Portable Gas Detection for Industrial Safety: How NDIR Sensors Work

TL;DR: How portable gas detectors improve industrial safety

Portable gas detectors provide real-time monitoring of hazardous atmospheres where fixed gas detection systems cannot always provide adequate protection, particularly when workers move between locations or enter confined, remote or poorly ventilated areas.

Many modern portable detectors use non-dispersive infrared (NDIR) sensing in the mid-infrared (MIR) spectrum to identify gases according to their characteristic infrared absorption wavelengths.

Key considerations include:

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• Detecting hazardous gases close to the worker
• Providing real-time warnings as atmospheric conditions change
• Monitoring toxic, asphyxiant and flammable gas hazards
• Using NDIR technology for gases with suitable infrared absorption characteristics
• Matching infrared emitters and photodetectors to target gas wavelengths
• Achieving high sensitivity in compact portable devices
• Minimising power consumption to extend battery life
• Providing stable sensing with relatively low maintenance requirements
• Meeting requirements for equipment used in hazardous and explosive atmospheres
• Balancing sensitivity, size, cost and multi-gas capability

NDIR sensing is particularly useful for gases including carbon dioxide, methane and hydrocarbons but it cannot detect every hazardous gas, so sensor technology must always be selected according to the target gas and application.

Why is portable gas detection important for industrial safety?

Workers in industries such as oil and gas, mining, and emergency response frequently operate in hazardous environments where exposure to toxic or flammable gases can pose serious risks.

Confined or poorly ventilated spaces can allow dangerous gas concentrations to develop rapidly, creating potentially life-threatening conditions. Continuous monitoring is therefore essential to mitigate these safety risks and protect personnel.

Fixed gas detection vs portable gas monitoring

Fixed gas monitoring systems are widely used in industrial facilities, particularly in areas where hazards are well understood. However, they cannot always provide adequate protection when workers move between locations or operate in remote areas where permanent monitoring infrastructure is not practical.

Portable gas detection therefore complements fixed monitoring by providing protection that travels with personnel as they move between work areas or enter locations beyond the coverage of permanently installed sensors.

As a result, portable gas detectors and personal gas monitoring devices are increasingly being used to measure hazardous gas concentrations directly in the field.These handheld or wearable instruments provide real-time warnings when hazardous gases are detected, allowing workers to respond quickly to changing conditions.^1,2 

Modern portable detectors must combine compact size, long battery life, and high sensitivity to operate effectively in demanding environments where maintenance access may be limited.

Many of these devices rely on non-dispersive infrared (NDIR) sensing in the mid-infrared (MIR) spectral region, where numerous industrial gases exhibit strong absorption features. Combining MIR optical components with carefully engineered system design allows sensors to deliver reliable gas detection even under harsh operating conditions.

What hazardous gases must industrial gas detectors monitor?

Industrial processes frequently involve gases that can present serious safety hazards, and these generally fall into three categories: asphyxiant, toxic, and flammable.²

Asphyxiant gases and oxygen-deficient atmospheres

Asphyxiant hazards can arise when gases such as methane (CH₄) or nitrogen (N₂) displace oxygen within an enclosed atmosphere. Other gases such as carbon monoxide (CO) present serious toxic exposure hazards even at concentrations that do not significantly reduce atmospheric oxygen.^5,6

Toxic gas hazards in industrial environments

Toxic gases represent another major risk, and include substances such as carbon dioxide (CO₂), hydrogen sulphide (H₂S), and chlorine (Cl₂). Depending on concentration and exposure duration, these gases may lead to respiratory irritation, long-term health complications, or fatal poisoning.²

Flammable gases and explosive atmospheres

Flammable gases and vapours introduce an additional hazard because they can ignite or explode when mixed with air. These include hydrocarbons like methane (CH₄), propane (C₃H₈), and gasoline vapours, which are commonly encountered in industrial environments and may form explosive mixtures if concentrations exceed safe limits.^2,3 

How does optical gas sensing detect hazardous gases?

Real-time monitoring of hazardous gases requires sensing technologies capable of delivering accurate measurements under demanding conditions. Optical sensing techniques are widely used for this purpose because they enable non-contact measurement with fast response times and high selectivity.

How does an NDIR gas sensor work?

NDIR sensing is a popular option in which infrared radiation emitted from a light source passes through a chamber containing the gas sample, with a photodetector positioned on the opposite side to measure the intensity of the transmitted light.

Why is the mid-infrared spectrum used for gas detection?

Gas molecules absorb radiation at specific wavelengths corresponding to their molecular vibrational modes. When the target gas is present, absorption at this wavelength reduces the detected signal, and the magnitude of the reduction indicates the gas concentration.

The MIR spectral region is particularly well suited to gas sensing because many molecules exhibit strong fundamental absorption bands at these wavelengths.

Which gases can NDIR sensors detect?

