Fire caused by electrical light fitting?

[jg999]

I'm investigating a serious house fire where the ground floor was severely damaged. The occupiers were on holiday at the time (luckily). The house is about 40 years old & of traditional construction for a 4 bed terraced.

Obviously i cannot go into too much detail but there is no evidence, or motive, for deliberate ignition.

There has been a number of 'anomalies' with the electrical supply over recent years- fuses blowing frequently for no reason and other electrical items burning out. Similar events have occurred in neighbouring houses. Excavation at the scene seems to lead to the fire starting within a ceiling light fiting in the lounge, although the light was not switched on. In fact all electrical appliances and switches were switched off (including a new fridge/freezer which had burned out the first time it was plugged in!)

Good old reliable notes from the college explain that an instantaneous electrical discharge could result in a temperature of up to 4000°C. As copper burns at between 1100°C to 2000°C, is it possible that the wiring (which I understand is as originally fiited) could have caught alight due to a discharge of this nature, spreading to the light shade? Or can anybody provide an alternative means whereby the light fitting could have ignited?

I would very much appreciate some advice on this!

[John Webb]

Dear jg999,
When you say 'the light fitting' was this the ceiling rose at ceiling level or the lampholder/lampshade? Or was it some other form of fitting?

You should bear in mind that the feed to lights runs (usually) from the fuse box to a ceiling rose where it is connected to terminal blocks and carries onto the next rose and so on. Switches are connected by a pair of cables from the live (phase) feed and back to a third terminal block in the rose and thence to the light fitting. So unless the fuse is removed or circuit breaker turned off for that circuit there will always be full volts at the ceiling rose. So if there is a poor connection or other fault there, it is possible for something to happen. Has the house ever had an IEE inspection to check insulation, earthing etc?

I would be inclined to delve into the history of previous 'Anomolies'.  Has the incoming mains been monitored for fluctuations? Is it an underground feed or overhead? Was there any evidence of thunderstorm activity which may have caused surges around the time of the fire? (Lightning strikes nearby can induce overvoltages even when they don't actually hit a house or cables.)

Hope the above may provoke some ideas.

[Martin Burford]

jg999

Interesting!....I would be looking at weather cobditions at the time of the fire as there has been considerable lightening activity recently.  also I would be taking an interest in previous supply history of the area as there is something curious about your notes of this.  Can't add to JSW's narrative.  I would be interested to read your final conclusions,
Conqueror

[kurnal]

jsw- Congratulations on an excellent summary. I have encountered something almost identical to this when a local substation problem (neutral fault i think)  caused over voltage surges to occur, numerous  appliances burning out  in a row of terraced houses over a period- especially appliances with clocks in. Nobody would believe the poor old consumers invloved until one morning we had a fire requiring the attendance of the service which if I recall involved the central heating programmer and pump. Eventually it was resolved- the  row  of houses was on generators for quite some time till it was sorted. As JSW indicates I think overhead supplies are more prone to this type of fault.

[Mike Buckley]

An obvious question strikes me. Given the house is about 40 years old, what is the state of the wiring and has it been tested recently? Also given the age of the house is there any evidence of DIY?

[jg999]

Many thanks for your replies so far, some very interesting reading!

There was a IEE inspection in 2001 which stated that the general condition of the installation was "Fair" yet the overall assessment of the installation was "Unsatisfactory". It went on to report that there was no RCD protection to the downstairs ring main and no CPC on the upstairs lighting circuit. The consumer unit and mains board was subsequently replaced (3 years later) but electrical reports still state "no CPC on lights".

There is no evidence of electrical storms that night (the fire started around 0345).

I am inclined to think the fire may have started in the ceiling rose, causing the wiring to burn & melt and therefore dropping the lightshade, bulb, holder and still burning wiring onto combustible materials below - in this case cardboard. Remains of the bulb glass show no discolouration from smoke and was found at the lowest level of excavation.

