Lower and upper explosive limit measurement
What is the lower and upper explosive limit?
The explosive nature of the mixture between air and a compound depends on the concentration of the latter. The minimum gas/vapour/solid concentration for the mixture to be explosive defines the lower explosive limit (LEL). Below this concentration, the mixture is therefore not explosive.
The upper explosive limit (UEL) corresponds to the value of the concentration above which the mixture has too much fuel but not enough oxidizer to allow combustion. Above this limit, the mixture is no longer explosive.
These two values make it possible to define the explosive range of a compound. They are expressed in % of volume in the air for vaporized gases and liquids, while they are expressed in g/m3 for solid fuels.
Temperature and pressure are parameters that influence LEL and LSE values. These two parameters tend to widen the explosive range.
In the case of solids, humidity and particle size also affect explosiveness.
Why measure the lower and upper explosive limits?
The determination of lower and upper explosive limits are essential in the field of safety. This particularly concerns so-called ATEX zones (explosive atmosphere). They are therefore obviously required for the constitution of the SDS (Safety Data Sheets). These values thus allow safe handling of volatile chemicals.
- Use of a neutral gas (nitrogen, argon) or an absorbent resin
- Reduction of the percentage of combustible vapour/gas in the air through optimized ventilation
- Continuous monitoring of the vapour/gas rate using an explosimeter placed in a high-risk area.
How to measure LEL and LSE?
The LEL and LSE measurements offered by Calnesis are carried out according to the ASTM E681 standard. They are made in a pressure chamber. This equipment allows measurement over a temperature range not exceeding 150°C. A lower pressure limit is set at around 13 kPa (ie 100 mmHg) to control the danger of explosion while preventing the explosive range from disappearing. This method is based on electrical ignition and visual observations of product ignition analyzed by flame propagation.