Compounds such as CO₂, CH₄, and C₃H₈ can therefore be detected with high sensitivity using MIR-based NDIR sensors.⁴

Which gases cannot be detected using NDIR?

NDIR cannot detect every gas. Homonuclear molecules such as N₂ and Cl₂ do not exhibit suitable infrared absorption characteristics for conventional NDIR detection and therefore require alternative sensing technologies.⁵

What determines whether a gas can be detected using NDIR?

NDIR detection depends on whether the target gas absorbs infrared radiation strongly enough at a wavelength that can be measured by the sensor.

Different molecules exhibit characteristic absorption bands associated with their molecular vibrations. By selecting an infrared source and detector that operate around a target absorption wavelength, the sensor can measure how much infrared radiation is absorbed and use that change to determine gas concentration.

This makes wavelength selection fundamental to NDIR sensor design. However, gases without suitable infrared-active absorption features require other detection technologies such as electrochemical, catalytic or alternative optical sensing methods.

How are portable industrial gas detectors designed?

Battery life, size and reliability in portable gas detectors

Portable gas detectors must be compact, energy efficient and operate reliably in harsh environments with limited access or maintenance opportunities. One advantage of NDIR sensing is that it relies primarily on solid-state optical components rather than chemical reactions, meaning infrared emitters and photodetectors can operate for many years without degradation, providing stable performance over long periods with minimal maintenance.⁶

NDIR vs electrochemical gas sensors

Electrochemical sensors, by contrast, often require periodic calibration or replacement because the chemical sensing elements degrade over time.^4,7

How small can portable NDIR gas sensors become?

Recent advances in optical components have also enabled significant miniaturisation of NDIR gas sensors, some measuring less than 20 mm in length while still meeting strict industrial safety standards. 

Electrochemical sensors remain highly important for detecting many toxic gases that cannot be measured effectively using NDIR. The appropriate sensing technology therefore depends on the target gas, measurement range, required response characteristics, maintenance requirements and operating environment.

No single gas sensing technology can detect every industrial gas. Sensor selection must therefore begin with the target gas or gases, required concentration range, operating environment and response requirements before factors such as instrument size, power consumption and cost are considered.

ATEX and IECEx requirements for portable gas detectors

Equipment designed for hazardous environments must often comply with certification schemes such as ATEX (ATmosphères EXplosibles) and IECEx gas detection standards (International Electrotechnical Commission Explosive), along with performance standards including IEC 60079-29-1 and EN 45544.^8,9,10,11

Selecting MIR LEDs and photodetectors for NDIR gas sensing

Achieving reliable detection within such compact devices requires careful selection of optical components. In many high-performance designs, MIR light-emitting diodes (LEDs) are paired with indium arsenide antimonide (InAsSb) photodiodes. These detectors provide strong sensitivity in the 3-5 µm wavelength range and beyond, which corresponds to the absorption bands of several key industrial gases (Table 1).^12,13

Matching the emission wavelength of the light source with the absorption characteristics of target gases in this way improves measurement sensitivity while reducing interference from environmental factors, such as humidity or temperature fluctuations.¹⁴

Infrared absorption wavelengths of common hazardous gases

Table 1: Typical infrared absorption wavelengths for selected hazardous gases.^15,16

What are the main design trade-offs in portable gas detectors?

Although optical sensing technologies offer several advantages, engineers must balance multiple constraints when developing portable gas detectors.

Sensitivity vs cost and power consumption

Some lower-cost systems rely on alternative components – such as pyroelectric detectors, lead-salt sensors, or filament-based infrared emitters – which may reduce manufacturing costs, but can introduce trade-offs in response time, measurement precision, or power consumption.

Single-gas vs multi-gas detection

Another design consideration is whether a sensor should detect a single gas or multiple gases simultaneously. For example, many portable devices focus on detecting CH₄ because of its flammability risk.

How optical design enables multi-gas detection

Multi-gas detection systems are possible, but require additional optical channels or detectors, increasing system complexity, size, and cost.

However, advanced optical components can help to address some of these challenges. Multi-gas detection can be improved using more sensitive detectors with better signal-to-noise ratios, combined with higher output light sources, enabling the optical beam to be separated and measured across different gas channels more effectively.

The future of portable gas detection for industrial safety

Portable gas monitoring devices are becoming an increasingly important component of industrial safety systems. Advances in MIR optical technologies are enabling the development of compact sensors capable of detecting hazardous gases with high sensitivity while operating reliably in demanding environments.

As optical components and sensor designs continue to evolve, portable gas monitoring devices are expected to offer improved sensitivity, longer operating lifetimes, and expanded capabilities for detecting multiple gases within a single compact system, ultimately improving safety for workers operating in confined or remote hazardous environments.

As portable detectors become smaller and more capable, the key engineering challenge will remain selecting sensing technologies that match the gases, concentration ranges, environmental conditions and certification requirements of each application. No single sensing principle is suitable for every hazardous gas, making sensor selection and system design fundamental to reliable industrial safety monitoring.

