Method of sensing a gas concentration

A resealable gas concentration sensor for determining the concentration of a particular gas within a gaseous environment. The sensor is constructed of a housing and a cap. The cap is adapted to be temporarily coupled with the housing while in the environment to define a sealed sample chamber, thereby capturing a sample of the environment. A venturi tube having a narrow passage is affixed to the housing which is adapted to allow fluid flow through venturi tube into test equipment for determining the concentration of the gas in the sample. The housing and cap may be repeatedly uncoupled and resealed to capture additional samples and measure other concentrations.