Regular checking on the cleanliness of the ventilation systems, as well as their periodic cleaning and, if necessary, disinfection are for the proper maintenance of each system. During maintenance operations (repairs, cleaning, filter replacement), workers are at risks associated with exposure to hazardous chemicals and harmful biological agents. In ventilation systems there are usually favorable conditions for the development of microorganisms, mainly bacteria and fungi, due to surfaces contaminated with dust particles or increased humidity caused by ventilation ducts, air filters, thermal insulation, noise dampers, air coolers, etc. Workers who perform cleaning and disinfection operations on ventilation systems are exposed to chemical agents through contacts with contaminants released from sealing materials, adhesives, fireproof lining and insulating materials, volatile organic compounds present in air filters, noise dampers and insulating materials, as well as with cleaning agents and disinfectants. Exposure to harmful chemical and biological agents may induce adverse health effects ranging from allergic reactions and irritation through infections to toxic reactions and other non-specific symptoms. Due to lack of studies on the exposure of this group of workers, employers face great difficulties in identifying hazards, which prevent them from performing an occupational risk assessment.