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The mixture is affected by humidity because ammonium nitrate is highly hygroscopic. Ammonal's ease of detonation depends on fuel and oxidizer ratios, 95:5 ammonium nitrate and aluminum being fairly sensitive, however not very oxygen balanced. Even copper metal traces are known to sensitize bulk amounts of ammonium nitrate and further increase danger of spontaneous detonation during a fire, most likely due to the formation of tetraammines. More oxygen balanced mixtures are not easily detonated, requiring a fairly substantial shock, though it remains more sensitive than trinitrotoluene and C-4.
The detonation velocity of ammonal is approximately 4,400 metres per second or 9,842 miles per hour.
From early 1916, the British Army employed ammonal for their mines during World War I, starting with the Hawthorn Ridge mine during the Battle of the Somme. Three of the mines used at the Battle of Messines, which were exploded at the start of the Third Battle of Ypres (a.k.a. Battle of Passchendaele), contained 30,000 lbs (over 13.6 metric tons) of ammonal. A fourth contained 20,000 lbs (over 9 metric tonnes). The British Army detonated 19 ammonal mines under the German lines, killing 10,000 in the deadliest non-nuclear man-made explosion in history.
Not all of the mines that had been laid at Messines were detonated. Two of the original 21 mines were not ignited because they were outside the area of the offensive. On 17 July 1955, a lightning strike set off one of the remaining mines. There were no human casualties, but one cow was killed. The 21st mine is believed to have been found, but no attempt has been made to remove it. It is possible that the one unexploded mine was dismantled, because German tunnellers were coming too close to the chamber.
Ammonal used for military mining purposes was generally contained within metal cans or rubberised bags to prevent moisture ingress problems. The composition of ammonal used at Messines was 65% ammonium nitrate, 17% aluminum, 15% trinitrotoluene (TNT), and 3% charcoal. Ammonal remains in use as an industrial explosive. Typically, it is used for quarrying or mining purposes.
- ammonium nitrate 58.6%
- aluminum powder 21%
- charcoal 2.4%
- TNT 18%
- Tweedie, N. (2004-01-12). "Farmer who is sitting on a bomb". The Daily Telegraph. Retrieved 2010-05-17.
- Brown, G. I. (1998). The Big Bang: A History of Explosives. Sutton Publishing. p. 163. ISBN 0-7509-1878-0.
- Chamberlain, J. S. (1921). A Textbook of Organic Chemistry. Philadelphia: P. Blankiston's Son & Co. p. 534. OCLC 245530036. Retrieved 2010-05-17.
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