A chemical accident in the basement of the Bangkok’s Siam Commercial Bank has killed eight people, Thai officials have confirmed.

The contractors were working on a fire safety system at the headquarters of the bank on March 13, the bank said in a statement.

The workers apparently suffocated after a gas mixture which depletes oxygen was released.

Another seven were injured in the incident, which may have been caused by contractors’ “negligence”, the bank’s statement added.

The incident took place in a vault storing documents in the head office in Bangkok.

The Siam Commercial Bank said at around 21:30 local time on March 13, an aerosol system called pyrogen was “inadvertently activated and exhausted all the oxygen in the area” as contractors were working on it.

Pyrogen involves a mixture of gases including potassium carbonates, nitrogen, carbon dioxide, carbon monoxide, nitrogen oxide and ammonia.

The system works by removing all oxygen from the air to stifle a fire.

According to the Bangkok Post, that firemen encountered delays as they tried to reach the victims due to tightly locked doors.

The Siam Commercial Bank, one of Thailand’s largest financial institutions, added that it would provide assistance to those in the accident and operations would continue normally.

Correspondents say that fatal industrial accidents remain rare in Thailand.