Police have charged the owner of Na Ladprao beer hall with six offences following a fire last month that killed 37 people and injured 77 others.

Pol Maj Gen Kiatikul Sonthinen, commander of Metropolitan Police Division 2, said investigators had completed a seven-volume case file after questioning 211 witnesses, including employees, customers, relatives of victims, experts and forensic officers.

The investigation identified Suwicha Salaibat, 45, the venue owner, as being responsible for the incident. The case has been forwarded to prosecutors for consideration.

Mr Suwicha was charged both as an individual and on behalf of the company with reckless arson causing death, negligence causing death, negligence causing serious injury, negligence causing physical and psychological harm, and property damage. He was also charged with operating an entertainment venue without a licence.

Police said the fire was caused by an electrical short circuit following modifications to the venue's electrical system. Sparks ignited soundproofing materials, causing the blaze to spread rapidly.

Pol Maj Gen Kiatikul said the venue's layout also hampered evacuation efforts. Numerous tables obstructed movement, while doors designated as emergency exits were blocked, locked or otherwise failed to comply with legal requirements.

Witness testimony from employees and customers supported the conclusion that the owner had failed to take reasonable safety precautions expected of an entertainment venue operator, he said.

Mr Suwicha has yet to be questioned because he remains in intensive care at Paolo Kaset Hospital. Investigators questioned his four business partners but found no evidence linking them to the management of the venue. The July 12 fire claimed 37 lives, including victims who later died in hospital, and left 77 people with burn injuries.

Separately, city authorities have stepped up safety inspections of entertainment venues in the wake of the tragedy. Between July 19 and Aug 4, Bangkok Metropolitan Administration teams inspected 948 establishments. Of those inspected, 209 met safety standards, 632 were ordered to make improvements and 107 were ordered to cease operations.

The inspections cover 17 safety criteria, including fire prevention, hygiene and building safety. Bangkok deputy governor Pornphrom Vikitsreth said operators would be given an opportunity to rectify non-critical deficiencies, while serious safety violations would face legal action.