An official of the factory had been arrested on charges of not conforming to the required safety norms leading to the workers' death late last night, DCP (North) Siddaramppa told reporters here.
The post-mortem examination suggested that the workers died of suffocation. "We suspect that there were poisonous gases in the tank," Siddaramappa said.
He said first one worker had entered the tank to draw oil, a daily requirement for running machines. When he did not come out the second worker went into the tank to check if he was okay and then the third person followed.
All three were taken out unconscious and rushed to a hospital but declared brought dead, he said.
The workers had not been provided with masks and other safety equipment. "We booked factory manager Suresh for negligence and not conforming to safety measures," Siddaramappa said.
The factory owner was absconding and a hunt was on to nab him, he added.