St Helier explosion.

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St Helier explosion.

Post by Boustrophedon » Sun Dec 11, 2022 9:17 pm

I'm probably wrong, but the one video of the explosion shows a blast that looks very energetic with lots of burning shrapnel being blasted upwards at high speed. I am not an explosives expert, but it looks far too energetic for a gas explosion.
On the other hand the residents had complained of a 'smell of gas' earlier.

A video from a security camera here: https://www.itv.com/news/channel/2022-1 ... -explosion
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Re: St Helier explosion.

Post by Brightonian » Sun Dec 11, 2022 9:36 pm

Boustrophedon wrote:
Sun Dec 11, 2022 9:17 pm
I'm probably wrong, but the one video of the explosion shows a blast that looks very energetic with lots of burning shrapnel being blasted upwards at high speed. I am not an explosives expert, but it looks far too energetic for a gas explosion.
On the other hand the residents had complained of a 'smell of gas' earlier.

A video from a security camera here: https://www.itv.com/news/channel/2022-1 ... -explosion
Resident of a house in south London said to have reported the smell of gas before an explosion there: https://www.itv.com/news/london/2022-08 ... -explosion

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Re: St Helier explosion.

Post by dyqik » Sun Dec 11, 2022 10:31 pm

Gas leaks often happen in basements or under floors (e.g. due to corrosion of the pipe entering the building). If the explosion happens there, then the whole house above is blown upwards.

This is particularly true for brick buildings where the floors, ceilings and roof are lighter than the walls.

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Re: St Helier explosion.

Post by insignificant » Sun Dec 11, 2022 10:41 pm

mains gas here is manufactured from imported LPG

(properties that can't be connected to the mains will have external tanks)

local gas supplier used to have more details about its composition / energy density on their website, but not any more

but what are the plausible alternatives to a gas explosion?
Last edited by insignificant on Sun Dec 11, 2022 10:46 pm, edited 1 time in total.

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Re: St Helier explosion.

Post by Gfamily » Sun Dec 11, 2022 10:46 pm

... [A]n inquiry has begun into the action of the fire service in the hours before the explosion at 4am on Saturday.
Less than eight hours before the three-storey Haut du Mont apartments on Pier Road were enveloped in a fireball, firefighters were called to the site at 8.36pm on Friday after residents reported a suspected gas leak.

[Jersey’s fire chief, Paul Brown] said he would be “transparent” about the events leading up to the explosion and that something had gone “horribly wrong” but would not say whether any members of staff had been suspended.
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Re: St Helier explosion.

Post by dyqik » Sun Dec 11, 2022 11:50 pm

insignificant wrote:
Sun Dec 11, 2022 10:41 pm
mains gas here is manufactured from imported LPG

(properties that can't be connected to the mains will have external tanks)

local gas supplier used to have more details about its composition / energy density on their website, but not any more

but what are the plausible alternatives to a gas explosion?
Explosion of petrol or canister gas stored in a basement - i.e. roughly a gas leak.

WW2 Unexploded Ordnance.

Meth lab in the basement (yeah, no).


There was a string of roughly 50 gas explosions here in houses in one day a few years back after the mains gas pressure regulation failed and the pipes were overpressurized.

Also, a house in my small town (~3000 houses) exploded last year due to a gas leak in the supply pipe outside the house that fed gas into the basement.

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Re: St Helier explosion.

Post by Martin_B » Mon Dec 12, 2022 12:54 am

Boustrophedon wrote:
Sun Dec 11, 2022 9:17 pm
I'm probably wrong, but the one video of the explosion shows a blast that looks very energetic with lots of burning shrapnel being blasted upwards at high speed. I am not an explosives expert, but it looks far too energetic for a gas explosion.
On the other hand the residents had complained of a 'smell of gas' earlier.

A video from a security camera here: https://www.itv.com/news/channel/2022-1 ... -explosion
I think the reason you think that it isn't a gas explosion is because it doesn't look like a Hollywood special-effects gas explosion. But it doesn't look too far out for a gas explosion to me, and I've probably got more experience with those than most folks here.

The gas will have built up before the explosion, so there could be a fair quantity of gas in the house waiting to explode. Gas explosions (deflagrations) start out small and slow but then accelerate as the flame front moves through the gas cloud and the explosion overpressure increases. This is as opposed to detonations which people are more used to seeing where the explosion overpressure decreases exponentially as it moves away from the explosion.

