Inquest on scalded baby / faulty immersion heater

[Lobster]

I noticed on the news last night that the inquest is under way on that awful case of the baby who was scalded to death a tear or so back, when a tankful of boiling water came through her bedroom ceiling:

TV bulletin helpfully showed a clip of a reporter sitting in an attic next to a plastic CW tank, and explaining how 3.5 million homes are potentially at risk of a similar disaster.

Visions of half the population phoning their plumbers this morning to come and do safety checks...

I'm not familiar with these immersion heater systems, but as the owner of an unvented gas-fired system whose emergency overflow has the overheated hot water dumped outside the building at ground level, isn't there something fundamentally a bit nuts about a system which is designed to dump it above the ceiling into a plastic tank which is melted by boiling water??

David

[Si]

In message , Lobster writes

Wife was freaked by the above report when I confirmed that it's exactly the setup we have here. OTOH, our CW tank in the loft, if it collapsed, is placed so that it would flood the landing and down the stairs rather than into a bedroom. I also reassured her that we would hear the HW overflow dripping into the CW tank and/or notice the HW tank getting overly hot and/or notice the CW tank warning pipe dripping well before anything collapsed.

ISTM the accident happened because the family had just moved into a house with which they were unfamiliar and didn't react to the signs warning them that something was going wrong.

[John]

My understanding is that newer immersion heaters have an additional thermostat to prevent this problem ( as a result of an earlier similar incident)

Perhaps someone can confirm what a safer immersion heater looks like to put minds at ease. (I have a combi)

[Huge]

We heard the tank "bumping" when it happened here. I swapped the immersion for one with an overtemperature trip. Which falses all the time. Still, I suppose having no hot water is better than being boiled alive.

[Huge]

Mine has a *tiny* little blue button sticking up through the top with the word "reset" next to it. If it goes overtemperature, the button pops up and has to be puched back down.

[Mike Tomlinson]

In article , Si writes

Including scalding water coming out of the cold tap in the bathroom. I mean, come on? Who would ignore that?

TV also showed a clip of the parents arriving at the inquest smiling and waving, which I found rather odd.

[John]

Lots of people behave very inappropriately at courts - perhaps the sight of a camera and they think they are on Big Brother

[The Natural Philosopher]

Cansomeone expalin EXACTLY what happened?

I was expecting this thread.. and I think a clear explanation is useful to all..here.

I know that in my case, with PHW, there are safety circuits everywhere for just this kind of event..I assume this was simply a stock unpressurised tank that boiled back into a header tank? and that collapsed and dumped hot water on the baybee?

Seems strange that the header couldn't take 100C..

[David Hansen]

On Tue, 08 Jan 2008 10:06:56 GMT someone who may be Lobster wrote this:-

I had assumed it was a pressurised system, but was wrong about that.

Traditionally in Scotland the pipe concerned rises through the roof and then bends through 180 degrees, in order to allow water to land on the roof. This avoids the remote possibility of there being such an accident, at the cost of a roof penetration.

[David Hansen]

On Tue, 8 Jan 2008 10:23:12 +0000 someone who may be Si wrote this:-

That appears to be the case.

[David Hansen]

On Tue, 08 Jan 2008 13:06:59 +0000 someone who may be The Natural Philosopher wrote this:-

It looks like the following sequence of events:

1) The immersion heater was switched on for the first time in the new tenancy and left switched on. 2) The thermostat failed, or had failed some time before. 4) It was an older style of immersion heater without a secondary overheat sensor that has to be reset by hand. 5) Very hot water flowed via the vent pipe into the cold water storage tank. 6) There would then be a circulation of hot water around the circuit tank - "cold" feed to cylinder - cylinder - vent pipe-tank. 7) When hot water came out of the "cold" taps no action was taken. 8) Eventually the cold water tank failed.

If this was happening every week it would be a reason to change things. However, awful as this accident was 100% safety is not possible. Far more babies die from other things.

[RobertL]

Surely this must mean that the high point of the vent pipe was too low. The vent pipe goes up significantly higher than the top of the storage tank exactly so that this kind of thing does not happen, does it not?

Robert

[David Hansen]

On Tue, 8 Jan 2008 06:26:34 -0800 (PST) someone who may be RobertL wrote this:-

The vent pipe goes up higher than the top of the storage tank and then bends over into it. When a bubble of air or steam is rising up the vent pipe it will push any water ahead of it and into the cold water storage tank.

When temperature control of an immersion heater fails it is likely to heat the water up so much that steam is formed. As a result water will circulate around the circuit I outlined and get increasingly hot each time it passes through the cylinder.

[Peter Parry]

It appears to have been a standard un vented system with an immersion heater. The immersion heater thermostat failed so leaving it on all the time.

The water in the hot water tank boiled and the steam forced water in the vertical leg of the overflow pipe into the cold water storage tank (the hot water tank vent normally overhanging the cold tank rather than the header tank).

The water displaced by boiling was replaced by cold water from the storage tank as normal which refilled the vertical vent with hot water which was promptly expelled by the boiling water below.

The continuous boiling set up a form of thermal pump action where near boiling water went into the cold storage tank via the vent and was replaced via the cold feed to the bottom of the tank. Eventually the cold water tank was nearly at boiling point, the same temperature as the storage cylinder, and the plastic sides deformed dumping the contents on the ceiling which collapsed onto the child underneath. The tanks are rated up to about 80deg C I believe so the immersion heater must have been boiling water for some time.

It isn't clear how no one noticed anything going on as it would have been a fairly noisy process and the scalding water from all the taps should have prompted someone to turn the immersion heater off.

[The Natural Philosopher]

How and why?

True.

[The Natural Philosopher]

That's the weak point then. Make em take 100C.

I believe so the immersion heater

True, but people are complete dickheads most of teh time. "I expect thats how its supposed to work, dear"

[Lobster]

It just collapsed apparently, ie presumably went floppy under the sustained heat.

The inquest is still ongoing so more info will be forthcoming no doubt. The radio news just now reported that the parents had turned the thermostat up higher than the Council reccommended, to 80 def F - which strikes me as being a totally irrelevant piece of information.

David

[Lobster]

The radio bulletin I mentioned earlier said that the tank was fitted 30 years ago and was of the correct standard for that time, which implies to me that maybe modern tanks now *will* take 100 C.

David

[The Natural Philosopher]

80F? thats not even warm! 80C shirley?

- which

[Owain]

My parents had this symptom - but on a gravity circulation hot water system from a Parkray solid-fuel roomheater/boiler, which can't be easily turned off, when it "ran away" because of strong wind in a certain direction.

Owain