Scrutable

To cap off this sh.tty year, 2020 takes things a bit too literally. There was an explosion this morning at the Wessex Water water recycling facility. It sounds like a solid biomass tank exploded (people are speculating that it was a methane build-up). Four people have been killed, a fifth has been injured. They were on the roof of the building when the explosion occurred. The police and fire service are keeping speculation to a minimum which is sensible, and an investigation will obviously take place.

If you want to discuss how 'one death is a tragedy, a million deaths are a statistic', can we have a separate thread to do that please?

This is an industrial accident that has happened at a place that has been working for decades without major incident. There are 7,078 sewage treatment works in the UK and I've not heard of an accident of this severity before. A quick google has failed to find anything for the UK (everything is dominated by this story), but a report from the US published in 2012 had very few fatalities across the nation (mean 3.2 per year between 1992 and 2010). Given that these facilities are normally incredibly safe what went wrong?

lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

plodder wrote: Thu Dec 03, 2020 6:54 pm lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

The police are saying it was a silo "that holds treated biosolids before it is recycled to land as an organic soil conditioner".

Though it's not been confirmed, the speculation I've seen is that the people who died were working on the roof at the time of the explosion. The roof was pretty much torn off (see the photo at the top of this article). I'm rather hoping they were killed by the force of the explosion as the alternative is really very grim indeed.

plodder wrote: Thu Dec 03, 2020 6:54 pm lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

One of the treatment places near me mixed two chemicals that shouldn't've been and made some horrible gas. Luckily, people don't like living near treatment places and no workers died, but many had respiratory problems after. Not sure if it was due to a mix up storing things or due to not making sure chemical 1 was flushed before putting in chemical 2, though.

There are so many things that could have happened, I’m not going to speculate. I do work with pressure vessels all the time, so I’ll be very interested in the investigation, but it’s going to be a while I expect.

I've moved some posts to a new Relative Mortality thread
viewtopic.php?f=10&p=59293#p59293

I would bet there was some "hot work" welding in other words going on on top of the tank.

Boustrophedon wrote: Thu Dec 03, 2020 10:30 pm I would bet there was some "hot work" welding in other words going on on top of the tank.

Hot work would only cause an explosion like that if there was air and fuel in the tank. If it’s anaerobic there shouldn’t be air in there.

monkey wrote: Thu Dec 03, 2020 7:45 pm

plodder wrote: Thu Dec 03, 2020 6:54 pm lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

One of the treatment places near me mixed two chemicals that shouldn't've been and made some horrible gas. Luckily, people don't like living near treatment places and no workers died, but many had respiratory problems after. Not sure if it was due to a mix up storing things or due to not making sure chemical 1 was flushed before putting in chemical 2, though.

Chlorine gas perhaps? Chlorine is used in water treatment.

Woodchopper wrote: Thu Dec 03, 2020 10:45 pm

monkey wrote: Thu Dec 03, 2020 7:45 pm

plodder wrote: Thu Dec 03, 2020 6:54 pm lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

One of the treatment places near me mixed two chemicals that shouldn't've been and made some horrible gas. Luckily, people don't like living near treatment places and no workers died, but many had respiratory problems after. Not sure if it was due to a mix up storing things or due to not making sure chemical 1 was flushed before putting in chemical 2, though.

Chlorine gas perhaps? Chlorine is used in water treatment.

I thought so but wasn't sure, but I just done a google, and an article says "An accidental mix of sodium hypochlorite (which is essentially bleach) and ferric sulfate caused a chlorine off gas". So yeah, good guess.

Turns out it was a delivery being put in the wrong tank too*. 55 people went to hospital, but I think they sent everyone who had been exposed to be checked, rather than just those who were in a bad way.

*I'm not suggesting that's what has happened at Avonmouth, I was just wanted to point out that the sort of thing suggested by Plodder does happen.

Grumble wrote: Thu Dec 03, 2020 10:40 pm

Boustrophedon wrote: Thu Dec 03, 2020 10:30 pm I would bet there was some "hot work" welding in other words going on on top of the tank.

