Watch: New video shows fire broke out before massive factory blast

A newly emerged video of Monday morning's massive fireworks factory explosion shows smoke billowing from a fire at the site moments before three rapid blasts erupted in quick succession. Each explosion grew progressively larger, culminating in a massive final detonation that sent a huge plume hundreds of feet into the air and generated a shockwave felt across Malta.

Times of Malta spoke to chemical expert, professor Alfred Vella, who said that while the full cause of the blast remains unknown, the new footage offers a critical clue as to what might have set off the explosions.

The presence of a fire before the explosion indicates the disaster might have been triggered by an active blaze on-site, he said, rather than a minor initial blast.

Such a minor blast is the energy which typically causes most fireworks factory incidents.

“Investigators will now likely focus on establishing what caused the fire to get to the bottom of the incident,” he said.

The Lourdes fireworks factory between Salini and Naxxar blew up in the most sensational way early in the morning on Monday, blasting out window panes and doorways in nearby neighbourhoods and sending a thick plume of smoke into the air.

There were only minor injuries and police said all people who work on site and neighbours were accounted for. This means it is likely that nobody was on site when the explosion happened, which cuts out the most common cause for pyrotechnic accidents: human error during active mixing or handling.

The video, which is doing the rounds on social media, captures a rapid, terrifying chain reaction. At first, only thick black smoke is visible, with no explosions taking place.

Then, a large blast suddenly erupts from the smoke, followed a second later by an even bigger explosion that sends colourful display fireworks shooting out into the air.

About two seconds after that, a final, colossal explosion tears through the complex, shooting hundreds of feet into the sky and creating the massive plume of grey smoke and fire that gripped the country's attention on social media.

What could it have been?

Asked what could have sparked the fire if no one was working inside the factory, Vella outlined several possibilities.

If investigators find that people were working on site in the hours before the explosion or over the weekend, the cause could still be down to some human error, he said. But even if there was no human intervention, spontaneous eruptions like that one are not a surprise when it comes to fireworks.

Pyrotechnic materials are inherently unstable chemical compounds, he said, and when left entirely alone, they are still subject to environmental, chemical, and physical phenomena that could trigger a spontaneous mass detonation.

“These mixtures are extremely sensitive and the tiniest energy input that can cause them to ignite, will probably set them off," he said.

"Sometimes that could happen from a chemical reaction from raindrops seeping from the ceiling after rainfall falling on the wrong material. A spark of static electricity and humidity can also have the same effect. And so can fine dust particles floating in the air, delivering vegetal dry matter from surrounding fields or from different materials just sitting too close together in the factory.”

What was in the blast?

The law sets out legal limits for the storage of firework materials. Factories can only lawfully store up to 1,000 kilograms of potassium chlorate and 3,200 kilograms of potassium nitrate, but there is one other chemical that is not legally regulated and which Vella believes was likely involved in the explosions.

“Chlorate and nitrate are the controlled oxidising agents which the local legislation considers. There is another important oxidising agent called potassium perchlorate, and this is not controlled,” he said. 

“We can safely assume that the explosion involved a considerable amount of this material. The size of the crater would give an indication to the trained eye of the quantity of explosive involved in the blast.”

Vella also said it is quite common for such incidents to unfold in a series of explosions, and not just one blast. The successive explosions after the first one are known as 'sympathetic explosions', and they are triggered by the fire or heat from the first blast.

This is why firework factories are specifically built with thick, reinforced walls and separate rooms to prevent a fire in one area from spreading to another.

But it was still very early to attempt to pin down the real cause behind Monday’s blast, he said. These incidents are usually complex and are triggered by a myriad of factors that can only be determined through detailed examinations on site.

Investigations are ongoing.