The shrapnel will be bits of the building being shot upwards, and it goes upwards because the walls of the building (and the buildings on either side) make the easiest path for the explosion overpressure to vent upwards.
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Re: St Helier explosion.

Post by IvanV » Mon Dec 12, 2022 10:42 am

Natural gas building explosions can be much larger than this one, as the 2017 New Ferry Explosion in Liverpool illustrates. Over 10 properties were demolished and over 100 badly damaged. Fortunately it happened in a retail block outside trading hours, so no one was killed - the demolished properties were all retail units. But approaching 100 people were injured in nearby residential property, and a similar number made homeless. Damage occurred over an area of 1.5sq km, which would suggest in places up to about 800m from the explosion site.

Now that one was caused deliberately, as attempted insurance fraud. The scale of the explosion was probably not the perpetrator's intention. They probably had in mind typical domestic gas explosions where the damage is largely confined to the one property. But it happened in just the same way as a typical domestic gas explosion - a gas leak - in this case deliberately caused - built up a reservoir of gas in a room, and was then triggered by something, in this case an electric heater. The fact that the scenario allowed such a large explosion was doubtless down to details that don't usually work out just like that.

Hydrogen explosions can be much more powerful, as illustrated by the 1985 Heroya ammonia plant explosion in Norway.

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Re: St Helier explosion.

Post by Tessa K » Mon Dec 12, 2022 3:33 pm

dyqik wrote:
Sun Dec 11, 2022 11:50 pm
insignificant wrote:
Sun Dec 11, 2022 10:41 pm
mains gas here is manufactured from imported LPG

(properties that can't be connected to the mains will have external tanks)

local gas supplier used to have more details about its composition / energy density on their website, but not any more

but what are the plausible alternatives to a gas explosion?
Explosion of petrol or canister gas stored in a basement - i.e. roughly a gas leak.

WW2 Unexploded Ordnance.

Meth lab in the basement (yeah, no).


There was a string of roughly 50 gas explosions here in houses in one day a few years back after the mains gas pressure regulation failed and the pipes were overpressurized.

Also, a house in my small town (~3000 houses) exploded last year due to a gas leak in the supply pipe outside the house that fed gas into the basement.
There was a meth lab explosion near me a while ago. That was mostly fire and a lot of black smoke (n=1). We're classy round here.

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Re: St Helier explosion.

Post by KAJ » Mon Dec 12, 2022 6:31 pm


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Re: St Helier explosion.

Post by Grumble » Mon Dec 12, 2022 8:16 pm

Is gas odourant added to bottled propane/butane?
A bit churlish

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Re: St Helier explosion.

Post by KAJ » Mon Dec 12, 2022 8:22 pm

Grumble wrote:
Mon Dec 12, 2022 8:16 pm
Is gas odourant added to bottled propane/butane?
HSE says
LPG can be obtained primarily as propane, butane or a mixture of the two. A powerful odorant is added so that it is easily detected.

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Re: St Helier explosion.

Post by Boustrophedon » Mon Dec 12, 2022 10:39 pm

KAJ wrote:
Mon Dec 12, 2022 8:22 pm
Grumble wrote:
Mon Dec 12, 2022 8:16 pm
Is gas odourant added to bottled propane/butane?
HSE says
LPG can be obtained primarily as propane, butane or a mixture of the two. A powerful odorant is added so that it is easily detected.
Is the same odorant added to liquified supplied in bottles, 'calor gas', as to mains gas?
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Re: St Helier explosion.

Post by Martin_B » Mon Dec 12, 2022 11:51 pm

Boustrophedon wrote:
Mon Dec 12, 2022 10:39 pm
KAJ wrote:
Mon Dec 12, 2022 8:22 pm
Grumble wrote:
Mon Dec 12, 2022 8:16 pm
Is gas odourant added to bottled propane/butane?
HSE says
LPG can be obtained primarily as propane, butane or a mixture of the two. A powerful odorant is added so that it is easily detected.
Is the same odorant added to liquified supplied in bottles, 'calor gas', as to mains gas?
The same class of odorant is added (I can't say whether it's *exactly* the same) and is most commonly a mercaptan of some sort; methanethiol or ethanethiol are quite easy to synthesise and don't need to be present in significant quantities (~10 ppm) to be detectable.
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Re: St Helier explosion.

