Eight people died and seven were injured when they accidentally triggered a fire extinguisher system inside the vault of a major Thai bank and released a suffocating cloud of chemicals, officials said yesterday.

The accident occurred on Sunday in a basement security vault at the Bangkok headquarters of Siam Commercial Bank (SCB), one of the country’s largest financial institutions.

SCB blamed the accident on contractors who had been working to upgrade the building’s chemical fire extinguisher system but mistakenly set it off, releasing a chemical retardant designed to starve any fire of oxygen.

“The work may have triggered the Pyrogen aerosol which, once triggered, will decrease oxygen – that could cause injuries and death,” the bank said in a statement.

Pyrogen manufactures a type of aerosol fire extinguisher for places where water cannot be used because it would damage documents or electrical equipment.

The company says on its website that its aerosol does not deplete oxygen.

But it advises against using it in occupied rooms and that “accidental exposure should be limited to five minutes”.