Hot work would only cause an explosion like that if there was air and fuel in the tank. If it’s anaerobic there shouldn’t be air in there.

"Shouldn't." Quite, but I can't see any other source of an explosive gaseous mixture. The explosion obviously came from inside the tank, what else could it be? That's why I am speculating hot work, perhaps they let the air in by the operation they were carrying out?

Boustrophedon wrote: Thu Dec 03, 2020 11:18 pm

Grumble wrote: Thu Dec 03, 2020 10:40 pm

Boustrophedon wrote: Thu Dec 03, 2020 10:30 pm I would bet there was some "hot work" welding in other words going on on top of the tank.

Hot work would only cause an explosion like that if there was air and fuel in the tank. If it’s anaerobic there shouldn’t be air in there.

"Shouldn't." Quite, but I can't see any other source of an explosive gaseous mixture. The explosion obviously came from inside the tank, what else could it be? That's why I am speculating hot work, perhaps they let the air in by the operation they were carrying out?

Like I say, there are any number of possible causes. Another could be simple overpressurisation.

Woodchopper wrote: Thu Dec 03, 2020 10:45 pm

monkey wrote: Thu Dec 03, 2020 7:45 pm

plodder wrote: Thu Dec 03, 2020 6:54 pm lots of tricksy chemicals stored in bulk at places like this, lots of sweating of old assets too. one potentially hazardous operation is refilling the tanks with fresh chemicals , you really want to ensure the right chemical goes in the right tank. pure speculation of course.

One of the treatment places near me mixed two chemicals that shouldn't've been and made some horrible gas. Luckily, people don't like living near treatment places and no workers died, but many had respiratory problems after. Not sure if it was due to a mix up storing things or due to not making sure chemical 1 was flushed before putting in chemical 2, though.

Chlorine gas perhaps? Chlorine is used in water treatment.

This is a wastewater site, those chemicals are disinfectants used for potable water. Can’t remember the wastewater ones...

The explosion limits for methane are quite narrow (~4-15% v/v in air, compare that to hydrogen at 4-74% v/v in air) so it would require a lot of air to get into an anaerobic environment to allow for explosion. Not impossible but under anything like normal working conditions it would be unlikely.

An over pressure explosion can be devastating. This example of a LN2 tank where someone welded up the pressure relief valve was pretty destructive (PDF).

As mentioned upthread, highly unlikely that there's chlorine or chlorine producing chemicals on site as this is a waste water treatment site. That's why you'll see windsocks on any site that is processing potable water.

Looking at the design of the silo, it doesn't look like it's designed as a pressure vessel and the damage doesn't look like a failed pressure vessel.

This is definitely going to be a police/HSE investigation. At least everyone is accounted for and able to be recovered in a timely manner to enable them to be returned to their families

Dave, Plodder

Yes, the chlorine was just in relation to the other plant near monkey.

Chlorine isn't explosive (as far as I know) so it wouldn't have caused the explosion at Avonmouth.

Woodchopper wrote: Fri Dec 04, 2020 10:40 am Dave, Plodder

Yes, the chlorine was just in relation to the other plant near monkey.

Chlorine isn't explosive (as far as I know) so it wouldn't have caused the explosion at Avonmouth.

Yes, if chlorine is involved in an 'explosion' it's usually connected with the rupture of a pressure vessel.

From reports in the media, it does sound like whatever happened was quite energetic. A picture has emerged in some media reports showing a ball of flame around the same size as the top of the tank/silo

Woodchopper wrote: Fri Dec 04, 2020 10:40 am Dave, Plodder

Yes, the chlorine was just in relation to the other plant near monkey.

Chlorine isn't explosive (as far as I know) so it wouldn't have caused the explosion at Avonmouth.