Post by Boustrophedon » Tue Dec 13, 2022 10:46 am

Martin_B wrote:
Mon Dec 12, 2022 11:51 pm
The same class of odorant is added (I can't say whether it's *exactly* the same) and is most commonly a mercaptan of some sort; methanethiol or ethanethiol are quite easy to synthesise and don't need to be present in significant quantities (~10 ppm) to be detectable.
I just wondered whether it was made possible to smell the difference.
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Re: St Helier explosion.

Post by Brightonian » Tue Dec 13, 2022 11:51 am

Would it be feasible to install gas detectors, in the same way that smoke and carbon monoxide detectors are routinely installed these days? Or would that be overkill, even if possible (I know nothing about the science or engineering or technology of this*)?

* or of anything really ;)

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Re: St Helier explosion.

Post by Grumble » Tue Dec 13, 2022 12:10 pm

Brightonian wrote:
Tue Dec 13, 2022 11:51 am
Would it be feasible to install gas detectors, in the same way that smoke and carbon monoxide detectors are routinely installed these days? Or would that be overkill, even if possible (I know nothing about the science or engineering or technology of this*)?

* or of anything really ;)
Yes, we have them installed in our boiler room at work. Need to match the detector and the location to the type of gas. Methane for example is lighter than air, but propane and butane are denser, so the sensors may need to be on the floor or the ceiling. Cost may be prohibitive and they aren’t really much better than the human nose when the odourant is added. However people aren’t around all the time and you can also become accustomed to smells and start to ignore them.
A bit churlish

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Re: St Helier explosion.

Post by shpalman » Tue Dec 13, 2022 12:24 pm

Grumble wrote:
Tue Dec 13, 2022 12:10 pm
Brightonian wrote:
Tue Dec 13, 2022 11:51 am
Would it be feasible to install gas detectors, in the same way that smoke and carbon monoxide detectors are routinely installed these days? Or would that be overkill, even if possible (I know nothing about the science or engineering or technology of this*)?

* or of anything really ;)
Yes, we have them installed in our boiler room at work. Need to match the detector and the location to the type of gas. Methane for example is lighter than air, but propane and butane are denser, so the sensors may need to be on the floor or the ceiling. Cost may be prohibitive and they aren’t really much better than the human nose when the odourant is added. However people aren’t around all the time and you can also become accustomed to smells and start to ignore them.
Our lab has detectors for silane and germane, the analogues of methane from further down group IV. (We also have detectors for gases less relevant to the discussion.)
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Re: St Helier explosion.

Post by Grumble » Tue Dec 13, 2022 12:49 pm

shpalman wrote:
Tue Dec 13, 2022 12:24 pm
Grumble wrote:
Tue Dec 13, 2022 12:10 pm
Brightonian wrote:
Tue Dec 13, 2022 11:51 am
Would it be feasible to install gas detectors, in the same way that smoke and carbon monoxide detectors are routinely installed these days? Or would that be overkill, even if possible (I know nothing about the science or engineering or technology of this*)?

* or of anything really ;)
Yes, we have them installed in our boiler room at work. Need to match the detector and the location to the type of gas. Methane for example is lighter than air, but propane and butane are denser, so the sensors may need to be on the floor or the ceiling. Cost may be prohibitive and they aren’t really much better than the human nose when the odourant is added. However people aren’t around all the time and you can also become accustomed to smells and start to ignore them.
Our lab has detectors for silane and germane, the analogues of methane from further down group IV. (We also have detectors for gases less relevant to the discussion.)
There are detectors available for pretty much any gas, whether it’s economical to install detectors is very location dependent
A bit churlish

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Re: St Helier explosion.

Post by Martin_B » Wed Dec 14, 2022 1:29 am

Grumble wrote:
Tue Dec 13, 2022 12:10 pm
Brightonian wrote:
Tue Dec 13, 2022 11:51 am
Would it be feasible to install gas detectors, in the same way that smoke and carbon monoxide detectors are routinely installed these days? Or would that be overkill, even if possible (I know nothing about the science or engineering or technology of this*)?

