A chemical analysis method for detecting, identifying and reporting contraband, illegal drugs, explosives, toxic chemicals, decaying animal and vegetable matter, and concealed human beings located in secure spaces such as cargo shipping containers. Chemical analysis results are accumulated and added to effect definitive analyses over extended periods of time while the containers are in transit. Individual containers are equipped with a device employing the method. The analysis method consists of accumulation and addition of analytical chemical instrumentation, measurements of trace quantities of target chemical vapors inside of shipping containers while the containers are in transit. Cumulative and additive spectrometric analyses coupled with increased target chemical concentrations, due to chemical vapor build up over the long periods of time that containers are in transit, result in significantly increased electronic signal-to-noise in spectrometric measurements and increased spectrometric signal strengths that are indicative of the presence of target chemicals.