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Abstract

A method of detecting the presence of a foreign gas in a gaseous medium of known combustion properties uses the fact that the percentage lower or upper explosive limits (LEL or UEL) of mixtures of any flammable gas in any other gas all have approximately the same varying relationship to the percentage LEL or UEL of the mixture as a whole when a known percentage of a reference gas of known combustion properties is added to the mixture. The method comprises the steps of mixing a sample of a possibly contaminated gaseous medium with known combustion properties in a fire-safe container (12), actuating ignition means (17) in an attempt to ignite the gaseous mixture in the container (12), and using detection means (18) to detect ignition or otherwise of the gaseous mixture to enable the presence of a foreign gas above a predetermined concentration in the gaseous medium to be detected. Apparatus for use in this method comprises in combination with the fire-safe container (12), means (15) for introducing the sample of possibly contaminated gas into the container, valve means for introducing a known quantity of the reference gas into the container, and ignition and detection means (17,18) to permit and monitor attempts at ignition of the sample.

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First Claim