Fire Hazards of Refrigerants in Air Conditioning Control System

Air conditioning control systems are commonly installed in restaurants, commercial buildings, office buildings and institutional buildings in Hong Kong. The systems invariably involve the use of fans for moving the air, filters for cleansing, ducts for air distribution, a control system for regulating the amount of heating or cooling automatically and a refrigerating plant connected to the heat exchange surface. The ducts in turn present the possibility of spreading fire and smoke throughout the building or areas served. According to the local Code of Practice for Minimum Fire Service Installations and Equipment, when a ventilation or air conditioning control system to a building is provided, it shall stop mechanically induced air movement within a designated fire compartment. In order to fulfil such requirement, the architects and building services engineers will design to install associated equipment of air conditioning control systems to satisfy the relevant fire safety requirements of the local authority, which includes the provision of fire resisting ducting, fire dampers, smoke detectors and fire resisting cables, etc. However, lessons learned from past experience reveal that owners or property management staff of the buildings or covered areas and maintenance contractors will mainly concern the efficiency and energy saving of the systems without paying much attention to the fire hazards arising from the use of refrigerants. It is also noted that fire or explosion incidents involving air conditioning control systems are often attributed to improper maintenance work conducted by maintenance contractors, such as refilling the refrigerating plant with poor quality refrigerants, recharging refrigerants incompatible with the metal parts of the system, refilling refrigerants at high pressure resulting in bursting of piping and joints, valves contaminated by grease, presence of an ignition source in close proximity of the refrigerating plant, etc. In general, refrigerants present two basic hazards, namely toxicity and flammability. Refrigerants mix readily with air and if flammable, may reach flammable concentrations ready to be ignited by an ignition source. As diffusion may not take place rapidly enough to avoid the hazards in the event of leakage, fire or explosion may occur. With reference to a fire with explosion incident involving air conditioning control system in a restaurant in Hong Kong, this paper will outline and discuss the fire hazards of refrigerants in air conditioning control systems.