Ammonium nitrate blast generated the power of a small nuclear bomb

The 2,750 tonnes of ammonium nitrate responsible for damaging about half of Beirut on Tuesday exploded with the power of a small nuclear weapon, an explosives expert in the UK said.

The blast had 10 per cent of the explosive yield of the atomic bomb dropped on Hiroshima 75 years ago on Thursday.

At least 145 people died in the Beirut explosion, with more than 5,000 injured and about 100 missing.

Prof Andrew Tyas, an expert in blast protection engineering at the University of Sheffield, said tens of thousands would have been killed had the explosion occurred 400 metres closer to the city centre.

His team spent hours on Google maps examining the size of the explosion and the damage it caused.

“This has the equivalent yield to something that’s on the scale of the smallest tactical nuclear weapon,” Prof Tyas said.

He said it took time for him to fully comprehend the magnitude of the disaster.

“At first, I was almost unable to process the scale of the explosion. It was almost as if I didn’t want to believe it was quite on that scale,” he said.

“Then we started doing the numbers and it was very sobering, realising that this was bigger than most things that have ever happened in an urban environment before.”

Prof Tyas said the research his team carried out on the explosion convinced him that it was not the result of an attack by extremists.

A blast set off by terrorists would be the equivalent of one or two tonnes of TNT going off. The port explosion was equivalent to 1,500 tonnes of TNT.

“You’re looking at something that’s 1,000 times bigger than what would normally be classed as a very, very large, devastating terrorist attack,” he said.

“We realised very quickly that there’s no way this could have been a conventional weapon attack.

“It’s an order of magnitude bigger than anything you’d expect to see from a normal terrorist explosive attack. So the obvious thing that was pointing towards was some sort of industrial accident.”

There are concerns that residents of Beirut could suffer respiratory problems from the toxic cloud the explosion produced, which was similar to one created by a chemical explosion in Tianjin, China, five years ago.

“If it rains into a cloud like the Tianjin explosion did, you can get things like nitric acid condensing out of it,” Prof Tyas said.

Lebanon’s main grain silo, which held up to 120,000 tonnes of grain, was next to the warehouse where the ammonium nitrate was stored.

Prof Tyas said people often believed major structures acted as a defence against explosions, but the grain silo was unlikely to have saved any lives in Beirut.

“Instinctively, you would think it helped protect anyone who was in that immediate region, but the problem is just the magnitude of the explosion is so big,” he said.

“Even an 80 or 90 per cent reduction in the blast loading is still likely to end up in pressures that are fatal to anybody around there.”

Prof Tyas said he believed the explosion could have been the result of a fire, either from a dropped cigarette or electrical fault.

He said that could have been enough to ignite the chemical stockpile.

Prof Tyas that to prevent future catastrophes, the authorities should ensure that explosive substances were stored far from urban areas.