Early Warning for Combustible Gas Hazards

Methane (CH₄) is a widely used fuel gas and a significant explosion risk when released into enclosed or confined spaces. Monitoring methane as a percentage of the Lower Explosive Limit (LEL) is critical for preventing fires and explosions. Alphasense offers both catalytic and infrared methane sensors to meet different safety and performance requirements.

Sensor Product Overview

Portable and Fixed Gas Safety Instruments

• CH-A3 – Catalytic Methane Sensor The CH-A3 is a catalytic bead sensor designed for LEL methane detection in safety-critical applications. It provides a fast response to combustible gases and is widely used in portable and fixed gas detectors.


• IRM-AT – Infrared Methane / LEL Sensor The IRM-LEL uses infrared absorption to measure methane concentration relative to LEL. Unlike catalytic sensors, it does not consume oxygen and is resistant to poisoning, making it ideal for harsh or low-oxygen environments.

Choosing the CH₄ / LEL Right Sensor by Application

General Industrial Safety

• CH-A3 offers a cost-effective solution for standard methane detection.

Harsh or Low-oxygen Environments

• IRM-AT provides stable performance without catalytic degradation.

Long-life, Low-maintenance Systems

• IRM-AT minimizes calibration drift and poisoning risks.

Key Benefits Across the CH₄ / LEL Sensor Portfolio

• Proven methane detection technologies
• Options for catalytic or infrared sensing
• Designed for safety-critical deployment

Why OEMs Choose Alphasense

Alphasense methane sensors offer application-matched technology choices, enabling OEMs to balance cost, durability, and performance in gas-safety instruments.

How Methane / LEL Sensors Work

Pellistor methane sensors detect combustible gas by oxidizing small amounts of methane on a catalyst-coated “active” bead. As the gas burns on the bead’s surface, the bead heats up, causing its electrical resistance to rise. A second “reference” bead, built identically but without a catalyst, does not react with methane.

Both beads sit in a Wheatstone bridge circuit, which measures the difference in resistance. That differential change is directly proportional to methane concentration.

Because the technology relies on combustion, pellistors need sufficient oxygen—typically 10–12% O₂—to operate correctly. They cannot function in inert or oxygen-depleted environments such as nitrogen-purged spaces.

The result is a rugged, fast-responding LEL sensor widely used in portable and fixed industrial safety instruments.

Infrared LEL sensors use non-dispersive infrared (NDIR) absorption to measure methane without consuming gas or requiring oxygen. Methane absorbs IR energy at specific wavelengths; by directing IR light through an optical cavity and monitoring how much is absorbed, the sensor can determine methane concentration with high stability.

Alphasense NDIR methane sensors use dual-channel detection:

• An active channel filtered at a methane-specific absorption wavelength.


• A reference channel filtered at a wavelength not absorbed by methane.

Comparing these channels compensates for source drift, contamination, and aging—resulting in a highly stable, non-consumptive methane measurement method. Unlike pellistors, IR sensors operate reliably in low-oxygen or inert atmospheres and are resistant to poisoning, making them ideal for long-term monitoring, process environments, and applications with variable O₂ levels.

Why Measure Methane / LEL

Monitoring methane protects against:

• Explosions and fires
• Equipment damage
• Regulatory non-compliance
• Worker injury and loss of life