The huge explosion in Beirut which killed at least 135 people is "unquestionably" one of the largest non-nuclear blasts in history , experts have said.
A team of engineering experts from the University of Sheffield calculated the strength of the blast, which injured around 5,000 people, based on the videos and photos which have since emerged.
They say the explosion was the equivalent of 1,000 to 1,500 tonnes of TNT - a blast intensity which would support the belief that it was caused by a fire leading to the detonation of 2,750 tonnes of ammonium nitrate fertiliser.
This is about a tenth of the intensity of the Hiroshima nuclear bomb but far bigger than any blast from a conventional weapon, they said.
Lebanon: Beirut explosion aftermath - In pictures
Professor Andy Tyas, an expert on blast protection engineering at the university, said: “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 1,000-1,500 tonnes of TNT.
“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% 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.”
Prof Tyas’s team studies the mechanisms and magnitudes of blast wave loading from high explosive detonations and their effects on structures.
He said: “If the figure of around 1,000 to 1,500 tonnes is correct, it would match with reports that the explosion was caused by a fire leading to the detonation of 2,750 tonnes of ammonium nitrate fertiliser.
“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 2,300 tonnes of ammonium nitrate produced a similar scale of damage to what we saw yesterday.”
Prof 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 that the biggest danger in urban explosions is from flying glass, and a blast explosion of this size would be likely to cause extensive damage to glazing and related injuries over a distance far beyond 1km.
The Blast & Impact Dynamics Research Group at the University of Sheffield have been explaining their evolving analysis of the blast on their @SheffieldBlast Twitter feed.
Additional reporting by Press Association.