* or of anything really ;)
Yes, we have them installed in our boiler room at work. Need to match the detector and the location to the type of gas. Methane for example is lighter than air, but propane and butane are denser, so the sensors may need to be on the floor or the ceiling. Cost may be prohibitive and they aren’t really much better than the human nose when the odourant is added. However people aren’t around all the time and you can also become accustomed to smells and start to ignore them.
I'd say typically they are less good than the human nose - in order to prevent false positives the detectors are typically designed to go off at ~10% of lower flammable limit (so ~0.5% methane in air) and the odorants added usually enable people to smell gas below this. As you say, they're really for areas where there isn't a constant human presence.
Boustrophedon wrote:
Tue Dec 13, 2022 10:46 am
Martin_B wrote:
Mon Dec 12, 2022 11:51 pm
The same class of odorant is added (I can't say whether it's *exactly* the same) and is most commonly a mercaptan of some sort; methanethiol or ethanethiol are quite easy to synthesise and don't need to be present in significant quantities (~10 ppm) to be detectable.
I just wondered whether it was made possible to smell the difference.
No, you can't smell the difference between natural gas and bottled gas as both are essentially odourless without the odorant added, and the odorants used are 'standardised'; mainly because people need to be familiar with the eggy/garlicy smell and associating it with gas.
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Re: St Helier explosion.

Post by Brightonian » Wed Dec 14, 2022 1:11 pm

Seems there had been mains gas after all, but it was disconnected a few months ago.
Chief executive of Andium Homes wrote:"There was a redundant Island Energy supply at Haut du Mont but as Island Energy have confirmed, no gas was being consumed on site either by us or our residents."

He said the company asked for the redundant supply to be disconnected from the mains network in September.
https://www.bbc.com/news/world-europe-jersey-63957055

So maybe the old supply wasn't properly capped.

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Re: St Helier explosion.

Post by Boustrophedon » Wed Dec 14, 2022 4:03 pm

Brightonian wrote:
Wed Dec 14, 2022 1:11 pm


So maybe the old supply wasn't properly capped.
I'd put money on that.
At uni one of the professors lectured us about design and showed us the gas coupling nut that failed, causing the Ronan Point disaster. Too big a chamfer left too little metal holding the joint together.
Ronan point gas fitting.jpg
Ronan point gas fitting.jpg (96.89 KiB) Viewed 372 times
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Re: St Helier explosion.

Post by dyqik » Wed Dec 14, 2022 11:43 pm

The gas explosion in my town last year they I mentioned above was caused by the pipe into the building corroding between the main and the building walls, and then gas running into the building basement along the outside of pipe.

Everything would have looked fine on the inside of the building.

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Re: St Helier explosion.

Post by EACLucifer » Thu Dec 15, 2022 6:27 am

dyqik wrote:
Wed Dec 14, 2022 11:43 pm
The gas explosion in my town last year they I mentioned above was caused by the pipe into the building corroding between the main and the building walls, and then gas running into the building basement along the outside of pipe.

Everything would have looked fine on the inside of the building.
Back in late 2018 I had to evacuate for several weeks due to a very similar scenario. It was pretty hairy evacuating, and had to have the gas levels double checked in order to put the power back on briefly to get the garage door open, as without the trike, I wasn't going to be able to take the chair with me. Not a fun experience, and the f.ckers took forever to find the leak and get it dealt with, as it was some way away and flowing along the cavity that had formed around the gas main. It affected quite a few houses.

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Re: St Helier explosion.

Post by Bird on a Fire » Thu Dec 15, 2022 2:20 pm

Martin_B wrote:
Mon Dec 12, 2022 11:51 pm
Boustrophedon wrote:
Mon Dec 12, 2022 10:39 pm
KAJ wrote:
Mon Dec 12, 2022 8:22 pm

HSE says
Is the same odorant added to liquified supplied in bottles, 'calor gas', as to mains gas?
The same class of odorant is added (I can't say whether it's *exactly* the same) and is most commonly a mercaptan of some sort; methanethiol or ethanethiol are quite easy to synthesise and don't need to be present in significant quantities (~10 ppm) to be detectable.
No way! So butane doesn't actually smell like nasty old farts? Every day's a school day.
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