The Hach Orbisphere 366xEx Controllers family of instruments measures oxygen (O2), hydrogen (H2), and ozone (O3) in areas where hazardous and flammable conditions are possible. When coupled with a choice of membrane covered, electrochemical sensors, the 366xEx is suitable for sampling dissolved concentrations from trace ppb to supersaturation, and gaseous concentrations from ppb to percent (%) levels. These sensors can be constructed from a variety of chemically resistant materials and use an assortment of membranes with permeability and chemical resistance to optimise long-term measurement performance.