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Audible alarm interlocks????

Posted: Wed Apr 17, 2019 9:59 am
by Keith1983
I've come across a situation today whereby a piece of equipment has an interlocked gate fitted to prevent access to dangerous moving parts. So far so good. I have discovered also that the interlock does not power down the machine but sounds an audible alarm. This isn't something I've come across before. My gut feeling is that its pointless as it doesn't stop someone accessing moving parts, it just makes an annoying noise whilst they do it? What's people's thoughts on this???

Re: Audible alarm interlocks????

Posted: Wed Apr 17, 2019 10:52 am
by PaulDonaldson
I thought the whole point of the interlock was that if the interlock is open there is no power to the machine?

Re: Audible alarm interlocks????

Posted: Wed Apr 17, 2019 10:56 am
by Keith1983
My thoughts exactly Paul! I'm a bit baffled by how we came to that situation in the first place. Is it something you've come across before?

Re: Audible alarm interlocks????

Posted: Wed Apr 17, 2019 11:22 am
by bernicarey
Simple answer is that what you have there is NOT an interlock.

It does not prevent an action being performed.
There's a good description on Wikipedia about engineering interlocks (as opposed to other sorts like, err...knitting stitches ;) )

It includes this comparison....
Although both are idiot proof strategies, an interlock should not be confused with a simple safety switch. For example, in a typical household microwave oven, the switch that disables the magnetron if the door is opened is not an interlock. Rather, it would be considered an interlock if the door were locked while the magnetron is on, and the magnetron were prevented from operating while the door is open.
What you have does not even compare with the microwave door catch :shock:

Re: Audible alarm interlocks????

Posted: Wed Apr 17, 2019 11:30 am
by Keith1983
That's a brilliant analogy. Thanks Berni. I'm puling a team of relevant people together this afternoon to discuss the issue and also carrying out a walk around of the factory to identify if we have the same situation anywhere else.

Re: Audible alarm interlocks????

Posted: Thu Apr 18, 2019 9:43 pm
by Jack Kane
I've been having a few conversations recently about the difference between interlocks, engineering controls, procedures, processes etc. Some quite interesting views on things.

For example, I've asked for an engineering control to stop an hazardous activity in a couple of ways. One is by an interlocked gate/door/hatch whereby the hazardous work will stop immediately to a safe state if opened, or will prevent the work starting in the first place until the system is reset. The other being an emergency button or pull cord to stop to a safe state. Again, a reset required after activation.

The alternative offered to me is a great idea and will work to a point, nothing wrong with the thought process, it's just the understanding of what an engineering control actually is. The idea is to attach a padlock to the access door to the control room, remove the master key from the control panel and attach signage to the control room.

The thinking is that once the padlock is attached and the other key is removed, in order to reactivate the system somebody will need to physically remove the padlock and engage the master key again. After all, the controls won't work if they can't be accessed or switched on without a key. The flaw here is that it all starts with a process. The process of attaching the padlock and removing the master key. Reliance on the human being and their pesky behaviours to follow the first process.

I just don't like relying on humans, we're just too unpredictable!