Commissioned by the Occupational Safety and Health Council, PolyU researchers have conducted a study to evaluate the effectiveness of cooling vests in protecting workers from heat stroke. It was concluded that a combo cooling vest is more accepted by workers in Hong Kong’s environment. In this issue of Excel@PolyU, Prof. Albert Chan, Acting Dean of the Faculty of Construction and Environment, shares the findings of this study.

What was the objective of the study?
We conducted on-site research and physiological examinations for workers of four industries – construction workers, horticulture workers and outdoor cleaners, airport apron workers and those work in kitchens/restaurants. Based on the results, the pros and cons of personal cooling equipment were assessed and its feasibility and suitability were determined.

How was the study conducted?
From July 2012 to June 2013, the research team visited the workplaces of these workers to gather on-site evidence in comparing the effectiveness of two styles of cooling vests - “passive system” vs “combo system”. Researchers also gathered vast amounts of indoor and outdoor data for each of the involved industries.

What are active, passive and combo cooling systems?
Active cooling systems are made up of external connection to air or liquid supplies, such as ventilated air cooling and circulated liquid cooling. They can also be installed with an internal device such as a battery-driven ambient air fan based garment. Active cooling can reduce both the cardiovascular and thermoregulatory strain.

Passive cooling systems utilize phase change materials (e.g. ice, frozen gel, salt or paraffin) in vests and clothing. As heat exchange media, phase change materials are characterized by their ability to absorb energy when they change from solid to liquid state and to release heat as they return to solid phase.

A combo system is one which combines active and passive cooling methods.

What were the research findings?
Participants who wore the “combo system” cooling vests had a 3.8 degree of difficulty of work on average (the highest index is 10), which was lower than the 4.58 degree on average for those who wore the “passive system” cooling vests. The majority of the participants (83 out of 111 participants) from the four industries preferred the “combo system” cooling vests.

How does the “combo system” cooling vest work?
The vest is installed with small fans on both sides at the back, with built-in cooling packs that can be changed and used repeatedly. The evaporation of sweat can be facilitated for wearers, keeping their bodies cool and dissipating the oppressive heat. Therefore it can reduce the risk of heat stroke and is suitable for outdoor workers and those who work in blazing hot conditions.

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