How To Choose The Right LEL Gas Detector

Choosing the right gas detector is vital. We must choose the right product for our project or application; in this post, I will share some tips on choosing the right LEL gas detector.

What does LEL stand for in gas detection?

L.E.L. stands for the Lower Explosive limit of a combustible gas or vapor. It’s the lowest level at which a gas can ignite in the air in the presence of an ignition source. 

Gas flammability can be in three levels: below LEL, between LEL and UEL (Upper Explosive Limit), and above UEL.

When the gas is below LEL, it is too lean to explode. When the gas is between LEL and UEL, it means that the gas will explode in the presence of a fire source and Oxygen.

If the gas is above UEL, it is too rich to explode. The image below illustrates this.

lel meaning

What is UEL in gas detection?

 U.E.L (upper explosive limit) is the maximum level in air that a gas may ignite. Any amount of gas below the LEL or above the UEL will not combust because it is too lean or rich.

How does the LEL gas detector work?

Known combustible gasses have a determined LEL expressed as a volume %Vol. As detectable combustible gas increases, an LEL sensor will display a readout from 0 – 100% LEL.

For example, Methane has an LEL of 5.0% Vol in the air. When the volume of Methane has reached 2.5% Vol, we’ve reached the 1/2 way point or 50% LEL.

If volume rises to 5.0% Vol, the gas monitor will display 100% LEL, and combustion is imminent if conditions are right.

An easy way to discern %Vol and %LEL is that the former is essentially a measurement of “how much in the air,” and the latter assesses “how dangerous.”

How To Choose The Right LEL Gas Detector

To choose the right sensor for your application, consider the sensor technology, the gases to be detected, and the environment.

Sensor technology

LEL gas detectors use two main technologies: Catalytic Bead (Pellistor) Sensors and Non-dispersive Infrared (NDIR) Sensors.

Catalytic Bead (Pellistor) Sensors

Catalytic bead sensors use beads, also called pellet-resistors or pellistors, and historically have been the most common technology used for combustible gas detection.

Non-dispersive Infrared (NDIR) Sensors

Infrared sensors commonly detect less reactive gases, which cannot be detected using typical electrochemical cells (such as CO2 or hydrocarbons).

Instead of relying on a chemical reaction, infrared sensors determine the amount of gas present by measuring how much light the specific gas absorbs.

Which sensor technology to pick?

Catalytic bead sensors are cheaper, which is why they are very common. For most projects, this is the right sensor you need.

The downside of catalytic bead sensors is that they are susceptible to poisoning. If you work in an environment with silicon, you will probably have to replace them very often. In this case, Infrared Sensors are better.

Another issue is that catalytic beads need Oxygen to work, so if you are going to work in an inert environment, infrared sensors are the better option.

The gases to be detected

Infrared technology does not detect all flammable gases, including Acetylene and Hydrogen.

If you want your LEL gas detector to detect those gases, you will be better off picking a catalytic bead LEL sensor.

The environment

Catalytic bead sensors need at least 10% Oxygen to work. They will not work in an inert atmosphere ( the atmosphere with zero Oxygen). 

If you know the environment you will use, the detector has less than 10% Vol of Oxygen. I will recommend picking a detector with an NDIR sensor.

What are the best LEL gas monitors? 

There is not a single LEL gas monitor that can fit everyone. Instead, consider selecting a monitor suitable for your application and budget.

Fixed gas monitor

If you want a fixed LEL gas monitor, consider the Sensepoint XCD from Honeywell

Portable Single Gas LEL detector

I worked with Rae Systems’ gas detector, and if you are looking for a reliable single-gas LEL detection, the Toxic RAE Pro LEL is the best on the market.

Portable Multigas LEL detector

BW Technologies’ GasAlertMax XT II is the best solution for detecting LEL in a multigas portable detector.

You can buy the Max XT II from any Honeywell distributor, or you can buy it on Amazon.

max xt ii

Selecting any of the above monitors will be fine for most general contracting and compliance needs. 

FAQ: LEL Gas Detector

What is LEL in a gas detector?

L.E.L. stands for the Lower Explosive limit of a combustible gas or vapor. It’s the lowest level at which a gas can ignite in the air in the presence of an ignition source.

Is LEL the same in all gases?

The Lower Explosive Limit (LEL) varies from gas to gas, but it is less than 5% by volume for most flammable gases.

This means that a relatively low concentration of gas or vapor is required to produce a high risk of explosion.

What is a safe LEL level?

A LEL level of less than 10 %LEL is considered safe. Anything above 10 %LEL is considered hazardous, and your unit should be able to alert you via audible and visual alarms.

What does 100% LEL mean?

One hundred percent lower explosive limit (100% LEL) denotes an atmosphere where gas is at its lower explosive limit. 

How do LEL sensors work?

The most common LEL sensor is a catalytic bead sensor. It detects gas through catalytic oxidation.

The heart of a catalytic bead sensor is the Wheatstone bridge circuit formed by the two catalytic beads. One is used as a reference, and the other is active.

Voltage is applied to this active bead, heating it to a point that readily sustains combustion.

As detectable gas is introduced, the active bead heats up even more, causing a measurable change in electrical resistance. This linear response becomes the LEL% reading on your meter.

Key Takeaways: How to choose the right LEL gas detector

Choosing the right LEL gas detector depends on factors like the technology you want to use.

There are two main technologies for LEL sensors: Catalytic Bead (Pellistor) Sensors and Non-dispersive Infrared (NDIR) Sensors.

For an Inert atmosphere, choose a detector with an Infrared sensor; if you want to detect most combustible gases, including Hydrogen and Acetylene, choose a gas detector with a catalytic bead sensor.

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