You are evaluating heat stress in workers digging a ditch by hand to lay sewage pipes. You obtain the following average values over a two hour period: Natural Wet Bulb (NWB) temperature = 27.0° C, Globe Temperature (GT) = 32.0° C, and Dry Bulb (DB) temperature = 30.0° C. Which WBGT index would you use to evaluate heat stress for this operation? Calculate a WBGT value for digging the trench. What control methods would you suggest to reduce the risk of heat illness in these workers?