Final answer:
Equipment operators and maintainers may primarily be exposed to ETS via fossil fuel combustion, especially in tasks with close contact with combustion by-products or through point-source contamination from industrial plants.
Step-by-step explanation:
The primary source of environmental tobacco smoke (ETS) for equipment operators and maintainers, considering the context provided, seems to be the combustion of fossil fuels, especially through operations that involve high-sulfur coal, electric utilities, and various industrial processes. These occupational exposures can be exacerbated by tasks that involve close contact with combustion by-products, such as those found in greenhouses, tractor cabs, and the operation of fan mist sprayers. Furthermore, point-source contamination from wastewater treatment plants, factories, and combined sewers is a significant concern as it can directly affect workers who manage these operations, leading to dermal absorption of contaminants or inhalation in closed environments.
The primary source of excess toxic substances (ETS) for equipment operators and maintainers can vary depending on their job functions. Occupational exposure to ETS often occurs through absorption via exposed skin and inhalation. For example, equipment operators and maintainers who work in settings like spraying operations in greenhouses, enclosed environments, tractor cabs, and the operation of rotary fan mist sprayers may experience enhanced exposure to ETS through both skin absorption and inhalation.