Four workers were killed and one of their colleagues suffered injuries in two blasts at a chemical factory in Khed taluka of Maharashtras Ratnagiri district on Saturday morning, a police official said. Around 40 other workers were rescued by the fire department staff and the police personnel following the blasts that triggered a blaze, he said. Two major blasts occurred inside a unit of the chemical factory around 9 am today. The workers injured in the incident were rushed to a government-run hospital, where four of them were declared dead. Another worker, who suffered critical injuries, is being treated, the police official from Ratnagiri said. The fire that erupted after the blasts has been brought under control and cooling operation is underway, he said. As per the preliminary investigation, a boiler at the factory exploded due to overheating. However, the exact cause of the incident is being ascertained, the official said.