Gas Detector Sensor Types Explained: Catalytic, Infrared, and Electrochemical Options for NZ Workplaces

A gas detector is only protective when its sensor can detect the hazard that may actually be present. Selecting the wrong technology can leave workers exposed, even when a monitor appears to be operating normally.

This guide explains the main gas detector sensor types used in New Zealand workplaces: catalytic, infrared (IR) and electrochemical. It covers practical selection, bump testing and calibration for confined spaces, plant rooms, wastewater sites and industrial processes.

This overview gives safety managers, engineers and operators a clear way to compare sensor technologies before selecting portable or fixed gas detection equipment.

Catalytic Sensors and LEL Gas Detection

Catalytic sensors, often called pellistor sensors, are among the longest-used options for combustible gas detection. They warn workers when flammable gas or vapour reaches a percentage of its Lower Explosive Limit, or %LEL.

For many NZ workplaces using LPG, natural gas, petrol vapours, solvents or hydrocarbons, a catalytic LEL sensor remains a practical and cost-effective option. It does not suit every flammable-gas situation.

A catalytic sensor oxidises combustible gas on a heated sensing element. This changes its temperature and electrical resistance. The detector converts this change into a gas reading, usually shown as %LEL.

Where catalytic gas sensors work well

• Oxygen is present in the air
• The main hazard is a combustible hydrocarbon gas or vapour
• The detector is calibrated for, or correctly adjusted for, the expected gas
• Sensor poisons or inhibitors are unlikely to be present
• Your equipment receives regular bump tests and calibration

Common uses include boiler rooms, LPG storage areas, fuel-handling locations, workshops and general industrial maintenance work.

Important catalytic sensor limitations

Catalytic sensors need oxygen to work correctly. In a confined space, vessel or pit with low oxygen, your detector can under-read a flammable gas hazard or fail to respond as expected.

Certain substances can poison or inhibit the sensing bead. These include:

• Silicone-based sprays, sealants and lubricants
• Sulphur compounds
• Leaded vapours
• Certain chlorinated substances
• High concentrations of combustible gas

This matters in maintenance areas. Your detector can appear to work during a routine check, then become less responsive after repeated contact with contaminants.

Common mistake: Do not assume a catalytic sensor measures every flammable gas with full accuracy. Most catalytic sensors use a reference gas for calibration, often methane or pentane. Readings for a different gas or vapour can vary. Check correction factors and manufacturer data.

Before choosing combustible-gas monitoring equipment, confirm which gases and site conditions apply. You can then review suitable personal gas monitors and gas detection equipment.

Infrared Sensors for Hydrocarbon Gases

Infrared gas sensors, often called IR sensors, measure gases which absorb infrared light at specific wavelengths. They are widely used for hydrocarbon and carbon dioxide detection, especially where catalytic sensors face poisoning risks or low-oxygen conditions.

When you compare IR and catalytic gas detectors, IR technology often suits enclosed process areas, offshore-style environments, wastewater facilities, fuel systems and locations where hydrocarbon leaks are a credible risk. It is not a replacement for catalytic LEL detection in every setting.

An IR sensor passes infrared light through a measurement path. A target gas absorbs some of this light. The detector then calculates gas concentration.

Key advantages of infrared gas detectors

• They do not need oxygen to measure target gases
• They are generally more resistant to catalytic poisons, including silicones
• They suit many hydrocarbon applications
• They can provide a longer sensor life in some settings
• They can measure carbon dioxide, depending on instrument and sensor setup

For NZ workplaces, IR technology is useful where low-oxygen conditions are possible. Examples include enclosed process equipment, some tank and vessel work, biogas systems, or places where gas displacement is a risk.

IR gas detector limitations to check before specifying

Infrared technology does not detect every combustible gas. Hydrogen is the key example. Hydrogen does not absorb infrared light in a way conventional IR combustible-gas sensors need.

Some other gases give a weaker response, need a different sensor setup or require a specific calibration method. Do not select an IR detector because it seems newer than a catalytic detector.

Pro tip: When you compare catalytic and IR gas detectors, start with one practical question: “What exact gas or vapour do we need to detect?” Your answer needs to guide sensor selection, rather than a standard detector setup used at a different site.

If your task involves flue gas, combustion efficiency or carbon monoxide measurements, use of a dedicated combustion and flue gas analyser can be more suitable than a general four-gas monitor. View combustion and flue gas analysers.

Electrochemical Gas Sensors for Toxic Gases and Oxygen

Electrochemical sensors commonly monitor toxic gases and oxygen levels. They form a central part of personal and fixed gas detection systems used in confined spaces, wastewater plants, refrigeration areas, laboratories and industrial process environments.

Unlike a combustible-gas sensor, an electrochemical sensor usually targets one specific gas. Your monitor can combine several sensor types, such as oxygen, hydrogen sulphide, carbon monoxide and %LEL detection.

Electrochemical sensors use a chemical reaction to produce an electrical signal when target gas reaches the sensor. The detector converts this signal into a concentration reading. Toxic gas readings are usually shown in parts per million, or ppm. Oxygen readings are usually shown as percentage by volume.

