Table 1.

Examples of heat and productivity suppression in different parts of the world

Geographic location and work activity; source of information, references	Heat and productivity effects
1. South African gold mine with >200,000 underground miners, who worked in extremely hot and humid conditions; 1956–1961 (11)	About 3.3 deaths/1,000 miners/year due to fatal heat stroke when wet bulb temperature (Twb) exceeded 34°C; 0.7 deaths/year/1,000 miners when Twb was between 31 and 33°C. Acclimatisation to heat before going underground reduced the risk, but even after acclimatisation two-thirds of new recruits were not able to carry out heavy labour in the hot work environment. Work intensity needs to be closely monitored by ‘boss-boys’ to detect early symptoms of heat stroke and force rest as required.
2. Agricultural workers in El Salvador and Nicaragua cutting sugar cane with a machete in the sun for 6–8 hours each day during a 3–5 month harvest; 2000–2008 (12, 13)	Young sugar cane workers have a very high rate of serious chronic kidney disease, which is often fatal. Daily dehydration due to heat and sweating, and without sufficient drinking water supply in the farm fields is a likely contributing cause, but other causes are being investigated. However, diabetes and hypertension cannot explain the high rates of this disease in this population. Sugar cane cutting cannot be carried out in the afternoons on sunny days due to excessive heat exposure, which reduces productivity.
3. South India assembly work in car and truck factories; 2008 (personal communication from company safety officers)	In these factories without air-conditioning, the air temperatures reach 42°C in the afternoons of the hottest months. The workers need frequent rest breaks to avoid heat stroke. At the car production line, this is achieved by employing two people to do one person's job. In the truck factory, much fewer orders are put through to the factory floor in the hottest months. Heat protection of workers reduces productivity.
4. Northern Vietnam shoe factory with 2,900 young women workers; 2002 (personal communication from factory manager)	The daily production target is the same throughout the year. In the cool period the workers start at 07.30 and in the hot period at 06.30. In the hot period they get longer rest breaks (three per day), and the actual daily working hours are greater than in the cool period in order to meet the production target. The reduced productivity caused by heat is compensated for by the workers’ longer working hours (at the same daily pay).
5. Southern states of the USA; early 20th century (14)	Economic historians have reported on the lower productivity in the southern parts of the USA before air-conditioning was introduced in factory and office buildings. The culture of the South, with its hot and humid climate conditions, was different from the North, and work was carried out at a more leisurely pace. One major reason for this difference was the physiological needs to ‘slow down’, which in other hot places of the world is demonstrated by ‘siesta’ and a working hour distribution very different from nine to five.