The Labour Department has changed the Heat Stress at Work Warning (“HSWW”) system following concerns that its thresholds did not adequately reflect severe conditions.
On 9 August 2026, the Hong Kong Observatory recorded 36.9°C, the highest temperature since records began in 1884, but the HSWW did not rise above Amber, the lowest of the three warning levels. The incident renewed debate over whether the Hong Kong Heat Index, which is intended as a general heat-stress indicator, is sufficiently tailored to workplace exposure.
The HSWW is based on (i) the Hong Kong Heat Index (“HKHI”), which includes data such as environmental temperature, humidity, air flow, and solar radiation levels; (ii) measured temperatures across Hong Kong; and (iii) the Hong Kong Observatory’s “Extremely Hot” Special Alert.
The HSWW adopts the following three warning levels:
- Amber (HKHI of 30 to below 32): indicates high heat stress in certain work environments;
- Red (HKHI of 32 to below 34): indicates very high heat stress in certain work environments; and
- Black (HKHI of 34 or above): indicates extremely high heat stress in certain work environments.
With effect from 28 August 2026, the HSWW has been enhanced to introduce two new triggering conditions aimed at better safeguarding the occupational health of employees working in hot weather or high-temperature environments. The two new triggering conditions:
- First, when the Hong Kong Observatory’s "Extremely Hot Weather" Special Alert is in effect, the Labour Department will issue the Amber Warning immediately and the threshold for triggering a higher level of warning will be lowered even if the HKHI has not reached 30. This enables the earlier activation of a higher warning level; and
- Second, when temperatures across Hong Kong generally reach 35°C or above, in addition to lowering the threshold for triggering a warning, the warning level will be raised by one level automatically. If the Amber or Red Warning is in effect it will be elevated to the Red or Black Warning respectively. This is to alert the public to the health risks of heat stress when working under abnormally high temperatures.
Employers should continue to pay attention to the HSWW level issued by the Labour Department and make corresponding work arrangements to reduce the employees’ risk of heatstroke. The HSWW and the associated work/rest recommendations are guidance rather than statutory requirements. Even so, employers remain responsible for assessing heat-related risks and taking suitable measures, which may include providing shaded rest areas, providing ventilation and cooling equipment, rescheduling strenuous tasks and reminding employees to stay hydrated and rest periodically.
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