Common electrochemical sensor applications

• Oxygen, or O₂: Detecting oxygen depletion or enrichment
• Carbon monoxide, or CO: Common near combustion equipment, generators and vehicle exhaust
• Hydrogen sulphide, or H₂S: A serious risk in wastewater, sewer, effluent, pulp and biogas-related work
• Ammonia, or NH₃: Relevant in refrigeration plant rooms, cold stores and chemical handling
• Chlorine, or Cl₂: Used in some water treatment and chemical dosing work
• Sulphur dioxide, nitrogen dioxide and other specified toxic gases: Selected according to your workplace process

Why oxygen monitoring matters in confined spaces

Oxygen is more than another reading on a multi-gas detector. Low oxygen can affect judgement and physical ability. It can affect how well catalytic combustible-gas sensors work too.

High oxygen levels increase fire risk. Materials ignite more easily and burn with greater intensity. Consider oxygen monitoring alongside toxic and flammable-gas risks, rather than using it in place of them.

A common NZ confined-space error is relying on a standard four-gas monitor without checking whether it covers your real process risk. For example, a wastewater site can need H₂S monitoring, while a refrigeration plant room can need ammonia detection. A four-gas setup is useful when its sensors match your site’s credible hazards.

Electrochemical sensor limitations

Electrochemical sensors have a limited working life. Their performance can be affected by:

• Changes in temperature and humidity
• Cross-sensitivity to other gases
• Sensor drift over time
• Exposure to high gas concentrations
• Storage conditions and instrument age

Having a sensor fitted in a detector does not mean it suits your task. Check safety data sheets, process chemicals, maintenance work, nearby plant and credible upset conditions before choosing a sensor.

If your work involves volatile organic compounds, assess whether you need a dedicated VOC gas detector. VOC measurement often needs different technology, such as photoionisation detection, or PID, rather than a standard electrochemical sensor. View VOC gas detectors.

Choosing Gas Detector Sensor Types for NZ Workplaces

The best gas detector sensor type depends on hazards where people work, rather than the most common detector model. Your documented hazard assessment needs to identify possible releases, people at risk and changing conditions during normal work, cleaning, maintenance or emergencies.

For Auckland and wider New Zealand sites, practical conditions vary widely. Coastal humidity, wastewater gases, refrigeration systems, LPG, diesel exhaust, enclosed plant rooms and seasonal maintenance shutdowns can all affect sensor selection and maintenance needs.

Start with the gas hazard, not the instrument

Before selecting a portable or fixed gas detector, answer these questions:

• Which gases, vapours or oxygen conditions can occur? Consider raw materials, by-products, cleaning chemicals, combustion gases and process upsets.
• Can oxygen be displaced, used up or enriched? This is important in confined spaces, vessels, pits, tanks and enclosed rooms.
• Is the gas flammable, toxic, asphyxiating, or more than one of these? For example, methane brings flammability and oxygen-displacement risks. Hydrogen sulphide is toxic and flammable.
• Are sensor poisons present? Silicone sprays, solvents and certain chemicals can affect catalytic sensors.
• Do workers need personal protection, area monitoring, or both? A personal monitor protects its wearer near a hazard. A fixed gas detection system can give early warning, control ventilation, trigger alarms or connect with plant controls.
• Which environmental conditions will your instrument face? Consider heat, cold, moisture, dust, vibration, water ingress and chemical exposure.

Typical gas detection examples in New Zealand

Wastewater treatment and sewer work

Likely gas hazards: H₂S, methane, oxygen depletion and CO₂.

Sensor types often considered: Electrochemical H₂S and O₂, catalytic or IR LEL, plus CO₂ where required.

Refrigeration plant rooms

Likely gas hazards: Ammonia and oxygen displacement.

Sensor types often considered: Electrochemical NH₃ and O₂, based on your risk assessment.

Boiler rooms and combustion work

Likely gas hazards: CO, fuel gas and oxygen.

Sensor types often considered: Electrochemical CO and O₂, plus a catalytic or IR combustible-gas sensor.

Confined-space entry

Likely gas hazards: Oxygen depletion, CO, H₂S and flammable gases.

Sensor types often considered: A multi-gas monitor matched to your entry permit and process hazards.

Fuel storage and maintenance workshops

Likely gas hazards: Petrol vapour, LPG, natural gas and CO.

Sensor types often considered: Catalytic or IR LEL, plus electrochemical CO where relevant.

Biogas and anaerobic digestion

Likely gas hazards: Methane, CO₂, H₂S and oxygen deficiency.

Sensor types often considered: IR or catalytic combustible-gas sensor, electrochemical H₂S and O₂, plus CO₂ measurement where required.

Common mistake: Do not treat a “four-gas monitor” as a risk assessment. A standard monitor often includes O₂, LEL, CO and H₂S. This does not mean it suits ammonia, chlorine, VOCs, carbon dioxide or every hydrocarbon.

Where a gas release links to process pressure, flow or level changes, combining gas detection with suitable instrumentation can improve early warning. Depending on your application, this can include pressure transmitters and transducers, flow meters, or level transmitters.

