The men had gone to attend a fire call at 10.15 pm yesterday when the tragedy took place, said an officer from Delhi Fire Services.
They were working to control the blaze when there was a cylinder blast.
A tin shed on the second floor of the factory collapsed due to the explosion and firemen Vijender Pal (52) and Sunil Kumar (50) got trapped under the debris.
The injured firemen were rushed to Jeevan Mala Hospital and later shifted to Sir Ganga Ram Hospital.
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While Pal died during treatment, Singh and Kumar were stated to be in stable condition.
Singh had developed some infection in his knee and was operated upon, said an officer.
Factory worker Dhananjay Kumar and passer-by Manoj Kumar were also injured but they were discharged after first-aid. They were standing atop the adjacent building watching the firefighting operations and were caught in the flames that erupted after the tin shed collapsed, said a police officer.
Police suspected that the initial cause of the fire was an electric short-circuit. A case has been registered against unidentified persons and forensic teams will visit the spot to ascertain the exact cause.
Mourning Pal's death, Delhi BJP president Manoj Tiwari said society stands indebted to him for his services. He also requested Lt Governor of Delhi Anil Baijal to provide an alternative job for one of his family members.
A wreath laying ceremony was held at the Fire Safety Management Academy in Rohini and later his body was taken to Burari for the last rites.
Pal was due for a promotion in the next few days, said one of his colleagues.
His family is likely to get a compensation of Rs one crore as per a Delhi government's policy.
One of the injured firemen, Kumar, said, "Pal and I were on the second floor fighting the blaze when there was a blast and a tin shed collapsed. I was standing under a metal girder that didn't collapse. But since I was under the girder, I did not get trapped under the debris."
In 2016, six firemen died in separate incidents, most of them due to cylinder blast during firefighting, said a senior official.
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