You have to be careful with handling chlorine because it can contain the sensitive explosive nitrogen trichloride. Larger quantities, we used 70kg or 100kg cylinders on the pilot plant, on the works it came in 21tonne road tankers: liquid chlorine is discharged into a vaporise to produce chlorine gas, evaporating from the cylinder can lead to a build up of nitrogen trichloride and an explosion. This clearly didn't happen in this case.
https://standards.globalspec.com/std/14 ... mphlet-152

Woodchopper wrote: Fri Dec 04, 2020 10:40 am Dave, Plodder

Yes, the chlorine was just in relation to the other plant near monkey.

Chlorine isn't explosive (as far as I know) so it wouldn't have caused the explosion at Avonmouth.

And I was only giving that as an example of accidently mixing stuff and making Bad Things happen.

Still very early days yet but some details appear to be emerging about what happened.

The focus of the explosion remains the biosolids silo.

It is believed the five people were all working on top of or near the silo.

The dangers associated with silos containing biosolids are well known in the industry. The Health and Safety Executive (HSE) has previously warned that methane can be a risk, as can “sewage dust”.

Concern about build-ups of pressure in storage silos at water treatment plants has also been flagged up as a cause for concern but there has been no incident comparable to the Avonmouth explosion in the UK. [my emphasis]

I suspect/hope the fact this is such an unusual industrial incident is going to result in a very thorough investigation. I don't know what the normal timescales are for these sorts of investigations but as it's local (one of the dead men is reported to have been from Clevedon, which is the next town over from me) I'll keep an eye out in the local press for updates.

Fishnut wrote: Fri Dec 04, 2020 5:03 pm I suspect/hope the fact this is such an unusual industrial incident is going to result in a very thorough investigation. I don't know what the normal timescales are for these sorts of investigations but as it's local (one of the dead men is reported to have been from Clevedon, which is the next town over from me) I'll keep an eye out in the local press for updates.

For investigations and prosecutions it can take quite a long time

BBC wrote: Two recycling companies and two people linked to them are to be charged over the deaths of five African men who died when a concrete wall fell on them.

Almamo Jammeh, Ousmane Diaby, Bangally Dukureh, Saibo Sillah and Mahamadou Jagana died at Shredmet's premises in Birmingham on 7 July 2016.

BBC News

OneOffDave wrote: Fri Dec 04, 2020 5:38 pm

BBC wrote: Two recycling companies and two people linked to them are to be charged over the deaths of five African men who died when a concrete wall fell on them.

Almamo Jammeh, Ousmane Diaby, Bangally Dukureh, Saibo Sillah and Mahamadou Jagana died at Shredmet's premises in Birmingham on 7 July 2016.

BBC News

From that article:

The men could only be identified by their fingerprints.

The names of those killed at Avonmouth have been released. One was a 16 year old apprentice.

Fishnut wrote: Fri Dec 04, 2020 7:14 pm The names of those killed at Avonmouth have been released. One was a 16 year old apprentice.

How awful. We have an apprentice and I live in fear that he’s going to hurt himself somehow.

OneOffDave wrote: Fri Dec 04, 2020 9:54 am Looking at the design of the silo, it doesn't look like it's designed as a pressure vessel and the damage doesn't look like a failed pressure vessel.

Thankfully I’m no expert on what a failed pressure vessel looks like, but the design looks like it could be meant to accommodate some pressure to me. Not a lot, sure, but any amount of pressure over ambient in a vessel that size would meet the criteria (250 bar.litres). The tank has clearly burst, but what the difference looks like between a burst from an explosion versus a release of over pressure I couldn’t say.

Fishnut wrote: Fri Dec 04, 2020 7:14 pm
From that article:

The men could only be identified by their fingerprints.

The preferred methods of identification in multi casualty incidents are dental records, fingerprints and DNA in that order. There may be issues with using dental records if a dentist who has treated the possible victim recently cannot be located as opposed to anything connected to the state of the remains . This is obviously simpler with what are referred to as 'closed' incidents where you know the members of the potential pool of victims as opposed to things like transport incidents where you don't.

I had my disaster victim identification awareness refresher training last week