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The hot and humid summer in Hong Kong poses an increased risk of heat stroke to employees
working outdoor or in indoor environments that lack air conditioning systems. Therefore, employers are required to conduct risk assessments on the heat stress of employees at work, by considering the various heat stress risk factors (including working environment, workload and personal factors, and take appropriate measures for prevention of heat stroke and help employees to cool down the body, and arrange appropriate rest breaks in times of Heat Stress at Work Warnings. The employees take measures to prevent heat stroke arranged by their employers at work, to safeguard their own occupational safety and health and reduce the risk of heat stroke.

It can be calculated by using the “Rest Time Calculator” on the webpage.

For details, please refer to the Guidance Notes on Prevention of Heat Stroke at Work issued by the Labour Department, in particular, the Workplace Heat Stress Risk Assessment Form in Appendix 2, Physical Workload Categories and Examples in Appendix 1 and Rest Arrangements for Outdoor Work in Times of Heat Stress at Work Warning in Appendix 4 of the Guidance Notes.

In general, the physical demand can be determined by the physical activities and the carrying load at work. The following are the four levels of physical workload categories and examples.

Note: The above examples of industries are based on general working conditions of individual occupations and are for reference only. Employers should make reasonable judgments based on the actual job nature of their employees in the risk assessment.

Employers/ Employees should calculate the rest time based on the workload performed during the hour after the Heat Stress at Work Warning is in effect. If two levels of workload are performed in the same hour, the rest time should be calculated according to the dominant workload performed during that hour. When the working time of different levels of workloads are similar, the heavier level of workload should be adopted for the calculation.

Employers may appoint a person who is familiar with the working conditions of the workplace and has basic occupational safety and health knowledge about heat stress to conduct the risk assessment. In addition to considering the various heat stress risk factors (including environmental, work and personal factors), appropriate preventive and control measures should also be recommended based on the different risk factors identified.

If employers cannot take appropriate heat stroke prevention measures according to the Guidance Notes on Prevention of Heat Stroke at Work, due to the unique working conditions and needs of their employees, they could contact the Occupational Safety and Health Branch of the Labour Department at 2559 2297 (auto-recording service available outside service hours) for enquiry, or seek the opinion and assistance of occupational health professionals.

When Hong Kong Heat Index reaches the respective levels of Heat Stress at Work Warning coded Amber, Red and Black, the Hong Kong Observatory will assist the Labour Department in displaying relevant information on Heat Stress at Work Warning on the homepage of its official website and the “My Observatory” mobile application. The public can also receive details of the Heat Stress at Work Warning by
allowing push notifications from “My Observatory” mobile application. In addition, the Labour Department will issue prompt message to the public regarding the coming into effect of Heat Stress at Work Warning through press releases and the “GovHK Notifications” mobile application. In addition, various electronic media will also disseminate relevant information through appropriate channels.

The main purpose of HSWW is to warn about the significant heat stress and health risks posed by the weather in Hong Kong as a whole to employees working outdoors or in indoor environments without air-conditioning systems overall, and to remind employers and employees to take necessary preventive measures to reduce the risk of heat stroke at work.

The establishment of HSWW does not obviate the responsibility of employers to assess safety and health risks in the workplace. If employers and employees believe that, due to the special circumstances of the workplace (e.g. geographical location, working environment), the HSWW does not fully reflect the real-time risk of heat stress posed to employees at work by the weather conditions or environment in the workplace, the employers have the responsibility to make assessment accordingly, such as seeking occupational health professionals to measure the WBGT index at the workplace for evaluating the level of heat stress faced by the employees, and taking corresponding preventive measures based on the results to reduce the risk of heat stroke at work.

After the issuance of a Heat Stress at Work Warning, employers are required to arrange rest breaks according to the workload of employees. Besides “Suspension of work” arrangement, which should be implemented immediately, employers can flexibly arrange for employees to have the recommended rest time during the hour.

The work / rest arrangements recommended in The Guidance Notes on Prevention of Heat Stroke at Work published by the Labour Department are not applicable to work that needs to be performed urgent or emergency work, such as firefighting, emergency rescue, or urgent repair work. Therefore, relevant employers/ responsible persons should develop necessary control measures in advance for employees engaged in such work to prevent heat stroke while performing relevant duties. For enquiry, please contact the Occupational Safety and Health Branch of the Labour Department at 2559 2297 (auto-recording service available outside service hours), or seek the opinion and assistance of occupational health professionals.

