Even with a combustible gas channel on the same portable detector, selection cannot follow the same approach for hydrogen-handling sites and methane systems. If equipment is changed to an infrared sensor but the gas requiring detection is outside that sensor's targets, other equipment advantages cannot close the gap.
Compare portable gas detector infrared and catalytic sensors after first confirming detectability of the target gas and oxygen conditions. This article explains how to make a gas-specific selection table without extending infrared oxygen independence or catalytic broad gas response into superiority at every site.
1. List target substances before the combustible channel name
Combustible gas measurement does not concern just one gas. Identify system feedstocks, products, and residues, then list the gases and vapors requiring measurement. If mixture composition may change, record that possibility too.
Add the measurement objective: personal alarms, remote sampling before entry, or high-concentration process analysis. Different objectives can require different ranges, sampling devices, and verification methods. Using portable personal safety equipment for process analysis not permitted by the manual requires separate review.
Manufacturers distinguish sensor principles such as infrared, catalytic, and electrochemical and advise selection by target gas and application. The shared name “combustible sensor” does not imply an identical detection scope. Dräger sensor principles and selection guidance
2. NDIR measures specified infrared absorption
Non-Dispersive Infrared (NDIR) uses gas absorption of light in a specified wavelength region. Actual detectable substances vary with sensor wavelength, construction, and settings, so do not expand the scope to “infrared measures all hydrocarbons.”
Typical combustible gas NDIR sensors cannot directly detect hydrogen. Honeywell Impact series operating instructions also specify this limitation for combustible infrared sensors. Where hydrogen is expected, check whether the instrument separately includes an appropriate hydrogen-detecting sensor. Honeywell Impact operating instructions
NDIR's ability to measure a target gas without oxygen does not mean people are safe in an oxygen-deficient location. Oxygen concentration and toxic hazards require separate channels and management measures. Do not infer from one infrared characteristic that every sensor in an instrument is usable in an inert atmosphere.
Certain infrared configurations provide two gas channels simultaneously, but those functions are specifications for the exact sensor type and permitted gases. Do not generalize one product's multiple-channel capability to other infrared detectors.
3. For catalytic sensors, check combustion reactions and oxygen conditions
Catalytic sensors are also called catalytic combustion or catalytic bead sensors. They read changes from combustible gas oxidation as signals, so reliable response may be difficult in atmospheres with insufficient oxygen. Consult the sensor and manufacturer manual for specific minimum oxygen conditions.
OSHA technical material explains limitations of oxygen-dependent combustible sensors and the need to review manufacturer correction information when measuring gases other than the calibration gas. This is US technical guidance, not Korean legal criteria or identical settings for all equipment. OSHA technical material on direct-reading equipment
Exposure history to substances affecting catalytic sensors, including silicones, also matters. Normal operation yesterday does not prove today's sensitivity. Manage improper maintenance and sensor poisoning risks through pre-use verification and inspections following manufacturer instructions. OSHA direct-reading equipment testing guidance
Likewise, the statement that catalytic sensors can respond to hydrogen does not mean every catalytic sensor is suitable at every concentration and in every environment. Check hydrogen performance, calibration conditions, and operating scope in the individual sensor specifications. Distinguish what a principle can do from an actual instrument's approved measurement function.
4. Retain “unverified” in the gas-specific selection table
The table below gives an information-gathering sequence rather than product recommendations or certification determinations. Link each row to the relevant manufacturer's sensor part number and current documentation to make an actual selection table. Do not assume that changing gases requires only changing a correction factor.
Site condition | Infrared review question | Catalytic review question | Required finding |
|---|---|---|---|
Methane is the target | What methane range and settings does this sensor have? | What methane calibration and display conditions apply? | Suitability in the target concentration interval |
Hydrogen may be present | Is there a separate hydrogen detection channel? | Are hydrogen performance and use conditions specified? | A configuration without detection gaps |
Oxygen may be deficient | Is oxygen-free target gas measurement permitted? | How do oxygen conditions affect response? | Sensor limitations and separate oxygen management |
Multiple gases and vapors coexist | Is each substance included in the detection targets? | What gas-specific responses and calibration bases apply? | Separate assessment of undocumented substances |
Possible silicone or similar exposure | What limitations, such as optical contamination, apply? | What poisoning and sensitivity-loss management instructions apply? | Inspection and return-to-service procedures |
If a substance cannot be verified, do not arbitrarily mark it measurable. Provide substance names and mixture conditions to the process risk specialist and manufacturer and request further assessment. Where a substance cannot be detected, first verify whether changing sensor settings can actually resolve the problem.
