In water treatment plants equipped with large–scale ozonation facilities, specific safety measures must be constantly reviewed and tested. Safety of employees : in high concentrations, ozone becomes a poisonous gas. This requires adequate means for detection of ozone in traces in the ambient air. ventilation and destruction. individual protection Safety of plant and equipment : ozonation has become an essential phase in the treatment process and ozonators must be fitted with safety devices for the detection and rapid control of hazardous conditions.