Hydrocarbon Vapor Standards for Performance Evaluation of Combustible Gas Detectors

摘要

Calibration mixtures of hydrocarbon vapor were prepared for the calibration and performance evaluation of portable combustible gas detectors which are used to detect the presence of accelerant vapors in cases of suspected arson. The standards contained vapors of aliphatic and aromatic compounds common to petroleum distillates such as gasolines, which are frequently employed as accelerants in arson fires. These standards were prepared by a dynamic dilution technique in which the vapor evolving from diffusion tubes containing liquid hydrocarbons was diluted with air. The concentrations of the vapors were calculated from gravimetrically determined diffusion rates of the hydrocarbons and from measured flow of air at three temperatures: 30, 50, and 70C. Gas chromatographic analyses of the vapor-air mixtures generated at 30 and 50C showed that the vapor concentrations are essentially constant within measurement periods of 1 to 3 d and from one period to another, and that they agreed with calculated concentrations.