Allegedly the house next door had a kitchen fluorescent light fitting catch fire back in July, but as we know this is quite common. However, the number of reports of "faulty electrics" in neighbouring houses is quite extraordinary!

DIY to the mains electrical supply is not permitted in this house and no evidence was found. Nevertheless, we did find one table lamp plug with the 5 amp fuse wrapped in silver foil but this was remote from the fire scene.

I am very grateful for your help so far and would be very interested in any updates.

[Mike Buckley]

Check out the workshop report from the "Live Lear Pass It On" Fire Investigation Conference 1999 details in the papers section of the Firenet members area. It refers to some research work done by Neil Carey London FB and a paper is(was?) available.

[jg999]

Thanks Mike...I've searched all afternoon for a reference to this workshop report but cannot find it!?

[messy]

J999

London's Fire Investigator with electrical expertise is Nick Carey (not Neil). He has carried out interesting research into fires originating from electrical problems and has lectured worldwide

He is contactable via LFB,  or there's loads on Google about him.

Try the  IAAI website (where he is a committe member). They've even got a bulletin board like this where Nick moderates the 'Any Qustions' threads. Primarily for arson, I am sure the members there will offer help

http://www.iaai-uk.org.uk/ubb/toast.asp

If you get stuck, e-mail me for a direct number

Good luck

[Graeme]

As John mentioned the wiring could be "loop in" so the feed from the consumer unit would enter the ceiling rose and out again to the next one,so there is always 240v present.

If the flex for the lampholder was not supported inside the rose then all the weight of the light fitiing would have been on the terminals.

The fact that the lighting circuit has no CPC-circuit protecting conductor(earth) is a worry.

[Valiant Fire Academy]

This may be a belated reply  (new member) But whilst carrying out a FRA (FPWR) at two separate premises of an electrical store outlet, retailing many cheap imported electrical goods,  I have noted that italian ceiling light fittings with the bulb holder bayonet permanantly attached to the shade (Tiffany shade type) had deteriotated and become friable with use, reacting very much like old bakerlite fittings. Over time and with many bulb changes the crumbling plastic allows the bulb to arc the bayonet prongs almost welding it in and generating enough heat to combust. If this happens in an 'Electrical Store' the potential fire risk for consumers is self evident. J999 didn't  note the type of fitting. Regards Valiant

[jg999]

Many thanks for all your responses. Subsequent investigations by competent electrical safety engineers condemned the electrical installation in this particular premise and when inspecting other houses in the same road resulted in some occupants being relocated as an emergency preventative measure. One of the reports I received stated that it was extremely fortunate that occupants had not been electrocuted!

I remain uncertain as to how the light shade could have initially ignited as it was the old 'wire framed fabric with tassle' type and would have therefore been held at least 8-9 cm from the ceiling rose. I think this is one which will never be fully explained, but at least it is now almost certain that poor electrics was the cause!

Thanks again for your help.

jg999

[justpassinthru]

DIY to the mains electrical supply is not permitted in this house ....

we did find one table lamp plug with the 5 amp fuse wrapped in silver foil..

What do you mean by "not permitted"?   Who could "forbid" it, and on what authority, and how would any such prohibition be enforced?

And can you trust the sort of person who would wrap foil round a fuse to either take note of a prohibition, or to be safe at DIYing?

[Graeme]

DIY to the mains electrical supply is not permitted in this house ....

we did find one table lamp plug with the 5 amp fuse wrapped in silver foil..

What do you mean by "not permitted"?   Who could "forbid" it, and on what authority, and how would any such prohibition be enforced?

Part P

[justpassinthru]

Well - that doesn't really answer it.

"DIY to the mains electrical supply is not permitted in this house" sounds like something a bit more direct than one part of the Building Regulations.

A part which, BTW, does not forbid DIY electrical work, is not policed and enforced in any meaningful way, and imposes restricitions that are likely to be ignored (even if known of) by the sort of f***wit that would wrap foil around a fuse..

Anyway - it's not hugely important - I just wondered what jg999 meant by it.