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Off in the distance
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May 2016

The Bellinghman
Date: 2011-08-11 20:10
Subject: Sorry
Security: Public
I appears that I need to apologise to the north half of Royston tonight.

It started a little before 16:00. I was working away at some code that is meant to generate PDF files, trying to persuade an underlying component of the virtues of CMYK, when beyond my monitor, I saw something flying up into the air, trailing coloured smoke. Since this is an industrial estate, on the north edge of a small town, my brain contradicted my immediate first reaction, which was that someone had just fired a smoke grenade.

Yes, I know there have been rioters in some parts of England, but for Royston, mid afternoon, to be the first place that British police started deploying such countermeasures? No way. It must have been an odd reflection on the inside of the window.

But I looked again, and could see a yellowy-brown smudge drifting leftwards behind the Hotel Chocolat offices.

OK, something really there, and it was just our side of a building that is on the main road of which our office's side road is.

Well, someone had had a mishap.

Presumably whichever company it was would sort it out pretty sharpish. I was fairly sure it was a company that did printed circuit boards.

And so for five or ten minutes, we watched from a distance, and our disquiet mounted, since there was now quite a strong plume of ochre smoke coming from behind that hedge. After a bit, I wandered out through our car park, across the car park beyond (the one shared by us, Hotel Chocolat and the sorting office as an overflow), and got close up to the fence. From there, I could see into the back yard of the company in question. There didn't seem to be anyone around.

Not too good.

There was a large tank - about a metre high, a metre in diameter - which had a now-open opening on its top, maybe 20 cm across. Out of that opening was coming a solid pillar of the fumes which dissipated pretty quickly in the air.

I then went back to our reception, and we used Google Maps to zoom in to find the name of the company in question - Tru-lon Printed Circuits. Our receptionist Yelsel called their number, which was answered fairly quickly. Somewhat to our surprise, it turned out to be someone in Stevenage, which is a different town halfway down the county from us. It looks like the reason that nobody at Tru-lon was doing anything was that there was nobody there - the premises had been closed a while back. The person in Stevenage guessed from our description that the fumes were nitric acid, and said they'd send a chemist up to deal with it.

All well and good, but about 20 minutes after the initial pop, it was still smoking, even if nothing like as badly as it had been:

The smoking tank

So, we called the Fire Brigade.

About half an hour later, they were taking it quite seriously. We had a visitor telling us to stay indoors. At lkeast, that's what we think he said — it can be a tad difficult to understand someone speaking through a respirator:

New company dress code

And then, just before 18:00, the police arrived in force to evacuate us.

The road blocked off

That's an impressive array of vehicles there.

It appears that both roads into the industrial estate were closed off, and that even the route into town from the A505 was closed off.

So, this is my apology. If we'd not done anything, that tank would probably have continued fuming at a low level, without anyone being put out, until it finally evaporated. Instead, there was near gridlock in town. I can only think they react this strongly because they're prepared for problems at Johnson Matthey
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User: hairyears
Date: 2011-08-12 17:31 (UTC)
Subject: A dark and stormy Nitre

No, I think it was White Fuming Nitric Acid - WFNA. As delivered, this has no added nitrogen tetroxide (unlike Red Fuming Nitric Acid) and a maximum specified concentration of dissolved nitrogen oxides of 0.5%

It degrades over time, and the proportion of dissolved oxides goes up: you'll see light-brown fumes of NO2 at the surface - but not the cedar-wood reddish-brown fumes of Nitrogen tetroxide mixed with the dioxide. That's RFNA, not WFNA! That or very old, and very badly-stored old acid.

Needless to say, allowing NO2 fumes to build up is extremely dangerous - far more so than venting these toxic gases to the atmosphere! (Or through a filter, which is what you're actually supposed to do when storing it in bulk).

Among other issues, the pressure in an unvented container allows much more gas to dissolve; when the safety-valve eventually pops, the whole lot fizzes out of solution at once, creating a fog of Nitrogen dioxide gas and aerosolised Nitric Acid.

This is the yellowish smoke that you saw.

This smoke is scalding hot as well as toxic and corrosive: Nitric Acid reacts vigorously with water and the aerosol will heat up, even from the half-percent or so of water in the air.

The fire brigade had reason to be cautious: water could've caused a violent explosion, scattering corrosive liquids capable of starting fires. The source of the acid - the container - will have been dealt with by pumping-out into a safe receptacle and *maybe* neutralising the contents, very carefully and very slowly.

As for the affected area: eventually they'll have satisfied themselves that the gases have diffused to a degree that mitigates this danger, and sprinkled (not hosed!) the contaminated zone with water.

The company responsible (or irresponsible) are liable for cleanup costs, but the fines are surprisingly small - the vast majority of industrial accidents and pollution incidents, even ones that we would think of as serious, go to the magistrates and no further.

Edited at 2011-08-12 05:46 pm (UTC)
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The Bellinghman
User: bellinghman
Date: 2011-08-12 20:02 (UTC)
Subject: Re: A dark and stormy Nitre
I think you're probably right. Except there's a possibility that this might not have been terribly clean Nitric anyway since the company that had been there was a PCB company, and it's possible that this was used rather than fresh. If so, there will have been interesting copper salts in there too.
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