Gases in the cabin can be tested using gas chromatography, mass spectrometry and infra-red spectrophotometry. Samples of air from the spacecraft are examined both before and after flight for their gas concentrations. The activated carbon filters can be examined for evidence of trace gases. The concentrations measured can be compared with the appropriate exposure limits. If the exposures are high then the risks to health increase. The ongoing sampling of the hazardous substances is essential so that appropriate action can be taken if exposure is high.