Human Engineering (HE) is the discipline that addresses the safety, effectiveness, role, and integration of people in the operation, use, and maintenance of a product. A part of the total system design process, HE examines how the design of the product affects human welfare and how people interact with the product. These people include users, operators, and maintainers of the product. The physical structure and mechanical operation of the human body and functioning of human senses determine how people can interact with a product. This interaction is usually referred to as the man-machine interface. In some textbooks, maintainability is included as a subset of HE. The ease and economy with which maintenance can be performed is partly a function of how well the designers have considered human limitations and abilities in regard to strength, perception, reach, dexterity, and biology. Certainly, the HE and maintainability engineers have related and often common goals. Close coordination and communication between the two disciplines is, therefore, essential.
Maintainability is directly related to the anthropometric and psychological characteristics of the human beings who will operate and maintain the product. The maintainability engineer must collaborate with the human factors engineer, and consider human engineering factors during design efforts, to ensure the required range of expected human maintainers can indeed accomplish the tasks. Anthropometric characteristics determine how large access openings must be, the need for stands, how far replaceable units may be placed inside a compartment and still be reachable, and so forth. Psychological factors determine what types of warnings are most effective, which way a calibration knob should turn, whether a continuously variable or detented knob should be used, and so forth.