Hi, We received a report recently regarding an incident in which an electrican suffered severe burns to the face, arms and legs, while working on an electrical switchboard on a vessel when an arc flash occurred. This was not something I was previously very familiar with. However, having spoken to my counterparts in the US, it apperas they are considerably further ahead in addressing this hazard. They bought a software package that allows you to conduct arc flash analysis and risk assessment accross your entire electrical system and then develop safe boundary levels and select appropriate PPE to afford some pretection against the intense heat and projectiles that can be generated. Our electrical maintenance engineer doesn't think this happens very often in the UK, and ther certainly doesn't appear to be much UK based information on the subject, but a considerable amount of US based info. Does anyone have any information about arc flash ocurring in the UK - frequency, examples, approaches taken to manage the risk, relevant bodies that can advise etc? Regards, Richard

Hi Paul, Thanks for your reply. I'm not convinced that the lower frequency of arc flash in the UK is due to better working conditions than in the US. The variables that affect the generation of an arc flash include: The speed of any overcurrent protective devices Arc gap spacing The size of the enclosure or absence of an enclosure The power factor of the fault The system voltage Whether an arcing fault can sustain itself The type of system grounding and bonding present I'm not sure that these factors are adressed to any lesser degree in the US than in the UK. In an arc fault the air becomes the conductor, and the fault itself is caused by a conductive path or a failure such as broken insulation. I'm curious to know if the climate has anything to do with it, e.g greater humidity leading to a more conductive atmosphere. In terms of the electrician in question, a root cause analysis is underway, and yes I believe he was working live - the details as to why have not yet been made available. He was working on a US vessel off the coast of the US so the EAWR 89 do not apply, though to say that live working is against the EAWR is not strictly true for the reasons outlined in Reg 14 - fault finding, testing etc. as you've noted. My query relates not so much to this incident in particular, but more towards trying to establish whether arc flash is known to occur in the UK, and any examples of this. If not, have the reasons for this been researched? Regards, Richard

From the HSE web site - an incident as recently as September... "... One of the workers ... received severe burns to his face and hands, needed three months off work to recover, and required treatment to remove debris from his eyes. ... an investigation found electrical work had been allowed to go ahead without the power being cut. ... replacing a temporary generator for the landing stage at the ferry terminal with a supply from the mains. ... the work had gone ahead while electricity was still running through the switchboard. When one of the workers tried to install the new fuse, there was a bright flash and an intense heat caused by a fire, lasting just a few seconds. ... glasses were badly charred in the flash fire and he needed four days in hospital after suffering severe burns. The other worker ... also received burns to his face and required hospital treatment. Both workers have asked not to be named."

RHOES/Richard, I fully understand the mechanisms and requirements for Arc Flash. However, there is one way of eliminating the possibility of this no matter what the other conditions you list are. De-energise and suitably earth down all conductors in the proximity before undertaking any work! ;) If the system is correctly isolated and earthed as appropriate then no arc flash can occur. You will find that a correctly designed, installed and maintained, low voltage electrical distribution system in the UK will clear a fault with a current level sufficient to sustain an arc flash in around 0.1s. This is probably another factor to consider. Remember also in the UK that there is little HV work done by electrical contractors, almost all electrical contractors unless specialists are restricted to low voltage in the UK. Was this HV or LV work being undertaken, was it 50, 60 or perhaps 400Hz or another frequency? Was it d.c.? I also do believe that our systems are inherently safer than those in the US, that BS7671 & IEC 60439 & other associated standards do provide for better protection then the NEC, I feel that the NEC tries to cover too much in one document. As Steve has posted there are arc flash injuries in the UK, most are related to live working incidents which should not happen, especially on HV lines such as the last Dec 11 incident listed above. Again IMHO and that of "my" local head of electrical at HSE, along with many other electricians I meet and electrical engineers that I discuss this with, they do not class live testing and fault finding as live working. If you look at the lists of examples given by "steve e" above then one thing appears common, live WORKING, not testing or fault finding. Again all IMHO, but then I do this for a living & I'm still here!

JohnM, Whilst your point is valid, I feel we need to draw some lines between certain activities. IIRC if you check EAWR, then it is also illegal to work in proximity to energised conductors. The utility companies are a different kettle of fish. In your scenario they are not undertaking live working as an electrician would be. I am not diminishing the possibility of injury, nor the severity, nor it's impact on the IP and their family & friends. However, there should be no cases of arc flash in this scenario on low voltage systems. In the UK the work on high voltage systems is restricted to the DNO's, NG & their "authorised" contractors outside private HV distribution systems, which the insurers of which will insist on their own SSoW SAP's etc.

I have personal experience of two flashover incidents on a three phase main in the last ten years. One was while an electrician was working on it, and it caused injuries that kept him away from work for five weeks. The other seemed to be spontaneous breakdown in a distribution board. No-one was close to it at the time. The resulting arc completely vapourised a chunk of the centre conductor and gouged a large area out of the other two. Only one of the fuses (several hundred amp fuses) blew.

The problem was inside the distribution board, and the arcing was between the main bus bars. As I said, one of them had a large chunk completely vapourised in the incident - this left it with a gap. The other two were partially vapourised. It was maintained and inspected to the normal schedule. The cause of the flashover was never fully established, but there were some 'tracks' down the resin bonded insulator elsewhere in the same box, along with some droplets of copper, so it appears that the insulation could have failed. It is possible that something conductive had draped itself across the conductors, but it would have been vapourised in the flashover, so we will never know. Luckily no-one was very close when it went up. Luckily someone was quick off the mark to put out the fire and to throw the switch on it.

We must also consider the fact that the person was working on a vessel [ship/rig etc?] at sea and the work could of been under masters orders as a normal part of ship operations as against a separate area where certain controls are, because of sea going ship needs, more flexiable

psyco, Having a "floating" N is no different to "within" a fixed install in the UK, the N is still a live conductor. One has to be careful where the distinction is drawn and the exact system. There would be no reason to tie the N to the hull anyway. There are also a lot of fault monitoring systems as I understand things, well at least on reputable vessels. I have deliberately stayed away from the vessel reference for a few reasons: 1. I don't have a copy of the relevant standards. 2. I have not worked to these standards. 3. I am not familiar enough with ship board wiring. 4. The OP asked about installs "IN" the UK, which I took to mean land based. 5. It was IMHO the OP that moved the question shore side as it were. However, bob, & psyco, may well be correct in that as this was a vessel at sea, oh, and in the US, there is doubtless other pressing issues! I have tried to draw the line between LV & HV supplies in the UK, some supplies shipboard may be HV, however, in the UK, HV working is quite controlled on shore as it were. It is only LV stuff that is open to all and sundry "really". As I have said we don't really have enough info to give reasonable answers, though, with all the questions coming up due to this, these alone could help the OP analyse his issues?