Table 1.

Heat acclimation procedures used in Witwatersrand Gold Mines.

1886	Witwatersrand gold rush starts
1924	Deep City Mine reaches 0.6 miles and first recorded death from heat stroke occurs
1925	Underground acclimation being used in mines, but 4 deaths occur this year
1927	First recorded investigation into on-going heat-related deaths: acclimation modified:
	Natives without previous mining experience: 10 d light work in cooler areas
	Natives with previous experience: 5 d light work in cooler areas
1928	4 more heat-related deaths. Acclimation modified (“locally recruited assumes they were only recently discharged from service in some other mine”):
	New natives from native territories: 14 d
	New natives from local region: 7 d
	Natives discharged from hospital: 7–14 d
Jan 1930	An “alarming increase” in heat deaths even after 14 d acclimation.
	Add a 7-d red armlet period after acclimation
Late 1930	4 more heat-related deaths: modify acclimation:
	All new natives: 14 d acclimatization plus 16 d red armlet period
1930	Huge loss in working efficiency and still more deaths. Dreosti is employed to screen workers who need a longer acclimation by using a HTT (1 h shoveling rock in 95°F dry bulb, sat.)
Mar 1932	HTT used to identify 3 groups: Heat tolerant, Heat intolerant, Normal natives. Red armlet period is still 16 d.
	Acclimation protocols: HT (2–4 d)
	HIT (1–14 d)
	Norm (3–7 d)
Mar 1934:	Reduce red armlet period to 8 d.
1939:	Mechanical ventilation added to mines. HTT discontinued due to improved mine conditions. Minimal acclimation for all new natives.
1953:	Mining conditions worsen. Chamber of mines funds studies by Wyndham et al. to study ways to reduce acclimation protocols. New acclimation protocol is developed and found more effective while allowing more productive work to be done during acclimation.
	New acclimation protocol: 6 d normal mining load in a cooler slope (86.5°F, sat), then 6 d normal load in a hot slope (92°F).
1960s	Portable climatic tent used by Wyndham, Strydom, Mitchell et al to conduct a wide variety of scientific studies comparing Bantu, Bushmen, Caucasians, women, fitness, diet, and development of heat stress prediction equations.
1965	Climatic room acclimation procedures introduced:
	Miners block step for 4 h/d in a climatic room at 89°F, with workload increasing from 35 to 70 W over 12 d.
1976	Begin administration of Vitamin C which reduced the acclimation period from 12 to 8 d and reduced the % of heat intolerant miners from 5 to 1%.
1977	HTT reintroduced to assess acclimation. Block step at 54 W for 4 h at 92°F db/89°F wb
1982	Microcimate cooling is used to allow underground acclimation again at normal work rates and sites.
1991	A new HTT introduced for screening and a health monitoring program adopted:
	30 min block stepping at 80 W at a temperature of 85°F db/82 wb°F. Development of risk profile to determine fitness for work in a hot environment (age, obesity, medications, fitness, HTT results, med history). Heat stress monitoring procedures standardized (measure ambient conditions, fluid-replacement beverages, work-rest cycles, remedial actions for heat stress, communication facilities and action plans).