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Despite record-breaking temperatures in Hong Kong, the Labour Department’s Heat Stress at Work Warning system remained at the lowest level of amber on August 9.

The reason for this absurdity is the use of the Hong Kong Heat Index (HKHI) in determining the threshold for issuing the three levels of warning – amber at 30, red at 32 and black at 34.

HKHI was developed through research by the Hong Kong Observatory and Chinese University as an indicator of the risk of emergency hospital admission for the public in Hong Kong. The Wet Bulb Globe Temperature (WBGT), on the other hand, is widely used around the world to assess heat exposure at work, including by international standard ISO 7243.