LEL (Lower Explosion Limit) monitor or a combustible gas monitor is a very vital aspect in hot work safety. Failure in doing an accurate LEL monitor will bring to a catastrophic condition.
The same condition will also happen when you use an improperly calibrated LEL meter or LEL detector, which is used to measure the LEL percentage of combustible gas or vapor in the atmosphere.
Before doing LEL monitor or operating an LEL meter, you should know exactly the following facts. They will help you with how to do the LEL monitor properly.
- The manufacturer’s manual is your main reference in operating your unit properly. Always refer to it for special instructions on operating your LEL meter.
- It may come with a single sensor for detecting a specific individual gas. Or it may contain a combination of sensors that is able to detect a variety of gases like oxygen, combustible gas (LEL), hydrogen sulfide, and carbon monoxide.
- LEL sensors are solid-state catalytic sensors, which are composed of two porous ceramic beads (active and inert beads) surrounding a coiled wire.
- Most LEL meters will respond to all combustible gas exposure since most LEL sensors are non-specific.
- The indicated value will be based on the LEL of the calibration gas.
- If an LEL meter is used to measure combustible gas LEL other than combustible gas used for calibration, the indicated value will be lower or higher than it should be. The manufacturer usually provides LEL correlation factors to calculate the measured gas LEL based on calibration gas.
- The measured value that you see on the LEL meter-monitor is the percentage of LEL of combustible gas. Meanwhile, LEL is declared as a percentage of combustible gas concentration in the atmosphere.
- LEL sensor is usually guaranteed for one or two years. Ensure the guarantee period of your LEL sensor.
- LEL sensors have operating temperature limitations. Please refer to the manufacturer’s manual.
- There are many factors that can shorten the lifetime of your LEL meter sensor such as dropping the sensor that causes the fine wire inside to break.
- A combustible gas-rich but lacking oxygen atmosphere can cause the LEL meter sensor lifetime short. It is due to a build-up of carbon, unburned gas, and tar on the active bead.
- Periodic calibration of the LEL meter should always be done according to the manufacturer’s instructions. Keep the calibration record properly and indicated the calibration status clearly on the unit.
- A bumping test is recommended to be performed prior to each use of the unit by most manufacturers to check that the gas detector is in good condition. Bumping test is done by exposing the unit to a certain gas concentration.
- The bumping test does not replace the need for periodic calibration.
- An audible alarm is set at 10% of LEL as stated in OSHA standard 29 CFR 1910.146.
- Workers who use the unit have to be trained well and the training is documented.
- When you see zero reading of LEL on the monitor, it does not mean that there is no combustible gas in the atmosphere. It may only mean that the gas exists at a low concentration which is below the detectable limits of the LEL meter.
- In the case of an LEL monitor in a confined space, combustible gas LEL must be evaluated in four-foot intervals in every direction of travel.
- LEL monitor has to be done before and during a hot work is done.