Garden Grove chemical threat: 40000 evacuated as overheated tank faces explosion

Here's some interesting material.

There are established software approaches aimed at modeling potential runaway polymerization for the times that polymer is intentionally being made from a monomer:

https://iomosaic.com/docs/default-source/papers/polymerizati...

https://www.linkedin.com/pulse/modeling-runaway-scenario-but...

That's the same Butyl Acrylate incident reviewed by the same safety contractor, but published differently in both links. Keep in mind this Butyl Acrylate explosion was a pressure vessel reactor, rated for many atmospheres of duty before physical failure.

It appears the MMA tank in question at Garden Grove is not a reactor, but a more common industrial storage tank. Much more sizable of a tank than an expected batch reactor would be, but "mere" storage is not supposed to be at any significant pressure. So the tank walls are not usually any more thickly built than ordinary gasoline tanks. IOW if the tank were not properly vented to the atmosphere, it would not be expected to require as much pressure before rupture, compared to an actual reactor. And that may or may not affect the theoretical physical blast radius and/or chemical damage radius. Considering both the amount of chemical and the force differences.

In monomer storage, all effort necessary is supposed to be focused on prevention of polymerization. Now here is a paper from 1994 where some lab work was done to give better ideas about when runaway is already occurring and needs to be halted or at least curtailed:

https://www.icheme.org/media/10375/xii-paper-40.pdf

Disclosure: I'm one who developed a number of techniques for more reliably measuring the inhibitor content of monomers, and with MMA still maintain two instruments when no more than one instrument has ever been needed at one time. Needless to say, this is an important test and to provide routine one hour turn-around on a 24/7 basis you've just got to have a backup.

In addition to the common MEHQ inhibitor, we are also seeing Topanol (dimethyl-tert-butylphenol) in established use for MMA. The alternative inhibitor phenothiazine is apparently not very common in our area.

One problem is that the inhibitors are solids or syrups which don't really evaporate. However they are very effective inhibitors when dissolved in the liquid monomer at quite low concentrations. But as the monomer slightly vaporizes to an extent while being contained in the storage tank, these vapors contain no inhibitor. And these are the vapors that condense on the walls and roof of the tank which can end up polymerizing on their own, sometimes forming "stalactites" or gumming up the vapor-recovery atmospheric ventilation arrangement. If that was badly clogged it could be one reason causing the tank to bulge which does sound pretty ugly.

All these industrial acrylate monomers are some nasty smellers, but the lighter ones like methyl acrylate or MMA do evaporate fast like an alcohol or acetone. With good ventilation the vapors dissipate just as quick. More toxic though and just as flammable to boot. OTOH butyl acrylate is heavier, so it dries up and goes away much slower, fondly known as "Brutal" Acrylate on the tank farm or by the few lab workers who are familiar with it.

They all basically make you say "ack" when you smell it, and you can pick it up miles further away than almost anything else.