Fireworks and ammonium nitrate thought to be the fuel responsible for the huge explosion

Fireworks and ammonium nitrate appear to have been the fuel that ignited a massive explosion that rocked Beirut, experts and videos of the blast suggest.

The scale of the damage – from the centre of the explosion at the port of Beirut to the windows blown out in buildings several miles away – resembles other blasts involving the chemical, which is commonly used as an agricultural fertiliser.

But the compound itself typically doesn’t detonate on its own and requires another ignition source. That is thought to have been a fire that engulfed what initially appeared to be fireworks that were stored at the port.

Online videos of the disaster’s initial moments show sparks and lights inside the smoke rising from the blaze, just prior to the massive blast, which indicates that fireworks were involved, said Boaz Hayoun, owner of the Tamar Group, an Israeli firm that works closely with the Israeli government on safety and certification issues involving explosives.

He said: “Before the big explosion, you can see in the centre of the fire, you can see sparks, you can hear sounds like popcorn and you can hear whistles.

“This is very specific behaviour of fireworks, the visuals, the sounds and the transformation from a slow burn to a massive explosion.”

Jeffrey Lewis, a missile expert at the Middlebury Institute of International Studies in Monterey, California, offered a similar assessment.

“It looks like an accident,” He added. “If you have a fire raging next to something explosive, and you don’t put it out, it blows up.”

The white cloud that accompanied the massive blast in the Lebanese capital appeared to be a condensation cloud, which are commonly seen in connection with massive explosions in humid conditions, following the shock waves of an explosion, Lewis said.

What initially started the fire at the port remains unclear. In comments made to a local TV station, Lebanese interior minister Mohammed Fahmi made no mention of ignited fireworks but said it appeared the blast was caused by the detonation of more than 2,750 tonnes of ammonium nitrate stored in a warehouse at the dock since it was confiscated from a cargo ship in 2013.

Based on the timeline and the size of the cargo, that ship could be the MV Rhosus. The ship was initially seized in Beirut in 2013 when it entered the port due to technical problems. It came from Georgia, and had been bound for Mozambique.

It remains unclear what conditions the ammonium nitrate had been stored in.