General Description The 720b is an advanced state-of-the-art leak detector capable of detecting many combustible, noncombustible and toxic gases. 4. The following is a partial list of gases that the 720b is sensitive to: Acetone, Alcohol, Ammonia, Steam, Carbon Monoxide*, Butane, Gasoline, Jet Fuel, Hydrogen Sulfide, Smoke, Industrial Solvents, Methane, Lacquer Thinner, Naphtha, Propane, Natural Gas. *Not to be used to quantify the amount of CO present. Operating Instructions: 1.