Workers in this unit group operate and service stationary engines and related equipment. Their functions include: operating and servicing various types of stationary engines and related mechanical equipment; operating and servicing a particular type of stationary engine or installation such as compressor, steam boiler, pumping equipment, water treatment plant, incinerator, refrigeration unit, ventilation and heating installation; performing related tasks. Crane and hoist operators, including Opening bridge operator, are classified in unit group 9-73.