[Enthalpy]

New claims about the explosion of the AZF plant in Toulouse in 2001.

One safety consultant company, Preventique, suggests links with a plant of rocket propellants 600m away:
http://www.preventique.org/content/azf-ou-snpe
this theory was relayed by the general newspaper Sud Ouest, later by others:
http://www.sudouest.fr/2012/08/29/azf-la-these-officiel-le-remise-en-cause-806412-4697.php

You may believe or not that a leak of UDMH at SNPE's plant cought fire and detonated the ammonitrate. Preventique even suggests the detonation passed first through unexplosed WWII bombs. But I feel the sheer context disturbing:

- UDMH (10t!) is said to have leaked, and neighbours describe a strong smell of fish and amine; the odour limit is 6 to 14ppm.
- UDMH is very volatile: 145mb @+20°C, and explosion limits are 3 to 95%. But I haven't read of a direct flame over the 600m distance... Preventique hence seeks an indirect propagation, for which I don't imagine a delay. UDMH vapour catching fire at the ammonitrate plant is less improbable.
- Neighbours tell of two successive explosions, and also of sparks at power lines, which some tests of EMP bombs built at the UDMH plant could explain.

Whatever credible this theory is (officially preferred theories are no better!) at least it points that:
UDMH was produced in ton amounts in a city, which is foolish.

The IDLH concentration (Immediately Dangerous for Life or Health) of UDMH in air is 15ppm. Compare with 3ppm for Methyl Isocyanate of which 30t leaked at Bhopal. In space ports, when they still have to use UDMH, they evacuate the personnel, and propellant workers use a hermetic suit with autonomous air. And as UDMH is a carcinogen, its allowable concentration in air is 0.01ppm. Many victims at Toulouse have neurological troubles, said to result from the pressure wave and psychological pain, but UDMH is also neurotoxic.

Was UDMH voluntarily ignited to avoid the poison danger? Not really necessary, as the thing is so flammable.

To explain why ammonitrate was produced in a city, they told the plant was built in 1920 as the city was far away, but the UDMH plant was only 30 years old. And anyway, it doesn't tell why ammonitrate was stored in many-tons amount instead of separating small amounts in explosion-proof grooves, as must be done with any explosive. Except that law did, and still does, define ammonitrate as a fertilizer only.