The size of the Beirut port blast is estimated as being the equivalent of 200 to 300 tons of high explosives, according to experts who compared it to the 1986 10 tons Chernobyl disaster and fire, considered the world’s worst nuclear accident.

The comparisons came in a Reuters Graphics report in which George William Herbert, an adjunct professor at the Middlebury Institute of International Studies Center for Nonproliferation Studies and a missile and effects consultant, used two methods to estimate the yield of the explosion.

According to Herbert, the first method was done by using visual evidence of the blast itself along with damage assessments. The second calculation was based on the amount of ammonium nitrate reportedly at the source of the explosion.

Both techniques estimate the yield as a few hundred tons of TNT equivalent, with the overlap being 200 to 300, Herbert told Reuters.

Reuters also spoke to an Israeli analyst on Thursday who said that seismological data suggests that six blasts preceded the main explosion. According to the analyst, the last of the six smaller blasts resulted in the combustion of fireworks that set off a warehouse full of ammonium nitrate.

“I cannot say categorically what caused this, but I can say these blasts were at the same location,” the Israeli analyst told Reuters.

Roland Alford, managing director of Alford Technologies, told Reuters that the Beirut explosion should be scaled down from a nuclear bomb rather than up from a conventional bomb.

“This is probably up there among the biggest non-nuclear explosions of all time,” said the managing director of Alford Technologies, a British company that specializes in disposal of explosive ordnance.