Fatal Incident - Safe Isolation failure?

Depends on the sort of servicing - maybe he was not an electrical type , but sent to check the oil levels or change a belt.  I agree there might have been holes in his training or shortcuts taken in the process used, but we do not know the full story, and should probably not speculate too wildly.

Sad news whatever, and I would say really very unlucky in any case - there are far more shocks that lead to a lot of swearing and count as near misses than deaths.

mike

yes - Fair points.

I've certainly received more than one ‘swear-inducing’ mains voltage shocks in my past - more so when I was younger and more stupid than I am now….

I actually think that the “Safe isolation procedure” taught to us is flawed, it is fine on a healthy circuit or installation, but on a faulty circuit or installation it does not work.

A test lamp will only light if there is a voltage difference, if as I have done you find an installation where there is mains voltage on the earthing system the test lamp will not light when placed between live and earth as they are both at mains voltage. indeed the first thought you may have is that there is reversed polarity rather than a major earth fault after testing the neutral as well.

AFAIK, the number of workers electrocuted at work sits stubbornly at around 20/year in UK.

“The engineer of 30 years believed power had been cut to the machine. But, a fault meant a metal plate was permanently live at 240 volts, leaving him exposed to a deadly quantity of electricity.”

Single pole isolator in the neutral? Reversed polarity and single pole isolator?

I would like to think that an experienced electrician would prove dead. As Mike points out, the work might not have been electrical as such. Perhaps checking the pressure switch?

This one is also unforgivable. https://www.bbc.co.uk/news/uk-wales-57810059

I actually think that the “Safe isolation procedure” taught to us is flawed

I tend to agree. Even with the test-for-live, isolate, test-for-dead procedure it's possible for the wrong thing to be isolated but the test-for-dead still to show dead as the machine has been halted, coincidentally, by some other mechanism - say a thermostat or perhaps in this case a pressure switch - only for the power to then return, automatically as it were, some time later while maintenance is still on-going.

Hard to see an easy solution to that kind of situation, but worth keeping in mind all the same.

Borrowed neutrals add another layer of danger - as they can test ‘dead’ but turn live as soon as they're disconnected.

   - Andy.

Sparkingchip: 
 

 

I actually think that the “Safe isolation procedure” taught to us is flawed, it is fine on a healthy circuit or installation, but on a faulty circuit or installation it does not work.

A test lamp will only light if there is a voltage difference, if as I have done you find an installation where there is mains voltage of the earthing system the test lamp will not light when placed between live and earth as they are both at mains voltage. indeed the first thought you may have is that there is reversed polarity rather than a major earth fault after testing the neutral as well.

Voltstick.

Z.

The other approach is to teach every one to work as if  live working all the time, and avoid two hand contact as much as possible, and to connect things with metal before straddling them with the body.  I do recall about 20, no 25,  years ago replacing a light fitting in someones hallway with the fuse in my back pocket, as was typical ‘lock off’ for the fuse-boards of the time. I was both very disappointed and in another way pleasantly surprised when it was all done and I put the bulb into the holder and it came on !! By some remarkable luck, I had neither blown the fuse to the circuit it was actually on, nor given myself a shock. 

I had the doubtful advantage of experience in my dad's workshop where valved things running  with the lids off were quite  normal, and the HT soon taught you not to prod things, and the wisdom of keeping at least one, or ideally two hands behind your back when not required was drilled in at an early age.

If you make things too safe, everyone assumes it is always the case and may become careless.

This does not help the victim in this case, and it may well have been a double fault, such as CPC off and also an insulation fault to case .

Mike

There’s a really good video on YouTube which I think is on the IET channel, but I cannot find it.

A TNCS installation is proved dead with the main switch off, but there’s diverted current running through the earthing system, even with the main switch off as soon as the main earth is disconnected everything that is earthed within the installation becomes live. The conclusion is that the current Safe Isolation Procedure is not fit for purpose, the main earth conductor needs checking with a clamp meter for current.

So it’s not only me that think the current procedure isn’t fit for purpose.

No such thing as Safe Isolation.

Firstly a lot of 2 pole testers need a potential difference between the poles to detect anything? If you have a live conductor or terminal and no earth or neutral a 2 pole tester will not detect anything. Some 2 pole testers will give you a one pole warning but not all.

Secondly testing only may prove dead at the time of testing micro seconds later a terminal may become live through a borrowed neutral, another supply not known about or someone doing something daft like breaking off your padlock.

At all times treat everything as live including anything coloured green/yellow.

I agree with Zoom get a voltstick. Preferably the Kewtecch Duo with the dual sensitivity. Keep it in the top of your shirt at all times and use it before you poke your digit(s) in to anything electrical. Yes you can get cheaper voltsticks but they are probably crap and what price your life.

If the poor man had used a voltsick then he would still be alive.

mapj1: 
I do recall about 20, no 25,  years ago replacing a light fitting in someones hallway with the fuse in my back pocket, as was typical ‘lock off’ for the fuse-boards of the time. 

Perhaps not strictly orthodox, but fuse in back pocket, as opposed to key in back pocket is good enough for me.

At my self-build chum's house, the fuse from the switch fuse which supplies the house is in my pocket. I accept that somebody could come along with a BS88-3 fuse and re-energise, but only maliciously.

Similarly, most of the dolly locks which one sees can be removed with a sharp tug; that is if they have not already fallen off.