Ozone generation uses a significant amount of electrical power. Thus, constant attention must be given to the system to ensure that power is optimized for controlled disinfection performance. There must be no leaking connections in or surrounding the ozone generator. Therefore, leaks should be checked for routinely, since a very small leak can cause unacceptable ambient ozone concentrations. The ozone monitoring equipment must be tested and calibrated as recommended by the equipment manufacturer. The operator must on a regular basis monitor the appropriate subunits to ensure that they are not overheated. Like oxygen, ozone has limited solubility and decomposes more rapidly in water than in air. This factor, along with ozone’s reactivity, requires that the ozone contactor be well covered and that the ozone diffuses into the wastewater as effectively as possible. Ozone in gaseous form is explosive once it reaches a concentration of 240 g/m3 . Since most ozonation systems never exceed a gaseous ozone concentration of 50 to 200 g/m3 , this is generally not a problem. However, ozone in gaseous form will remain hazardous for a significant amount of time; thus, extreme caution is needed when operating the ozone gas systems. It is important that the ozone generator, distribution, contacting, off-gas, and ozone destructor inlet piping be purged before opening the various systems or subsystems. When entering the ozone contactor, personnel must recognize the potential for oxygen deficiencies or trapped ozone gas in spite of best efforts to purge the system. The operator should be aware of all emergency operating procedures required if a problem occurs. All safety equipment should be available for operators to use in case of an emergency.