House explosion in Christchurch.

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JaseNZ

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#252994 20-Jul-2019 18:18

I am sure you have all seen the pictures of the house explosion in Christchurch, A suspected gas explosion with work being carried out on the dwelling the day before for some gas related issue.

I am sure the investigation will show the exact problem.

It amazes me that nobody was killed, 5 people in the house itself, I mean look at the devastation and no death it just amazes me. I do understand some people are in a pretty bad way in hospital, My thought's go out to them and all the people around that area that have been badly affected.

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tdgeek

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#2280375 20-Jul-2019 18:24

Must be a gas leak in the gas fire that was fixed the day before. But I had a leak in our bottle connection outside, I could smell it, got it fixed. @Fred99 mentioned in another thread that alarms could be used, which assumes no smell? It seems in this case gas leaked so it was building up in the house, and perhaps a light turned on or cooking hob or the gas heater ignited it.

Dratsab

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#2280410 20-Jul-2019 19:39

JaseNZ: It amazes me that nobody was killed

This, so much. Although it's not certain everyone will pull through.

Fred99

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#2280421 20-Jul-2019 20:05

tdgeek:

I could smell it, got it fixed. @Fred99 mentioned in another thread that alarms could be used, which assumes no smell?

There's a smell all right. As the gas itself is effectively odourless, they add mercaptans to LPG and mains gas so that you can smell a leak. But there are still potential problems.

As I understand it, when you're asleep, you don't smell anything, the olfactory part of your brain is switched off. This a big issue with house fires, people don't wake up with the smell of smoke - by the time something else related to the fire wakes them up it's either too late to get out , or they asphyxiate while still asleep in bed. Hence cheap smoke alarms are a very good idea.

LPG is heavier than air, unless there's air circulation it stays low, so you could get an explosive concentration of gas at ground level, but not notice it at nose level.

As for the alarms, I think the one I have in the boat cost $200, and you'd probably need several in a house - and they'd have to be checked and probably replaced regularly. (The one I have on the boat is only powered up a few weeks a year).

tdgeek

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#2280431 20-Jul-2019 20:43

Fred99:

tdgeek:

I could smell it, got it fixed. @Fred99 mentioned in another thread that alarms could be used, which assumes no smell?

There's a smell all right. As the gas itself is effectively odourless, they add mercaptans to LPG and mains gas so that you can smell a leak. But there are still potential problems.

As I understand it, when you're asleep, you don't smell anything, the olfactory part of your brain is switched off. This a big issue with house fires, people don't wake up with the smell of smoke - by the time something else related to the fire wakes them up it's either too late to get out , or they asphyxiate while still asleep in bed. Hence cheap smoke alarms are a very good idea.

LPG is heavier than air, unless there's air circulation it stays low, so you could get an explosive concentration of gas at ground level, but not notice it at nose level.

As for the alarms, I think the one I have in the boat cost $200, and you'd probably need several in a house - and they'd have to be checked and probably replaced regularly. (The one I have on the boat is only powered up a few weeks a year).

Thanks for that. Yes, when my bottle connector was leaking I could smell a whiff, so I kneeled down to check if it was gas. I forget when the house exploded, but it was early morning. Maybe something ignited before the people got up.

CYaBro

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#2280457 20-Jul-2019 21:14

Is the reticulated gas different to what you get in the bottles?
We had a leak in our outside bottles and I could smell it on the other side of the house, also outside.
So if this house had a leak inside surely you’d smell it no problem?

Dratsab

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#2280464 20-Jul-2019 21:28

CYaBro: Is the reticulated gas different to what you get in the bottles?
We had a leak in our outside bottles and I could smell it on the other side of the house, also outside.
So if this house had a leak inside surely you’d smell it no problem?

Sounds like the occupants were older people so perhaps a diminished sense of smell, and/or not enough realisation that any smell at all might be indicative of an explosive concentration of gas. Really, all anyone can do is speculate at this stage.

Geektastic

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#2280465 20-Jul-2019 21:28

My wife's immediate response was "Meth cooks get it wrong"!

