The thermal work limit adds together four measures – air temperature, humidity, wind speed and exposure to radiant heat from the sun – to gauge how dangerous a working environment is. The lower the TWL, the harsher the environment.
The measure is a heat-stress index - in other words, what controls are needed when working under specific heat conditions. It has been drawn up by the Health Authority-Abu Dhabi, which is pushing for it to be given legal teeth.
A TWL above 220 is in the unrestricted zone. There is no limit on work for workers who are drinking adequate fluids and can take rest breaks when they need to.
Between 140-220 is the "acclimitisation zone". There is still no restriction placed on acclimitised workers who are used to working in heat and not new to the UAE or who have been on holiday in a colder climate. But workers should be aware of an increased risk of heat illness and should not work alone if not acclimatised when returning from leave.
Between 115 and 140 is the buffer zone – where environmental conditions could limit work. Shade ought to be provided as well as better ventilation. Working alone outside should be avoided, unacclimatised workers should not be at work and frequent rests
scheduled. An adequate intake of fluid is also required to ensure proper replacement of fluids lost in sweat in the specific hot environmental conditions.
A TWL below 115 is in the withdrawal zone. At this level, work is regarded as unsafe, meaning only maintenance and rescue operations should take place. No person should work alone, work must be specifically authorised, and for every 20 minutes of work, 40 minutes of rest must be scheduled. Workers must drink 600ml of water every half-hour and compulsory dehydration testing is required at the end of each shift.
According to experts at Haad, the withdrawal zone is rarely experienced in the UAE.
Further information is available from Haad’s Safety in Heat website: www.haad-safe.ae