Essential functions are regularly performed without exposure to adverse environmental conditions; performance of functions in the field may require exposure to adverse environmental conditions, such as dirt, dust, pollen, odors, wetness, humidity, rain, fumes, smoke, temperature and noise extremes, hazardous materials, fire, unsafe structures, heights, confined spaces, machinery, vibrations, electric currents, traffic hazards, bright/dim lights, toxic agents, human bites, explosives, water hazards, violence, disease, pathogenic substances, or rude/irate people. Tasks require the regular and, at times, sustained performance of moderately physically demanding work, typically involving some combination of climbing and balancing, stooping, kneeling, crouching, and crawling, and that may involve the lifting, carrying, pushing, and/or pulling of heavy objects and materials.