The incident occurred at Bismillah Space building located on Dimtimkar Road. Five workers entered a water tank to clean it but passed out inside while doing the job, said a fire official. The workers were rushed to JJ Hospital by the Mumbai Fire Brigade (MFB) for treatment where four of the five workers were declared dead by the doctors. An accidental death report (ADR) was registered and a probe has begun to find out lapses, if any, on the part of those who hired the five and whether safety protocols were adhered to, a JJ police station official said. A civic official identified the deceased as Hasipal Shaikh (19), Raja Shaikh, Jiaulla Shaikh and Imandu Shaikh. The fifth person, Purhan Shaikh is recuperating and is being treated at a nearby hospital, he said. The officials had put the death toll at five earlier, according to a civic official who said the incident occurred in the Nagpada area of Mumbai.