Investigators are focusing on what caused the fire that preceded Monday's devastating explosion at the Ta' Lourdes fireworks factory near Salini.

The site remains closed to the public and under police guard as investigations continue into the blast, which sent shockwaves across several parts of Malta. Police forensic experts and members of the Armed Forces of Malta's explosives unit are carrying out extensive examinations, while a magisterial inquiry led by Magistrate Joe Mifsud is also underway.

According to TVM, investigators are collecting security camera footage from nearby properties, assessing reports of damage submitted by residents, and have completed a three-dimensional mapping of the area. A crucial video reportedly shows black smoke and flames before a powerful explosion, followed by a series of secondary blasts.

Professor Alfred Vella, a chemist, told TVM that the sequence of events suggests that investigators must first determine the source of the fire before establishing why the explosions occurred. He noted that the thick black smoke seen before the blast was significant because it indicated the burning of materials low in oxygen content, such as plastics, charcoal-based substances, or similar products, rather than vegetation, paper or cardboard.

Vella said the prolonged fire before the explosion suggested that an explosive mixture was not necessarily the first material to ignite.

He noted that several possibilities remain under consideration, including waste materials from fireworks experiments or changes caused by humidity affecting exposed substances.

Vella also described how the explosion caused widespread damage. Flying stones acted as "secondary missiles", while the pressure wave and hot gases generated by the blast contributed to the destruction reported in surrounding areas.

He also raised concerns about possible contamination of crops, animal feed and livestock. Unburnt residues from fireworks compounds may have been dispersed across nearby agricultural land, he said, making scientific testing essential before decisions are taken on whether food or feed products can be safely used.

The Food Safety Authority confirmed it has deployed officials to assess the impact on food, feed, livestock and agricultural operations. It said precautionary measures are being taken to ensure that any potentially contaminated products do not enter the food chain, while inspections, risk assessments and sampling will continue in the coming days.

The Ta' Lourdes facility belongs to the 11 February Pyrotechnic Association of St John, although pyrotechnicians involved in other village feasts also operate from the site.