Apart from weather conditions, physical work generates heat and increases heat stress. Employers should reduce heat stress during work, as far as reasonably practicable, let employees to have rest break. For instance, employees should let employees performing light to moderate levels of physical work have a minimum of a 10-minute rest break after every 2 hours of work, while employees performing heavy to very heavy levels of physical work should be given at least a 15-minute rest break after every 2 hours of work,
to allow employees to recuperate, drink water and cool down their body.

“Heat Acclimatization”means the gradual physiological adaption of the body to enhance the ability to withstand heat stress. If an employee has not worked in a hot environment for more than a month or has never worked in such environment, the employer should arrange a minimum acclimatization period of five days to allow the employee to fully adapt to working in a hot environment. On the first day, the employee’s work in a hot environment should not last for more than 20% of the normal working time in such environment. The working time can then be increased by 20% of the normal working time in hot environment each day until the employee fully adapts and can work normally in the hot environment.

If an employee has not worked in a hot environment for two weeks to one month, the employer should also arrange a minimum acclimatization period of four days when the employee returns to work to allow them to re-adapt to working in a hot environment. On the first day, the employee’s work in a hot environment should not last for more than 50% of the normal working time in such environment. The working time of the employee can then be increased stepwise by 20% of the normal working time in hot environment each day until it returns to the normal working time in hot environment.

Apart from heat acclimatization, if employees have underlying health conditions such as heart disease, hypertension, or are taking certain medications, they may have an increased risk of heat stroke while working in hot environments. If they have doubts about whether their health condition is suitable for working safely in high temperatures, they should consult their doctors, inform their employers of any relevant advice and discuss with them about the appropriate work arrangements.

from exposure to direct sunlight. Employers/ responsible persons should provide shade or sun-blocking cover, it would be effective to minimize direct sun exposure when covering most parts of the body. Using misting fans indoors can increase humidity in the environment, which can affect the heat dissipation effect. Therefore, misting fans are generally more suitable for use in outdoor environments.

In view of the varying nature and demands of different industries and job positions, employers should implement different control measures for reducing heat stress. For further enquiry, please contact the Occupational Safety and Health Branch of the Labour Department at 2559 2297 (auto-recording service available outside service hours), or seek the opinion and assistance of occupational health professionals.

Also, employers could establish reasonable and mutually agreed heat prevention measures and improve the effectiveness of preventive measures through consultation with employees such as safety committee of the organization.

Generally speaking, in indoor work environments equipped with air conditioning systems, the air temperature and relative humidity can be controlled at 23°C to 26°C and 40 % to 70 % respectively. An air cooler could not achieve such effect.

Adequate air movements through inlets and outlets in an indoor area are essential for natural ventilation. For buildings that rely entirely on natural ventilation, the ventilation openings should be at least 5% to 10% of the floor area to obtain adequate ventilation in summer.

Some examples on ineffective control measures on reducing heat stress from heat sources or heat-generating facilities nearby the working locations:

• No effective devices installed in the kitchen to remove the hot air and humidity generated by cooking process;
• No exhaust device used to remove the hot air generated during gas welding or flame cutting processes;
• No heat shield installed for heat-generating facilities near the working location, which results in higher temperatures in the work location.

Common non-breathable protective clothing includes: coveralls which are impervious to dust or chemicals donned for asbestos removal work or pesticide spraying work; and protective isolation gowns donned by healthcare workers. However, reflective vests and aprons only cover parts of the body, only posed limited impact on heat dissipation, and are not considered as non-breathable clothing.

In addition to the time of rest, the place of rest is also very important. Employers/responsible persons must arrange covered or shaded places for employees working outdoors so that employees can sit and rest. Rest areas should be well ventilated, ideally with air conditioning. If it is not possible to arrange a shaded resting place, it is necessary to give employees a longer rest time to relieve heat stress. In remote workplaces with no electricity supply, employers/persons in charge may consider setting up mobile solar cooling rest stations for the use of relevant employees.

Apart from rest breaks, the location of the rest area is equally important in managing heat stress. Employers / responsible persons should set up or arrange shaded areas for employees performing outdoor work to sit down and rest. Rest areas should have good ventilation or, better still, air conditioning, if available. If shaded rest areas are not available, employees may require longer breaks to alleviate heat stress. In remote and off-grid working locations, employers or responsible persons may consider installing mobile cooling stations for relevant employees to use.

The Occupational Safety and Health Council has developed the “Solar Cooling Kiosk” that provides a shady area with good ventilation for employees working in rural and remote areas to rest and drink water: https://bit.ly/3BhETBp