First of all, let's popularize the alarm value of the combustible gas alarm system, set it as: the default low limit is 25% LEL (5% LEL ~ 40% LEL is adjustable); the default high limit is 50% LEL (10% LEL ~ 100 %LEL adjustable).
The measuring range of the combustible gas alarm is 0~100%LEL. According to the national regulations, the low alarm is generally set between 15%LEL~25%LEL, and the high alarm is generally set to 50%LEL. Most of the current combustible gas alarms The low alarm point is set to 25% LEL. The 100% LEL here refers to the explosion limit value of the gas, that is to say, when the flammable gas alarm displays 100% LEL, the lower explosion limit of the flammable gas has just been reached.
Now you need to know which gas the tested combustible gas belongs to. Common ones are methane, isobutane, propane, hydrogen, benzene, ketones, alcohols, etc. Next, determine the concentration of the gas to be tested. Generally, the lower explosion limit (%LEL) is detected in most cases. Note: The lower explosion limit of different gases is different, such as 1.8% for isobutane and 5% for methane. There are also some detectable ppm (one millionth) level, 1%=10000ppm. If it is %LEL, the range is 0-100%LEL; if it is ppm, it is generally 0-100ppm or 0-1000ppm.
What are the low and high reports based on?
We often see that the measurement range of flammable gas alarms (gas detectors) such as natural gas alarms and liquefied gas alarms is 0-100% LEL, so what does 0-100% LEL mean?
When the concentration of flammable gas in the air reaches its lower limit of explosion, we call the explosion danger of the flammable environment in this place as 100%, that is, 100% LEL. If the flammable gas content only reaches 10% of its lower explosion limit, we call the explosion hazard of the flammable environment at this place 10% LEL; the monitoring of flammable gas in the ambient air often directly gives the flammable environment danger degree, that is, the percentage of the content of the combustible gas in the air and its lower explosion limit: [%LEL]; therefore, this kind of monitoring is sometimes called "explosion test", and the monitoring instrument used is also called "explosion tester" .
The highest concentration of flammable gas in the air when it encounters an open flame is called the upper limit of explosion - "UEL" for short. English: Upper Explosion Limited.
Explosion limits are for flammable gases and are very important for the setting of gas alarms. Explosion limit is a very important concept, which has great practical significance in fire and explosion protection work. The explosion limit is generally expressed by the volume percentage of combustible gas in the air, or the weight percentage of combustible gas.
The explosion limit is the general term for the lower explosion limit and the upper explosion limit. The concentration of combustible gas in the air will explode only when the concentration of the combustible gas is at the lower explosion limit or the upper explosion limit, and no explosion will occur below the lower explosion limit or higher than the upper explosion limit.
The explosion limit of flammable gas is divided into upper explosion limit and lower explosion limit. Above the upper limit, the oxygen content in the mixture is insufficient, and it cannot cause combustion or explosion. Below the lower explosion limit, the content of combustible gas in the mixture is insufficient to cause combustion or explosion. The combustion and explosion of combustible gas are also related to the pressure, temperature, ignition energy and other factors of the gas.
The lower explosion limit is generally expressed in the unit %LEL. Fixed gas alarms usually have two alarm points: 10%LEL is a first-level alarm, and 25%LEL is a second-level alarm; portable detectors usually have a 25%LEL alarm. alarm point.
