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

Hong Kong’s Labour Department has introduced adjustments to its heat stress warning system following widespread criticism that existing thresholds failed to adequately protect workers during record-high temperatures this month.

In a statement issued Thursday, the department announced that the Heat Stress at Work Warning (HSWW) system will implement two new trigger conditions starting Friday. These changes aim to enhance protections for workers in high-temperature environments. However, the updated rules remain non-binding for employers.

Under the revised system, if the Hong Kong Observatory (HKO) issues an "Extremely Hot Weather" Special Alert, the threshold for triggering higher-level warnings will be reduced. Additionally, when the city’s temperature reaches or exceeds 35 degrees Celsius, the system will automatically elevate the warning level by one step—from amber to red or from red to black.

The adjustments come after the HSWW system faced criticism earlier this month for failing to escalate warnings despite Hong Kong recording its hottest day in 143 years on August 9. Former HKO director Lam Chiu-ying publicly questioned why record-breaking temperatures had only triggered the lowest-tier amber warning. He noted that since its introduction in May 2023, the amber warning had been activated over 200 times, while red and black warnings had never been issued.

Two other former HKO directors subsequently joined calls to reform the system, arguing that the Labour Department’s reliance on the HKO’s Heat Index (HI) was mismatched for outdoor workers. The HI is designed for the general public rather than those working outdoors, they pointed out. They advocated for adopting the wet-bulb globe temperature (WBGT), an internationally recognized measure that considers humidity, heat radiation, and air movement in addition to temperature.

While the Labour Department has not yet incorporated WBGT into the system, it stated in its announcement that it would consider doing so in future reviews. "After the launch of the enhanced system, the Labour Department will continue to review its operation and make improvements, such as studying whether to include other monitoring data, for example, the Wet Bulb Globe Temperature, as one of the indicators," the statement read.

A local charity assisting victims of workplace accidents welcomed the lowered thresholds, stating they would improve the system’s sensitivity to heat stress risks. The Association for the Rights of Industrial Accident Victims urged the Labour Department to evaluate the updated system within a year and consider adopting WBGT as a reference. The group also called on the government to mandate that high-risk outdoor work cease during a black heat stress warning and to ensure workers can take rest breaks without facing penalties from employers at all warning levels.