A part of the gas plant at St. Joseph’s College in which the explosion occurred; (right) the frame of the door that blew off. (Sanat Kr. Sinha)

A loud explosion in a small gas plant at St. Joseph’s College in Bowbazar blew off a plywood door on Monday morning, making students panic.

The plant produces gas that is used in Bunsen burners. When the explosion occurred at 9.20am, kindergarten students were in their classroom, about 20ft to the right of the plant, and senior students were in the chemistry laboratory, about 30ft to the left.

There was no one in the 10ftx6ft ground-floor room that serves as the plant at that time. Students immediately rushed out of the laboratory. Teachers escorted the kindergarten boys from the classroom to the field.

The authorities soon evacuated the three-storeyed building, which houses the ISC school’s junior section, and called the fire brigade.

By the time two fire engines arrived, the gas had dissipated. “There was no major damage. The reason of the explosion is unknown,” said a fireman.

Brother Christopher, an official of the school, said they could smell the gas after the explosion. “We do not know whether an electrical spark caused the explosion,” he said.

According to experts, an imbalance in pressure in the cylinder where the gas is stored could have caused the explosion. “If the outlet of the cylinder gets choked, the safety valve or the knob may burst because of the pressure and cause an explosion,” said D. Kundu, an associate professor of chemistry.

Like most other schools and colleges, St. Joseph’s gets its gas from Greater Calcutta Gas Supply Corporation. Because there was no piped gas supply on Monday, it had fired up the plant to supply gas to the chemistry laboratory, where students were working.

Each of the laboratories on the school’s ground floor has two fire extinguishers.

“None of the students was injured in the explosion and no complaint has been lodged,” said an officer of Bowbazar police station.