Bump Testing, Calibration and Ongoing Gas Detector Maintenance

Even a correctly selected detector can fail to protect workers if it is not tested, maintained and used correctly. Bump testing and calibration are essential controls, but they do different jobs.

A bump test checks whether your detector responds to gas and activates alarms. Calibration checks whether its displayed reading remains accurate against a known test-gas concentration.

What is a bump test?

A bump test is a functional test where you expose your detector to known test gas. It confirms:

• Gas reaches the sensor
• The sensor responds
• Audible, visual and vibration alarms activate
• The instrument responds within an acceptable time
• The pump and sampling path work correctly, where fitted

A bump test does not confirm full measurement accuracy. It is a quick operational check. Complete it at a frequency set by manufacturer instructions, site procedure and your risk assessment. In higher-risk work, this is often before use.

What is gas detector calibration?

Calibration compares your detector reading with a known concentration of calibration gas. If your instrument falls outside its accepted tolerance, it can need adjustment, servicing or sensor replacement.

Calibration frequency depends on manufacturer instructions, sensor type, operating environment, use level and site controls. A detector used every day in harsh wastewater or industrial work needs more attention than one kept in storage for occasional use.

Gas detector maintenance checklist

Before using a monitor, complete these checks:

• Confirm the sensor setup matches your work permit and hazard assessment
• Check your instrument is within its calibration due date
• Complete the required bump test
• Inspect filters, pump tubing, water traps and sample probes
• Check battery charge and alarm operation
• Confirm you have correct calibration and bump-test gas
• Check sensor expiry dates and service records
• Ensure workers understand alarm actions, evacuation procedures and fresh-air requirements

Pro tip: Calibration gas has its own expiry date, concentration and storage requirements. Incorrect gas, an expired cylinder or an incorrect regulator can weaken your test process.

For organisations needing traceable calibration support, Teltherm supplies calibration gas and provides an IANZ-accredited calibration laboratory. Confirm service scope against your instrument type, manufacturer requirements and site procedures.

Frequently Asked Questions

Choosing gas detection equipment often raises questions which sensor type alone cannot answer. Your gas, location, task and operating conditions all matter.

These answers offer a practical starting point. Check them against manufacturer documents, safety data sheets and your site-specific risk assessment.

Is infrared better than a catalytic gas detector?

Neither is always better. IR sensors often suit many hydrocarbons in low-oxygen settings or locations where catalytic poisoning is likely. Catalytic sensors remain useful for many combustible gases and can detect hydrogen, which conventional IR combustible-gas sensors generally do not detect.

Your correct choice depends on gases present, oxygen conditions, contaminants and approved detector performance specifications.

What is the difference between a bump test and calibration?

A bump test is a functional check. It confirms gas reaches your sensor and your detector alarms respond.

Calibration checks measured-reading accuracy against a known gas concentration. It can involve adjustment where your detector falls outside manufacturer tolerance.

Which gases can electrochemical sensors detect?

Electrochemical sensors commonly detect oxygen, carbon monoxide, hydrogen sulphide, ammonia, chlorine and other specified toxic gases. In most cases, each target gas needs its own sensor.

Check cross-sensitivity too, especially where several gases or chemicals are present.

Can one gas detector detect every workplace hazard?

No. A standard four-gas monitor is useful, but it might not detect ammonia, chlorine, VOCs, carbon dioxide or every flammable gas and vapour.

Select your detector around your workplace hazard assessment. If you are unsure, review safety data sheets, process drawings, past incidents, maintenance work and confined-space entry requirements.

How often does a gas detector need calibration in New Zealand?

Follow your detector manufacturer’s instructions first. Then apply your site risk assessment and maintenance procedures. A suitable interval varies with sensor type, frequency of use, environmental conditions and consequences of detector failure.

A bump test often takes place more often than calibration.

Do gas detectors need calibration after exposure to high gas concentrations?

Potentially, yes. High gas exposure, sensor poisoning, physical damage, water ingress or a failed bump test can affect instrument performance. Remove your detector from service if it acts unexpectedly. Have it inspected, tested or calibrated before returning it to use.

Sources

• Teltherm gas detection equipment
• Teltherm personal gas monitors
• Teltherm calibration gas
• Teltherm IANZ-accredited calibration laboratory

A Practical Next Step for Your Site

Your choice between catalytic, infrared and electrochemical gas detector sensors starts with people who face exposure and gases they can encounter. Use a hazard-led approach. Identify gas, assess conditions, select suitable sensor technology and maintain it throughout its working life.

Before your next confined-space entry, plant shutdown or detector replacement, follow this simple process. List potential gases, check oxygen risks, identify sensor poisons, confirm required alarms and verify bump-test and calibration procedures. This gives your team a clearer basis for specifying equipment than choosing a standard monitor setup.

If you need support reviewing gas detector options, calibration gas or instrument servicing for an Auckland or New Zealand site, contact the Teltherm gas detection team. They can match suitable equipment and support services to your documented workplace hazards.