I said that seemed unlikely in this case, although not uncommon.

Jase2985

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#2280531 20-Jul-2019 23:03

Fred99:

LPG is heavier than air, unless there's air circulation it stays low, so you could get an explosive concentration of gas at ground level, but not notice it at nose level.

but mains gas is lighter than air isnt it?

i suspect its all concentrated under the roof in the ceiling given the damage to the house and the lack of a real fire.

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#2280536 20-Jul-2019 23:41

Jase2985:

but mains gas is lighter than air isnt it?

i suspect its all concentrated under the roof in the ceiling given the damage to the house and the lack of a real fire.

Normally the term "mains gas" is used to refer to reticulated natural gas systems such as the one covering most north island major cities (not every street, but a decent number) which is fed from Taranaki. Natural gas is also very common in north america & europe.

There is no natural gas network in the south island.

But (relatively few) area's have a reticulated LPG network. I assume it is the same blend you get in bbq and 45kg bottles, but without the hassle of the bottles themselves. The list is at the bottom of this page:

https://www.ongas.co.nz/your-home/bottled-or-piped-lpg-supply

These are fed by a bulk vessel or array of vessels, topped up by LPG tanker trucks. Natural gas cannot be easily stored, or transported by means other than pipework, as it requires cryogenic temperatures to store it in a reasonable volume tank.

For reference:

Natural gas is mainly methane, a lighter than air gas.
LPG is Propane and/or Butane, heavier than air gasses.

Work-safe notes the natural gas will disperse relatively easy compared to LPG, and the latter is therefor more prone to catch fire or explode if a leak occurs. In yachts, the safety rules require "turn gas off at bottle" signs, and the gas bottle to be kept in a self draining locker or outside, in order to reduce the risk of LPG pooling in the bilge.

https://worksafe.govt.nz/managing-health-and-safety/consumers/gas-2/what-is-natural-gas/

Both gases have odor added for consumer use, but are naturally odorless. I have done a bit of work in a plant that uses industrial quantities of un-odourised gas, fairly intense environment. nylon hi vis vests are banned due to risk of static sparking, and anybody doing anything that could create a spark (i.e. using a consumer grade camera) has to get a permit and carry a gas detector.

Goosey

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#2280538 21-Jul-2019 00:24

gas we'll find out in due course....

im eager to know why they couldnt smell anything..... perhaps ceiling pipework leaking.......and all that smelly gas filling up the roof cavity until some one switches on the HRV or bathroom extractor fan causing an arc somewhere?

freitasm

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#2280589 21-Jul-2019 09:38

Ok folks. No naming the person or company here until investigation is complete.

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raytaylor

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#2280639 21-Jul-2019 11:57

CYaBro: Is the reticulated gas different to what you get in the bottles?
We had a leak in our outside bottles and I could smell it on the other side of the house, also outside.
So if this house had a leak inside surely you’d smell it no problem?

From memory the reticulated gas we had in upper hutt just smelled like rotting cabbage.

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DarthKermit

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#2280644 21-Jul-2019 12:09

freitasm:

Ok folks. No naming the person or company here until investigation is complete.

Stuff have an article naming the company already. I will abide by what you have said. It would be unfair to assume poor workmanship. Could be a defect within the gas heater for all anyone knows at this stage.

JaseNZ

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#2280645 21-Jul-2019 12:13

DarthKermit:

freitasm:

Ok folks. No naming the person or company here until investigation is complete.

Stuff have an article naming the company already. I will abide by what you have said. It would be unfair to assume poor workmanship. Could be a defect within the gas heater for all anyone knows at this stage.

Completely agree I bet the guy is feeling devastated regardless of what the cause was.

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tdgeek

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#2280652 21-Jul-2019 12:32

DarthKermit:

freitasm:

Ok folks. No naming the person or company here until investigation is complete.

Stuff have an article naming the company already. I will abide by what you have said. It would be unfair to assume poor workmanship. Could be a defect within the gas heater for all anyone knows at this stage.

Saw that, and that's so poor. Guilty till proven innocent. All in the name of a good sorry, like F

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