At least three people sustained serious injuries at the Soprema plant in France, France Info reported.
The factory personnel had extinguished the fire, which reportedly followed the blast, on their own before fire brigades arrived, according to the local prefecture.
All staffers were shortly evacuated, and a vast security zone was set up around the plant. According to television channel BFM, the incident occurred during a scheduled maintenance check at the storage facility of one of the chemical units earlier in the day. The plant, which manufactures a variety of sealing materials, is reportedly on the list of the most dangerous chemical factories.
Investigation has been launched into the case.
Soprema, which was founded in 1908, has overall 59 manufacturing plants including 22 waterproofing factories, 19 insulation factories, and 1 geotextile plant.
Soprema Group currently employs 6,892 people in its 51 manufacturing plants, with 15 being located in France, as well as 60 operating subsidiaries and over 4.000 distributors with sales up to € 2.32 billion, according to 2016 estimates.