INS Sindhurakshak is one of the classic diesel-electric submarines. When it goes beneath the water, the submarine runs on the electric energy stored in the submarine batteries.
The submarine batteries are capable to store large quantity of energy.
There are usually two battery rooms on a submarine. Forward battery room is placed beneath the officer’s quarters and aft battery room is beneath control room.
The cells in a battery are connected each other in serial connection and the batteries are connected each other in serial or parallel connection.
When the battery is charging and discharging harmful gases including hydrogen are created. 1 ampere per hour develops approximately 1 cubic centimeter of hydrogen.
The built-up of hydrogen is sucked out using two blowers.
If the blowers do not perform properly, the level of hydrogen can exceed.
Hydrogen gets inflammable if its higher than 4.5 percent in the air, a mixture with an hydrogen content above 9 % makes it explosive.
The possibly of volatile hydrogen gas during battery charging onboard INS Sindhurakshak cannot be ruled out
Two separate explosions happened almost simultaneously, one after the other on the aft side of the shift, which is adjacent to the ship’s torpedo department.
The first explosion was comparatively small, and could have triggered the second explosion.
There would have been no reaction time for the sailors to prevent damage.