Flammability limit

Mixtures of flammable gases, vapors or dusts with that contained in atmospheric oxygen are explosive at certain mixing ratios. The area of summarizing all explosive mixture ratios is described by two explosion limits, the upper and lower explosive limit (UEL and LEL ). These limits are referred to as ignition limits.

It is the area below the lower explosion limit, in which the concentration of the flammable substance is too low, as lean mixture. The area above the upper explosive limit is called a rich mixture. Here the concentration of the flammable substance is too high to explode. However, a rich mixture may be further diluted in an air stream, and thus are under the OEG, which may lead to an explosion again.

The explosion limits are temperature and pressure dependent. For dusts in addition, the particle size and particle size distribution of the solid material has an effect on the explosion limits.

If the concentration of the flammable substance is in the air within explosion limits, the mixture is referred to as an explosive atmosphere.

The concentration of the flammable gas or vapor (not only in the explosion limits ) in volume - given %, mol% or g / m³, with the following relationship holds for ideal gases: 1 vol - % = 1 mol - % = 10,000 ppm

The following table shows the lower and upper explosion limits are specified for some gases when mixed with air. Other numerical values ​​are given in Table works and for some substances in the safety data sheets.