The death of an elderly person and the injuries to four others, including two children, when a hydrogen gas cylinder exploded while inflating balloons in Nadia’s Santipur town late on Friday has raised questions about the monitoring mechanism of the district administration.

Sachin Biswas, 55, a vegetable seller, was killed in the explosion at a roadside stall during a Jagaddhatri idol immersion procession, Rajib Roy, 35, the gas balloon vendor, lost both his legs.

Initially it was thought that a cylinder containing helium gas had exploded as vendors use it to inflate balloons. But police and officials of the local administration said on Saturday that the vendor was using hydrogen gas, which is cheaper, without permission.

The accident has spread fear among locals as balloon vendors are expected to turn up at the Raas festival that begins in Santipur on Wednesday. A few lakh people gather in Santipur town for the annual event.

The Santipur municipality has banned the sale of balloons inflated with hydrogen. Municipality chairman Subrata Ghosh said: “We have issued a prohibitory order banning the sale of balloons inflated with hydrogen.”

The police have started a case of unnatural death and ruled out any slackness on their part.

“It becomes hard to track those selling gas balloons as they go to remote places. The vendor has lost his legs. We have not started any case against him,” an officer at Santipur police station said.

Fire services officials said monitoring was part of the police’s job even though the task of granting permission was theirs.

A senior official of the state fire service department said vendors selling balloons inflated with hydrogen needed to take permission from them. However, permission to use hydrogen gas is not being granted for the past several years in the wake of a number of accidents like the one in Santipur.

“It is the duty of the local police to check and ensure no vendor uses hydrogen to inflate balloons,” the fireman said.

Fire service officials said there was lack of awareness among police and common people about the dangers

of selling inflated gas balloons.

“According to the international fire safety code, inflation of balloons using hydrogen gas is prohibited. Our neighbouring country Bangladesh has also banned it. But we have no such prohibition here. As a result, vendors avoid using helium gas because of it is costly,” a fire official said.

A gas balloon vendor, who refused to be identified, said caustic soda (sodium hydroxide) and aluminium powder were used to produce hydrogen gas.

“While a cubic metre of hydrogen costs Rs 800, the same amount of helium costs Rs 2,700. If we have to buy helium, it will put us out of business,” he said.

Debajyoti Saha, an assistant professor of chemistry at Krishnagar Government College, said: “The reaction (of caustic soda and aluminium powder) is a continuous process and gas needs to be released intermittently to avoid pressure building up inside the cylinder.”

He said the Santipur vendor had either not released the gas at regular intervals or hydrogen may have come in contact with “a source of heat or fire”.