Final answer:
Burning of plastics in open burn barrels is the human activity most likely to cause an increase in cases of heat exhaustion among humans.
Step-by-step explanation:
The human activity that is most likely to cause an increase in the number of cases of heat exhaustion among humans is burning of plastics in open burn barrels. When plastics are burned, they release toxic fumes and chemicals into the air, including carbon monoxide and volatile organic compounds (VOCs). These pollutants contribute to air pollution and increase heat in the environment, which can lead to heat exhaustion and other heat-related illnesses.
Learn more about heat exhaustion