Duties may risk exposure to adverse, environmental conditions such as dirt, dust, pollen, odors, animal pests, wetness, humidity, rain, fumes, temperature and noise extremes, loud machinery, vibrations, electric currents, traffic hazards, toxic agents, violence, disease and pathogenic substances. Duties involve regular and sustained performance of moderately to heavy, physically demanding work, typically involving but not limited to some combination of climbing and balancing, stooping, kneeling, crouching and crawling, lifting objects and human persons of various weights, pushing and pulling.