The Beirut explosion is “unquestionably” one of the largest non-nuclear blasts in history, according to calculations by British engineering experts.

A team from the University of Sheffield has calculated the strength of the blast based on the videos and photographs that have emerged since Tuesday’s catastrophe.

They believe the explosion was the equivalent of 1000-1500 tonnes of TNT – a blast intensity that would support the belief that it was caused by the detonation of 2750 tonnes of ammonium nitrate fertiliser.

This is about a 10th of the intensity of the Hiroshima nuclear bomb but far bigger than any blast from a conventional weapon.

“There are simple rules of thumb relating the maximum expansion of the fireball to the size of the original explosive charge, and from some very approximate measurements from online video footage, we think the explosion is equivalent to something of the order of 1000 to 1500 tonnes of TNT,” Professor Andy Tyas, an expert on blast protection engineering at the university, said.

“We have also analysed video footage of the time delay between the detonation and the arrival of the shock wave at points several hundred metres from the explosion and these broadly agree with this size of charge.

“If correct, that would mean this explosion had perhaps 10 per cent of the intensity of the Hiroshima bomb.

“Whatever the precise charge size, this is unquestionably one of the largest non-nuclear explosions in history, far bigger than any conventional weapon.

“The effects of an event like this are catastrophic to people, infrastructure, economic livelihoods and to the environment.”

Professor Tyas’s team studies the mechanisms and magnitudes of blast wave loading from high explosive detonations, and their effects on structures.

“Industrial accidents of this scale caused by ammonium nitrate detonation have happened before, most notably at the Texas City port in 1947, where the detonation of a reported 2300 tonnes of ammonium nitrate produced a similar scale of damage to what we saw yesterday.”

Professor Tyas said the blast wave from a detonation of this size would produce lethal injuries and severe damage to unreinforced buildings for several hundred metres.

But he said the biggest danger in urban explosions was from flying glass. A blast explosion of this size was likely to cause extensive damage to glazing, and related injuries over a distance far beyond 1a kilometre.