Kolkata, Dec 28 (Reporter) At least three persons, including a woman, were grievously injured in an explosion at a firecracker factory in West Bengal's South 24 Parganas district, official sources said on Saturday. The roof of the factory-cum-house burned and collapsed following the explosion in which the owner- PIintu Mondal- received almost cent percent burn injuries, sources added. All three have been admitted to the MR Bangur Hospital in south Kolkata. The explosion happened this noon at the factory located at Haral under Baruipur Police station. It was not immediately known how the explosion happened.Forensic department officials visited the scene of the explosion to ascertain the cause of the blast and the kind of explosives, sources added...////...