5. Different calibration and actual gases change the meaning of numbers
Interpreting a combustible channel's percentage of lower explosive limit (%LEL) requires knowing its gas and reference basis. Even if a methane-calibrated instrument responds to another gas, do not assume the indication equals that gas's actual %LEL. Check the manufacturer's specified calibration method and correction information.
Mixtures require greater care. Do not apply one gas's correction factor to an entire mixture of unknown constituents and proportions to establish its concentration. Correction tables interpret measurements under their specified conditions; they do not create detection of gases a sensor cannot detect.
For models displaying both %LEL and vol% or switching ranges, consult individual manuals too. Do not interpret a lower number as reduced danger. For units and special states, see measurement range and accuracy specifications.
6. Hypothetical case: moving methane-focused equipment to a hydrogen process
Suppose a hypothetical facility team wants to deploy an infrared combustible channel instrument used for methane pipe checks at hydrogen-handling equipment. The first question is not runtime or sensor life, but whether it has a channel that directly detects hydrogen. Without one, an existing instrument reading 0 provides no evidence of hydrogen absence.
The team obtains sensor configuration tables for each instrument and the application scope of hydrogen channels. For a catalytic candidate, it reviews oxygen conditions and expected poisons as well as hydrogen detection performance. If oxygen deficiency is also expected, it does not select based only on catalytic hydrogen response, but reconsiders measurement methods valid under those conditions.
Nor does it use a CO channel's hydrogen cross-response for hydrogen safety monitoring, because interference differs from reliable quantitative measurement of a target substance. Review this distinction with electrochemical sensor specification comparisons. This hypothetical case explains equipment reassignment decisions, not a particular company's performance record.
7. Inspection systems remain necessary after selection
Even after selecting the sensor method, actual gas entry and alarm operation need verification. Although infrared may be less affected by catalytic poisons, optical and inlet contamination, equipment faults, and incorrect settings do not disappear. Do not reinterpret “resistant to poisoning” as “functional checks unnecessary.”
Connect target gases, calibration bases, and settings in equipment registers so they can be compared again after sensor replacement or process changes. Distinguish functional checks and calibration according to manufacturer manuals and record the required results. The pre-use checklist can support pre-use inspection forms.
Action checklist
[ ] Record expected gases and vapors and possible mixture changes by process.
[ ] Confirm combustible channel sensor types and part numbers.
[ ] If hydrogen is expected, separately confirm a configuration capable of direct detection.
[ ] Compare gas-specific infrared detectability using manufacturer information.
[ ] Review catalytic oxygen conditions and poisoning substances.
[ ] Record calibration gases, display references, and correction information conditions.
[ ] Do not mark unverified gases or operating conditions suitable.
[ ] Require sensor configuration review upon equipment reassignment and process changes.
Conclusion
Selecting infrared or catalytic sensors for portable gas detectors starts by comparing target gases and oxygen conditions. Omitting NDIR hydrogen detection limitations or catalytic oxygen dependence can leave important detection gaps.
Retain a table connecting gas-specific detectability, calibration bases, and maintenance conditions so decisions continue through equipment changes. Evidence from individual specifications under site conditions should determine selection rather than general advantages of a sensor method.
Sources
Dräger, Gas Detection Sensors — Sensor operating concepts and application-based selection.
Honeywell Analytics, Impact / Impact Pro / Impact Pro IR Operating Instructions — Infrared hydrogen detection limitations and operating conditions for the equipment.
OSHA, Technical Manual, Section II Chapter 3 — Combustible sensor oxygen dependence and differences between calibration gases and response. US technical guidance.
OSHA, Calibrating and Testing Direct-Reading Monitors — Manufacturer-guided testing and calibration and exposure factors affecting sensors. US guidance.