Before the days of OSHA LOTO rules and devices we had safety interlocks. This, of course didn't stop anyone from disabling them. But anyone responsible for safety of personnel or of themselves would test interlocks to see if they were still functioning as intended.
Too many broadcast engineers were electocuted by transmitters turned back on remotely by studio personnel while the engineer was inside the cabinet at the remote mountain top tower site! Has anyone seen Paul? And why are we off the air this morning?
Always working with a buddy rather than working alone in the middle of the night is the right precaution but is all to often not made available to personnel due to budgetary constraints.
Never trust interlocks to work. Besides you don't want to come in contact with live primary power rails even if the HV supplies are interlocked off. I always pulled the fuses or disconnects and then tested with a voltmeter to be sure all input power terminals were cold. Never send someone else to do the LOTO. Witness it yourself to be sure it was done right.
I knew of a semi retired older broadcast engineer who did a small station owner a favor and came by to repair his AM transmitter. He asked the owner to throw the main circuit breaker off. Turned out the breaker panel had been illegally set up with single pole breakers, rather than double pole interlocked for the 230 VAC feed to the transmitter. The helper flipped one breaker handle off. The old engineer happened to touch the remaining hot leg (120VAC) getting a stiff surprise. He had never before gotten a significant electric shock. He sat down and turned pale. When he recovered he left, vowing to never come back and to make his retirement perminent.
Some transmitters do not have "Jesus sticks" aptly named grounding devices that when applied to charged terminals can create quite a loud blinding flash. Besides locking out energizable circuits, grounding the heck out of anything you may be working on is another good precaution.
I once had some work to do on a brand new NEC (made in Japan) UHF TV transmitter. Klystron tube beam current power supply voltage was in the 30 kV range. The schematic diagrams showed interlock switches guarding every access door and panel to the transmitter. But on further examination I noticed the switches were wired to TTL logic chips in the controller! Should one trust their safety on TTL logic? Of course not. Proper design would require the interlock switch to directly open the circuit to a main contactor coil or its pilot relay thus preventing startup. TTL logic could easily become noisy, leaky or shorted, thus rendering the interlock useless.
I left out the 'Try' component in my earlier post, but that was a required component of the process. Verify that the equipment cannot not be energized after the locks are in place and before a permit is issued to work on the system in question.
And with regard to another posting about an employee leaving the site without removing his/her lock - I know of a case where an employee did just that. The mill contacted the employee and required him (in this case) to return to the site to remove the lock. The time was unpaid. To make this stick, you have to have a committed company safe work culture, and other parties(unions, vendors) have to be committed as well. It should make sense to the union guys. Who wants to go home missing a limb or in a pine box at the end of the day? For vendors and contractors, you make the expectations clear, hold them to those expections, AND ask them to make it known if it seems that anyone else at the site is not meeting those same expectations. The principle is that nothing we do is worth the cost of an injury.
YES! Lock-out and Tag-out (LOTO) is one of the basic fundamental safety needs when operating in an industrial maintenance environment.
I have annual LOTO training in every job I have had with access to industrial equipment. This has included being issued my own set of locks. Each person with hands in the action had their own locks on the lock out. I would fully expect termination from unauthorized removal of a lock. Unauthorized means removing any lock except your own. One cautious exception: If you forgot to remove your lock from one of the energy sources, or the work was finished on a different shift, your supervisor or the safety director COULD talk to you directly, or by phone, to CONFIRM that you were done in the machine, AND with that same supervisor sign-off taking personal responsibility. (In my 32 years in industry, I have never personally known this to happen. I have known supervisors to call an employee back-in to remove his own lock on two separate occasions with different employees.)
When I worked at Dupont they instituted a Lock, Tag, and Try procedure. This required a LOTO AND an attempt to start the equipment to verifiy that lock-out was effective, in case, circuits were mislabeled before lock-out. Inproper lock-out can frequently be a likely risk of death or serious injury. I only knew of one case when this too failed, when tank stirrers were on an automatic timer tied to processing and were mislabeled. I was not close to this incident, but I understand it led to 2 deaths. Very sad, but it shows how important this is.
From my experience, Dupont had strong safety policy tied to the company's explosives manufacturing history with owner family-members business-related explosion deaths. This safety focus was reinforced in current times for management support, by immediate plant manager termination if there was a death in his plant! Plant managers would therefore error on the side of being overly focused on safety. (Certainly, the better way to err.) If a major safety procedure was violated, that was also grounds for immediate termination.
The only commonly prepared-for safety-related items that seem as extreme to me as LOTO would be firefighting "BLEVE" explosion, fire "flashover", and high-voltage "arc-flash" hazards being underestimated.
Double lockout is one option, it was not available in the one area since it was where the machines were being built. My solution was to lock out the disconnect switch, remove the fuses, and tie the three phases togather downstream of the switch. This combination was enough to prevent the monkys from being able to switch on the power without going to more effort than they were willing to expend. And the short circuit insured that they would be noticed, and I would be able to move clear, before anything could start. Yes, it was extreme, but it worked well. PLUS, I did not need any training to figure it out.
At that time I was not aware of proper LOTO. The co. I worked was (and still is) a major chemical pump mfg and sells both domestically and internationally. It should have been mgmt's responsibility to know of and provide proper training. The co. I worked for before this one, I traveled and performed product start up, maintencance, and training as well for 7yrs. That co. also did not train me on LOTO proceedures. I will admit that I was ingnorant of proper regulations, until after this occurance. Even afterwards, LOTO training was not provided. And believe me, when you are working at various plants and start using your own lock, you do hear people in charge of production "complain" (with a capitol "B"). That is whay I included my contact infomation as well as dept I was working in, and dept mgr's contact as well, on my tag.
Once again, excellent postings and you are correct. It was my error through ignorance as well as that of my co's and the co. that I was working at.
And neither was the maintenance man that assisted me. He was screaming how was it unlocked without cutting it off, as he had the key in his pocket? (As the lock was once again hanging on the wall.) It was then that we found out that they had previously experianced issues with someone locking out and then leaving when their shift was done, taking the keys home with them. the next crew would finalize the repairs, but equipement still could not be turned on. Then came the issue on who was holding and controlling the duplicates. We were advised it was the foreman, who was unavailable at that time. The maintenance man filed a grevience with the Union before I left. I did not pursue this any further, although I could (and probably should have) called OSHA. In reality, if you make too much of a stink at a facility doing a lot of business with your co. and you lose them a huge sum of $, your chances for survival in that position are greatly diminished. Right or wrong, that is reality. In this case I had a family to support. I could push the issue, and 3 month later be replaced. I did advise my mgmt, but with no injury, those pencil pushers brushed it off. Even though I was the lead tech, lose a co. enough $, and something will hit the fan.
Water.ratz and Fred are correct, and Rob Horton should NOT have been doing this work without getting and following the required OSHA training. Lockout padlocks must have one key controlled by the worker, not a lock that anyone else has a key to. I'm doing a LOTO training refesher later today, and each of my employees has a one-key padlock and set of tags. The root cause here is that the worker did not use his personal padlock, secondary is the monkey that removed the lock that was in place, third is the company's attitude that production is the first priority.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.