Thursday 30 April 2009

Enormous Blunders (Part I)

This is the first of a series of really stupid acts. The only appropriate heading for these acts is 'Enormous Blunders'.

The Oppau disaster

Ammonium nitrate is a well-known explosive commonly used in a 2/3 mix with TNT in aerial bombs. World War II was fought with ammonium nitrate explosives. If the quantity level is 10,000,000 pounds (4,800 tonnes), it will create an explosion comparable to that caused by a nuclear bomb. Thus, it was known to be extremely dangerous in large quantities, primarily due to its supporting oxidation. This was the chemical that was part of the fertilizer that was used by Timothy McViegh to destroy the federal building in Oklahoma City in 1995. His truck was filled with roughly 5,000 pounds (2.5 tons---2,300 kg) of ammonium nitrate, an agricultural fertilizer, and nitromethane, a highly volatile motor-racing fuel-a mixture also known as Kinepak or ANFO (ammonium nitrate/fuel oil). The explosion was felt for miles and 168 people were killed. It follows that fertilizer that contains quantities of ammonium nitrate must not be close to anything that will explode.

The city of Oppau is in Germany and in that city is a BASF plant that began producing ammonium sulfate in 1911. However, during World War I when Germany was unable to obtain the necessary sulfur, it began to produce ammonium nitrate as well.

Compared to ammonium sulfate, ammonium nitrate is strongly hygroscopic, so the mixture of ammonium sulfate and nitrate clogged together under the pressure of its own weight, turning it into a plaster-like substance in a silo that was 20 metres in height. The workers needed to use pickaxes to get it out, a problematic situation because they could not enter the silo and risk being buried in the collapsing fertilizer.

Strangely enough, they used small charges of dynamite to loosen the mixture. It is beyond me as to why that the mixture didn’t explode when the small charges of dynamite were being used. The procedure was tried experimentally and was considered safe. It was not known at the time that ammonium nitrate was an explosive substance and considering the fact that the small charges of dynamite hadn’t set off the ammonium nitrate, I can understand why they thought it was safe to separate the mixture this way. Because nothing extraordinary happened during an estimated 20,000 firings, I have to presume that the mixture had a lower concentration of ammonium nitrate during those times and that is why the ammonium nitrate in the fertilizer didn’t explode.

On September 21st, 1921, there was a higher concentration of ammonium nitrate in the mixture and the silo then had 450 tonnes of the new mixture in it. There was a further 4,500 tonnes of fertilizer stored in the warehouse nearby.

The employees decided that because the mixture was still hard to get out with pick axes, they would use dynamite again. You know what is next, don’t you.

The silo exploded. All of the employees nearby vanished in the explosion. In fact, the bodies of 300 of the employees were never found.

The explosion was estimated to be equivalent to between 1 and 2 kilotonnes of TNT and was heard as a loud bang in Munich, more than 300 kilometres away. The pressure wave ripped roofs off of houses up to 25 kilometres away and destroyed windows even farther away. In Heidelberg (30 kilometres from Oppau), traffic was stopped by the mass of broken glass on the streets.

Approximately 80 percent of all the houses in Oppau were destroyed, leaving 6,500 homeless. At ground zero, a 90 metre by 125 metre crater and 19 metre deep, was created. Damages were estimated at $1.7 million ($21 million in 2007 US dollars)

There were 565 bodies found in the town and the factory and about 2,000 people were injured, many seriously.

It was fortunate indeed that the blast didn’t cause the rest of the ammonium nitrate-laden fertilizer in the nearby warehouse to explode. The damage and death toll would have been much greater if it had exploded.

During the Second World War, the area was severely bombed by the Allies because of the large chemical plant in Oppau thereby causing many more deaths but after the war, the town and chemical plant was rebuilt and Oppau became a small city of 10,000 by the end of the last century.

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