This combination of pictures created with footage filmed from an office building at the moment a massive explosion rocked Beirut on August 4, 2020. Photos: Gaby Salem / AFP

BEIRUT – Lebanese authorities say a mammoth store of ammonium nitrate caused an explosion of kiloton magnitude that ripped through the Lebanese capital on Tuesday, leaving more than 100 people dead and thousands wounded.

The storage in a single warehouse of 2,750 metric tons of ammonium nitrate, more than a thousand times the amount deployed in the Oklahoma City bombing of 1995, has sparked fierce scrutiny about why authorities allowed the notoriously weaponizable fertilizer to be kept for so long.

Lebanon’s top customs official Badri Daher on Wednesday defended his record, saying he had made six requests to the Lebanese judiciary to order the material re-exported since its confiscation seven years ago.

“We will leave it to the relevant investigators to determine the reason” why requests for re-export were not facilitated, Daher told broadcaster LBCI.

Beirut Port has been saddled with the stock since 2013, when a Moldovan-flagged tanker en route from Georgia to Mozambique made an emergency port of call. The Rhosus tanker was found to have severe deficiencies and was banned from continuing its journey, its crew left temporarily stranded and its owner nonresponsive.

Customs officials were eventually compelled about a year later to remove the ammonium nitrate from the ship and transfer it to the warehouse where it has been held since.

Tuesday’s explosions leveled almost the entire port, killing and wounding those in their vicinity, and destroying containers full of critical imports in a country in the midst of a financial crisis.

“It is unacceptable that a shipment of 2,750 tonnes of ammonium nitrate has been present for six years in a warehouse, without taking preventive measures,” Prime Minister Hassan Diab told a Defense Council meeting in the wake of the catastrophe, a spokesman said.

Internal Security chief Major General Abbas Ibrahim, surveying the port hours earlier, said initial reports suggested a highly explosive material, confiscated “years earlier” had ignited.

The critical question observers are asking today is how.

A wounded woman helps another injured person get into the backseat of a car in Beirut following a twin explosion at the port of Lebanon’s capital on August 4, 2020. Photo: Marwan Tahtah / AFP
Rescuers and civil defence gather at Beirut port’s silo on August 5, 2020 in the aftermath of a massive explosion in the Lebanese capital. – Rescuers searched for survivors in Beirut after a cataclysmic explosion at the port sowed devastation across entire neighbourhoods, killing more than 100 people, wounding thousands and plunging Lebanon deeper into crisis. The blast, which appeared to have been caused by a fire igniting 2,750 tonnes of ammonium nitrate left unsecured in a warehouse, was felt as far away as Cyprus, some 150 miles (240 kilometres) to the northwest. (Photo by JOSEPH EID / AFP)

Not easily combustible

Internationally, there are strict rules about where ammonium nitrate can be stored, specifically that it must be kept away from fuels and sources of heat to prevent accidents.

In the United States, regulations over ammonium nitrate were tightened significantly after the Oklahoma City bombing of a federal building in which 168 people died. Under the Chemical Facility Anti-Terrorism Standards, facilities that store more than 900 kilograms of ammonium nitrate are subject to inspections.

Moeen Hamza, who heads Lebanon’s Council for Scientific Research, on Tuesday night accused Beirut port authorities of pure negligence, telling broadcaster Al-Jadeed that such a massive store should have been monitored around the clock.

Yet ammonium nitrate is not easily set off.

A view of the damage after a fire at a warehouse with explosives at the Port of Beirut led to massive blasts in Beirut, Lebanon on August 5, 2020. Photo: Houssam Shbaro/Anadolu Agency via AFP Forum

Under normal storage conditions and without extremely high heat it is difficult to ignite ammonium nitrate in any quantity, according to Jimmie Oxley, a chemistry professor at the University of Rhode Island.

Ammonium nitrate is an oxidizer, which intensifies combustion and allows other substances to ignite more readily, but is not itself very combustible.

This makes it a preferred tool for those wanting to carry out explosions without the risk of getting hurt in the process.

When combined with fuel oils, ammonium nitrate creates a potent explosive widely used by the mining and construction industries, but also by terrorist and insurgent groups like the Taliban for improvised explosives.

Trump flags bomb

Experts say the detonation of the ammonium nitrate in Beirut would have required an initial explosion, the cause of which remains under investigation.

Videos of the incident filmed from various angles show an initial blast that sends up a plume of smoke, followed by a second, mega-blast that sends a cloud billowing far above the city skyline and into the harbor.

US President Donald Trump on Wednesday walked back a previous remark in which he’s suggested the explosion had been intentional.

Tuesday had told reporters his military brass believed the explosions to have been caused by a “bomb of some kind.”

“This was not some kind of a manufacturing explosion type of event. It seems to be, according to them – they would know better than I would – but they seem to think it was an attack,” he’d said.

But on Wednesday he backtracked, saying, “I can tell you whatever happened, it’s terrible. But they don’t really know what it is. Nobody knows yet.”

“How can you say accident?” Trump continued in his Wednesday comments. “Somebody … left some terrible explosive devices and things around perhaps. Perhaps it was that. Perhaps it was an attack. I don’t think anybody can say right now. I’ve heard it both ways.”

Daher and others have suggested that a stock of fireworks set off the first blast. Investigations are still in progress, and it is not yet clear if and why such a close proximity was allowed, leaving questions over the official narrative. Other reports carried by local media say a welder fixing a warehouse ceiling may have set off the chain reaction.

An aerial view shows the massive damage done to Beirut port’s grain silos (C) and the area around it on August 5, 2020, one day after a mega-blast tore through the harbor in the heart of the Lebanese capital. Photo: AFP

But with Lebanese having witnessed decades of corruption and incompetence by sectarian political elites, early speculation that Tuesday’s blast was an attack on a Hezbollah weapons depot appears to be giving way to consensus that gross criminal negligence was to blame.

Against the backdrop of recent tensions with Hezbollah, Israeli political sources told Haaretz the country had nothing to do with the Beirut blasts. Hezbollah leader Hassan Nasrallah, who was scheduled to speak on Wednesday, has postponed his address.

“What happened today will not pass without accountability,” Diab promised in a late night address to the public, even as bodies were still being dug from the rubble of buildings.

Alison T Meuse is the Asia Times Middle East editor and correspondent.