What is the appropriate setting for the combustible gas alarm value

What is the appropriate setting for the combustible gas alarm value

What is the alarm value of combustible gas? How to set the alarm value of combustible gas?

First let’s briefly understand %LEL and %VOL

%LEL: The lower explosion limit unit of the gas, such as 10%LEL refers to 10% of the lower explosion limit concentration of the gas. The lowest concentration of combustible gas in the air when it encounters an open fire is called the lower explosion limit—abbreviated as %LEL.

%VOL: Refers to the gas volume percentage, which has the same meaning as PPM, except that this unit is used when expressing high concentrations, 1%VOL=10000PPM; for example, 5%VOL refers to the volume of a specific gas in the air accounting for 5 %.

Alarm value setting of combustible gas alarm system:

The measurement range of combustible gas alarm is 0-100%LEL. According to national regulations, the low alarm is generally set to alarm between 15%LEL-25%LEL, and the high alarm is generally set to 50%LEL alarm. Most of the current combustible gas alarms The low alarm point is set to 25%LEL.

For example: the lower limit of explosion of natural gas is 5% volume ratio, that is to say, divide this 5% volume ratio into one hundred equal parts, so that 5% volume ratio corresponds to 100%LEL, that is, when the detector value reaches 10% At the LEL alarm point, it is equivalent to that the natural gas content is 0.5% volume ratio at this time. When the detector value reaches the 25%LEL alarm point, it means that the natural gas content is 1.25% by volume.

When the concentration of flammable gas reaches 100% LEL, an explosion will occur when encountering an electric spark. The lower limit of explosion of different gases is different, for example, hydrogen 4% VOL = 100% LEL, methane 5% VOL = 100% LEL

For example, the lower explosion limit of methane is 5%VOL, so 10%LEL of methane gas has the following corresponding relationship: 10%LEL=5000ppm=0.5%VOL