The three were struck by some poisonous gas in a tank of the plant at the apartment in Somasundarapalya, they said.
One of the men first entered the tank and raised an alarm. The other two rushed to his rescue, but they too met with the same fate.
On information, police rushed and retrieved the bodies of the three workers.
Bengaluru Development Minister K J George, city Mayor R Sampath Raj and civic body BBMP commissioner N Manjunath Prasad visited the spot.
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