Hong Kong enhances heat stress warning system after chorus of criticism, but rules still not binding

Hong Kong’s Labour Department has unveiled changes to its heat stress warning system following criticism that the existing thresholds meant no alerts were issued despite record-breaking temperatures this month.

The department said in a statement on Thursday that the Heat Stress at Work Warning (HSWW) system will feature two new trigger conditions from Friday to better protect workers in high-temperature environments. However, the rules are still not binding upon employers.

An outdoor worker in Hong Kong’s summer. Photo: Kyle Lam/HKFP.

Under these changes, the monitoring threshold for triggering higher-level warnings will be lowered when an “Extremely Hot Weather” Special Alert from the Hong Kong Observatory (HKO) is in effect.

When temperatures across Hong Kong reach 35 degrees Celsius or above, the system will lower the threshold and automatically raise the warning level by one step – from amber to red, or from red to black.

System under fire

Earlier this month, the HSWW system received criticism after the alert level remained at amber even as the city experienced its hottest day in 143 years on August 9.

Labour Department. File photo: Candice Chau/HKFP.

Former HKO director Lam Chiu-ying wrote on Facebook that it was “truly baffling” how record-breaking temperatures had only activated the lowest-tier Heat Stress at Work Warning.

He noted reports that the amber warning had been triggered more than 200 times since the system was introduced in May 2023, while red and black warnings had never been activated.

Two more former HKO chiefs later joined calls to revamp the system.

They pointed out that the Labour Department uses the HKO’s Heat Index (HI) as a reference for the HSWW – a “mismatch” since the HI is intended for the general public rather than outdoor workers.

Instead, they urged the department to adopt the wet-bulb globe temperature, an internationally recognised measure of environmental heat that accounts for not only air temperature but also humidity, heat radiation, and air movement.

Hong Kong saw a record-breaking heatwave in summer 2026. File photo: Kyle Lam/HKFP.

The department has not yet adopted this suggestion, but says it will consider it in the future.

“After the launch of the enhanced system, the Labour Department will continue to review the operation of the system and make improvements, such as studying whether to include other monitoring data, for example, the Wet Bulb Globe Temperature, as one of the indicators of the system,” the department’s statement on Thursday said.

Further changes urged

In response to the new amendments, a local charity supporting victims of workplace accidents said it believes the lowered thresholds will improve the HSWW system’s sensitivity, better addressing the heat stress experienced by workers.

Heatstroke levels. Photo: Labour Department.

The Association for the Rights of Industrial Accident Victims urged the Labour Department to review the enhanced system in a year, and to consider whether it should include the wet-bulb globe temperature as a reference point.

The NGO also urged the government to mandate that high-risk outdoor work must stop when a black heat stress warning is issued. For other warning levels, the group said, workers should be allowed to take rest breaks without facing penalties from their employers.