Describes experiments emitting a gaseous tracer (methane) into a ventilated test room and measuring gas concentration with rapid-response hydrocarbon analyser. Parameters were contaminant source location, sample location and ventilation rate. Measures equilibrium concentrations and rates of decrease in concentration following cessation of tracer release. Subjects data to multifactorial analyses. States goals of research were to characterise dispersion and dilution of air contaminant within enclosed, ventilated space, to detect and analyse deviations from perfect mixing and to develop a study method applicable to work space and laboratories.