A source said a 40-year-old project manager of the main contractor who had earlier helped with the investigation was also arrested and charged with manslaughter. However, the insider said the manager’s case would not be heard in court on Friday.

The two workers, aged 61 and 63, died on Sunday after being trapped in the underground tube for more than 12 hours at a construction site managed by the MTR Corporation at 1 Austin Road West in the West Kowloon Cultural District.

The case sparked calls from a concern group for authorities to require all contractors to report operations in confined spaces and step up site checks.

Fay Siu Sin-man, chief executive of the Association for the Rights of Industrial Accident Victims, said such mandatory measures could provide the government with an overview of construction works in enclosed environments citywide.

“It can serve as a precaution for contractors as they have to notify authorities and will expect inspections. It can effectively promote safety,” Siu told a radio programme on Thursday.

She was hoping to extend the scope of the Construction Sites (Safety) Regulations, which currently only requires contractors to notify the Labour Department on works lasting for at least six weeks and engaging more than 10 workers.

There had only been two convictions linked to works in confined spaces in the past three years, Siu noted, attributing the low number to the lack of knowledge by the government about such sites.

She also voiced hope authorities could increase manpower to step up site inspections, adding it should not be too difficult for contractors to notify the government.

But Hong Kong Construction Sub-contractors Association president Lawrence Ng San-wa said that notifying the government of confined works was easier said than done.

“We have over 1,000 sites operating every day. Each site can involve a few confined spaces … It will take a lot of procedures,” Ng argued on the same radio show.

He added that the question of who should bear the responsibility for the tragedy hinged on the agreement signed between the main contractor and subcontractors, noting the former sometimes passed key safety duties to the latter.

“According to labour laws, the employer must be responsible for ensuring workers’ safety … But in contract management, the main contractor also has relevant responsibilities,” he said.

Hong Kong Institute of Construction Managers honorary treasurer Chan Chi-man suggested setting up a registration system for the site foreman, who is responsible for supervising and coordinating workers. He said the move would be a more direct way to improve site safety.

“The incident reflects that the regulation does not have a major flaw but it is mainly about whether persons have acted responsibly and if the measures have been executed,” Chan said.

Separately, Secretary for Labour and Welfare Chris Sun Yuk-han said the government would look into the responsibilities of different parties involved in the case.

“The MTR is the occupier of the site … It has hired other companies for the construction,” Sun said.

“We will definitely focus on the contractor and we will look into whether the site occupier is involved. But past experience has shown that the problem normally lies with the contractors.”