Locals in the area staged a protest after the incident, saying a similar accident in the future could turn out to be more devastating.
Forty-five workers were injured in the incident, Shahaji Umap, Deputy Commissioner of Police (Zone-VI), said.
After preliminary treatment at the BPCL's first aid centre, 22 of them were allowed to go home, while others were shifted to a nearby hospital in Chembur, he said.
Nine fire tenders, two foam tenders and two jumbo tankers were pressed into service to douse the blaze.
Along with the Fire Brigade, the refinery's own fire-fighting team, HPCL, Bhabha Atomic Research Centre, RCF and Mazgaon Dock fire brigades were also engaged, an official of the Disaster Control Room of the Brihanmumbai Municipal Corporation said.
The incident took place in the "Compressor shed of Hydrocracker plant", as per the company's statement.
"The hydrocracker unit has been safely shut down while the other units are normal. No product shortage is envisaged on account of the fire," the company said late in the evening.
Fire Brigade Chief P S Rahangdale said the fire fighting was made difficult by heat and built-up pressure inside the plant.
According to Santosh Aadhar, a local resident, a "massive" explosion was heard in the surrounding area.
"Its tremors shook windows of our building which is 500 metres away from the refinery," Aadhar told reporters.
People living in the vicinity gathered at the refinery's gate, shouting slogans and demanding that they be relocated from the area.
Hundreds of families displaced for various government projects or due to slum demolitions have been resettled in Mahul village.
"Had the boiler exploded near our building, we would have been reduced to ashes," said Puja Waghmare, a local resident.
Reshma Chavan, another woman, said, "Today's explosion shattered the window panes in our building. We were lucky that the plant where it happened is farther from our building. Can anyone guarantee that such incident will not take place in future?" she asked.
Shivraj Pandit, convenor of Chembur Welfare Brigade, a local outfit, said air pollution in the area is a major concern, and the government agencies were neglecting it.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)