Fay Siu Sin-man, chief executive of the Association for the Rights of Industrial Accident Victims, said that sometimes workers were asked to go beyond their specified duties, which only required them to use a high-pressure hosepipe to clean drains from outside.

“According to the sector, the drains are often clogged by trash. They need to empty the waste water and send workers underground to clear the trash,” Siu told a radio show on Wednesday.

“We should have foreseen that this could happen and had a comprehensive plan to handle work in confined spaces.”

She urged the government to provide more details about the incident and review whether there were problems with the contractors’ safety measures.

The two men were rescued by firefighters from the manhole at Yuen Wo Playground in Sha Tin on Monday. The pair were taken to hospital unconscious but certified dead soon after arrival.

Two other colleagues also entered the manhole and reported feeling unwell.

The father of one of the victims questioned why the workers had gone underground, which was the key focus of the government’s investigation.

Death of 2 Hong Kong sewer workers sparks calls for action to plug safety gaps

Lee Kwong-sing, a safety adviser with the Hong Kong Construction Industry Employees General Union, also said workers occasionally needed to venture underground even though they were not strictly required to do so.

He said the law stipulated that contractors conducting site assessments must implement safety measures and provide protective gear for staff working underground, but there was no sight of such equipment at the scene.

“I wonder if there is a problem with the management systems and whether supervisors were aware of the situation,” Lee said on the same radio programme.

“It seems like there were no supervisors at the site. This can be a serious loophole.”

He added that the law should also apply in the latest case, as the works were taking place near a confined space, and the contractors should have taken safety precautions.

Labour minister Chris Sun says a revised safety code for working in confined space will be ready in one to two months. Photo: Yik Yeung-man

Lawmaker Chau Siu-chung from the Federation of Hong Kong and Kowloon Labour Unions also told the radio show that the government needed to look into whether contractors had followed safety guidelines, such as implementing measures to prevent workers from slipping and falling.

Secretary for Labour and Welfare Chris Sun Yuk-han said on Tuesday a revised safety code for working in confined spaces would be ready for release in one to two months and included the use of more technology to improve safety in manholes.

Chau said that, according to his understanding, the new code might require contractors to equip underground workers with sensors and set up lifting machines to rescue them if needed.

He added that the government was also looking into amending the current regulation, which only required contractors to notify authorities of works lasting longer than six weeks or hiring more than 10 workers.

The changes might require contractors to report any works involving potentially dangerous procedures before commencing, regardless of the duration and manpower needed, he said.