Manufacturing News

Fire in anhydrous ammonia tank may have caused Texas blast

Experts analysing the explosion at the fertiliser plant in Texas point to the dangerous nature of the chemicals the plant was producing.

Anhydrous ammonia is the base for much of the fertilizer types produced globally. Although it is a cheap and effective compound, handling and processing anhydrous ammonia and its affiliated chemical, ammonium nitrate, is not without risk.

Even the instruments in such a plant need to be carefully chosen. For example, pressure gauges and fittings cannot be made of copper, zinc or alloys such as brass.

Australia has had its share of disasters with this chemical, including the one in 1974 in Taroom, Queensland where two tonnes of ammonium nitrate on a truck caught fire and exploded, killing three people.

According to a report in The Guardian, since 1921, at least 17 unintended explosions of ammonium nitrate including casualties have been recorded.

Anhydrous ammonia is typically stored in liquid form in high pressure tanks. A rise in external temperature causes the liquid to expand thus putting the tank structure under pressure.

A leak allows the liquid to convert immediately to gas which causes serious chemical burns to those who come in contact.

Workplace Standards Tasmania issued this warning: "Although relatively stable in isolation and when handled and stored carefully, ammonium nitrate will support combustion initiated in another material.

"Its oxidising quality will intensify a fire, even in the absence of air. When subjected to sufficient heat, ammonium nitrate becomes molten, extremely sensitive to impact, and will detonate readily. Ammonium nitrate does not need to be mixed with fuel oil to detonate."

In Texas, around 15 buildings in the vicinty of the plant have been demolished and some 50 homes heavily damaged. At the time of writing, two people were reported dead and 60 injured.

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