Thursday 11 July 2013


If you're expecting more on More's favoring of hair-shirts and the whip, I refer you to the original post, which made a peripheral mention of flagellation. This is rather an development of the fun I had talking about the explosive power of TNT. My research there alerted me to the difference between detonation and deflagration.  I'm not sure I really understand why the distinction is important, but it hinges on whether the explosion propagates supersonically (detonation) or slower than the speed of sound.  But it did explain why you shouldn't pour water on a chip-pan fire.  What happens there (a textbook example of deflagration) is that the boiling point of water is much less than the hot oil or tallow in the pan.  A mole (18g - 1 tbs in kitchen-speak) of water vaporises and, because of the ideal gas law, instantly occupies 22.7 litres of space.  In the heat of the moment, you're much more likely to cast thereto a 300g cupful of water which will instantly fill a space about twice the size of our cooker with a potent mix of steam and flaming oil.  Goodbye eyebrows (at least).

Today is the 35th anniversary of the Los Alfaques disaster, near Tarragona in Spain.  There, an overloaded road-tanker containing 22 tons of propylene crashed beside a campsite crowded with near-naked tourists.  The liquid fuel started to vaporise from the ruptured fuel tank.  22 tons is conveniently close to half a million moles of propylene (MolWt 42) which as vapour would fill a couple of football fields to a depth of 1 metre (propane is heavier than air).  This didn't happen at Los Alfaques because, before the tank was half empty, the edge of the vapour cloud reached the campsite's disco where it ignited killing everyone inside.  The flame front deflagrated back to the tanker which exploded in a spectacular BLEVE (boiling liquid expanding vapor explosion) killing dozens more people out on the roadway.  They made a film of it, Tarragona - Ein Paradies in Flammen if you like that sort of thing.

The toll of injury and fatalities was much greater because lots of people, dressed in swimming togs, went to investigate the strange mist that suddenly appeared in the middle of the day.  It turned out that the road-tanker had been used for transporting a variety of other liquids, including high corrosive anhydrous ammonia, before it started on the propylene run.  It is likely that the overloaded, overpressurised tank, travelling through Spain in July (hot) failed at a microscopic crack eaten by the ammonia years previously.  There were not, understandably, many eye-witnesses.

I was travelling to work at The Institute on 18th April when I heard reports on the wireless of the explosion of ammonium nitrate at West, Texas.  I was shocked at the time by an extraordinary editorial decision made by the Irish news team.  It's taken nearly 3 months for me to calm down enough to talk about it.  In the scrabble for here-and-now reportage, they thought the plain people of Ireland needed to hear a clip of a small girl crying "Daddy, daddy, I can't hear".  Apparently, her father had thought it was a smart idea to take his daughter to see the fire at the West Fertilizer Company and had caught the explosion on video and in both their faces.  Sometimes, when you get woken up to see some amazing raree show, it's better to turn over, put your head under the pillow and go back to sleep.  The Day of the Triffids is a whole book extolling the virtues of such  a policy.

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