Six people were treated for chemical inhalation yesterday after four packets containing chemical residue self-ignited in a bin outside a factory in Mrieħel, emitting toxic fumes.

The hazardous materials (Hazmat) team of the Civil Protection Department rushed on site at about 10.15am after the four packets with magnesium sulphide residue caught fire near the Vernon Foods plant.

As water was used in an attempt to put out the fire, the chemical reacted to form a highly toxic gas known as phosgene.

The police evacuated the area as Hazmat team members worked to seal the items, which were then taken away to be safely disposed of.

Two employees and four CPD members were taken to hospital as a precautionary measure. They were released later in the day.

Phosgene gas may appear colourless or as a white to pale yellow cloud. At low concentrations, it has a pleasant odour of newly-mown hay or green corn but its odour may not be noticed by all people exposed. At high concentrations, the odour may be strong and unpleasant.

The gas was used extensively during World War I as a choking agent. Among the chemicals used in the war, phosgene was responsible for the large majority of deaths.