety assessments.

[coolhand 0]

Thank you very much for all the responses. Thank you also for the links -some good sites and some very good insight and info. I'll be referring back to this info a few more times J One thing I have realized through this whole process is that an assessment can be a bit ambiguous and not always clear cut. If I were safeguarding a punch press for instance, there are definite standards on how this is to be done and how the operator is to work with it –anti tie downs, etc. Now after an assessment is completed for a certain area, a solution has to be made. Hardware is purchased; and integration of that solution begins. One company I have dealt with has some very helpful application engineers and has not tried to over sell their goods to us. In integrating one solution I had some troubles with shutting down AB servos and after talking with AB, they want to sell me more hardware stating that it needs it to meet a cat. 4. I guess what I am finding is that I have to educate myself to ask the right question, and not to always trust the application engineer or phone support. Fortunately for me, we had a corporate Health and Safety manager in the plant last week. Since we are a small division of a large company, I asked if there were folks at corporate who would be able to assist in answering questions. I called the first name and found that they had already assembled a team for light curtains and machine safety on some similar equipment. I also found that a recently acquired plant that is similar to ours has done quite a bit of this already. It's kind of amazing that I would ask my boss and the plant engineering manager and get no help in tracking down a contact person within the corporate realm. Oh well. Thanks again for your time in responding. Luke Edited 29 Jun 2007 by coolhand