A similar explosion on the INS Sindhurakshak three years ago had killed one crew member and injured two submariners in in Visakhapatnam in February 2010. A navy probe had then concluded that the accident occurred due o a faulty battery valve that leaked hydrogen. The conventional submarine is powered by a mix of diesel generators and electric batteries.
Vice Admiral AK Singh (retd), who headed the navy’s submarine arm in the late 1990s, said, “A spark can cause an explosion if there’ is hydrogen build up during battery charging. A 4% hydrogen concentration can prove to be disastrous.” He said the fire could have engulfed the weapons compartment and caused the explosion.
The Kilo-class submarines have more than 500 batteries.