1. Role and performance of the detection system

1.1 Reminder of the main flammable properties of gases and vapors

Knowledge of the main properties of flammable gases and vapors is essential for the correct installation of gas detectors. A mixture is said to be flammable when it can propagate a flame. A flammable mixture consists of a fuel gas (or mixture of) and an oxidizing gas (or mixture of). For a mixture to be flammable, the fuel gas(es) must be present in a certain proportion in the mixture. The lower explosive limit (LEL) is the minimum concentration of fuel that can be ignited. Similarly, the upper explosive limit (UEL) is the maximum concentration of fuel gas that can be ignited. Figure 1 illustrates these concepts....