References

1. United Safety. Fixed vs. Portable Gas Detection: Which One Do You Need? Published 10^th March 2025. Accessed 23^rd of July 2025 
2. Environmental XPRT. Unveiling the Importance of Portable Gas Detectors. Accessed 23^rd of July 2025. 
3. International Safety Equipment Association. Portable Gas Detection. Accessed 23^rd of July 2025. 
4. Sensor One Stop. Infrared (NDIR) Sensors, A Comprehensive Guide. Accessed 23^rd of July 2025. 
5. Wenzel, T. Introduction to Infrared Spectroscopy. Chemistry LibreTexts (2024). Accessed 4^th of April 2026. 
6. Gibson, D. & MacGregor, C. A Novel Solid State Non-Dispersive Infrared CO₂ Gas Sensor Compatible with Wireless and Portable Deployment. Sensors 13(6), 7079–7103 (2013). doi: 10.3390/s130607079. Accessed 4^th April 2026. 
7. Hamamatsu Photonics. Beyond Gas Sensing Panel Discussion. Accessed 23^rd of July 2025. 
8. European Commission. Equipment for potentially explosive atmospheres (ATEX). Accessed 4^th of April 2026. 
9. International Electrotechnical Commission Explosive (IECEx). Certified equipment scheme overview. Accessed 4^th April 2026.
10. International Electrotechnical Commission (IEC). IEC 60079-29-1: Explosive atmospheres – Gas detectors – Performance requirements of detectors for flammable gases. Accessed 4^th April 2026. 
11. British Standards Institution (BSI). BS EN 45544 series: Workplace atmospheres – Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours. Accessed 4^th April 2026. 
12. Hamamatsu Photonics. Gas analysis. Accessed 23^rd of July 2025 
13. Hamamatsu Photonics. NDIR gas sensing Improve your detector design. Accessed 23^rd of July 2025 
14. Hamamatsu Photonics. Beyond CO₂: the emerging importance of multi-gas detection. Accessed 4^th April 2026. 
15. Hamamatsu Photonics. Devices for Gas Measurement. Accessed 7^th of May 2026
16. NIST. Octane. Accessed 7^th of May 2026

Frequently Asked Questions about Portable Gas Detection

What is a portable gas detector?

A portable gas detector is a handheld or wearable instrument used to monitor the atmosphere around a worker for potentially hazardous gases. It can provide real-time measurements and alarms when gas concentrations reach dangerous levels.

Why are portable gas detectors used in industrial environments?

Portable gas detectors provide protection in areas where fixed monitoring systems may not offer sufficient coverage. They are particularly useful for workers moving between locations or entering confined, remote or temporary work areas.

What gases can portable gas detectors measure?

Depending on the sensing technology used, portable detectors can measure flammable gases, toxic gases and oxygen-deficient atmospheres. Common targets include methane, carbon monoxide, carbon dioxide, hydrogen sulphide and other industrial gases and vapours.

What is an NDIR gas sensor?

A non-dispersive infrared or NDIR gas sensor measures gas concentration by passing infrared radiation through a gas sample and detecting how much radiation is absorbed at wavelengths associated with the target gas.

How does NDIR gas detection work?

Gas molecules absorb infrared radiation at characteristic wavelengths. An NDIR sensor measures the reduction in transmitted infrared light at a selected wavelength and uses the amount of absorption to determine gas concentration.

Why is mid-infrared light used for gas sensing?

Many industrial gases have strong fundamental molecular absorption bands in the mid-infrared region. These strong absorption features allow suitable gases to be detected with high sensitivity.

Which gases can NDIR sensors detect?

NDIR sensors can detect gases that exhibit suitable infrared absorption characteristics. Common examples include carbon dioxide, methane, carbon monoxide and several hydrocarbon gases.

Can an NDIR sensor detect nitrogen?

Conventional NDIR sensing is not suitable for detecting nitrogen because N₂ does not exhibit the strong infrared-active absorption characteristics required for this measurement technique.

Can an NDIR detector detect chlorine?

Chlorine is not typically measured using conventional NDIR technology and requires an alternative sensing method suited to its molecular characteristics.

What is the difference between NDIR and electrochemical gas sensors?

NDIR sensors use optical absorption to determine gas concentration while electrochemical sensors generate an electrical response through a chemical reaction with the target gas. Each technology is suitable for different gases and operating conditions.

Do NDIR gas sensors require calibration?

Gas detection equipment still requires appropriate testing and calibration according to the manufacturer’s instructions and applicable safety procedures even where optical components offer good long-term stability. OSHA notes that proper testing, maintenance and calibration are important for maintaining the accuracy of direct-reading gas monitors.

What is the difference between fixed and portable gas detection?

Fixed detectors continuously monitor predetermined areas within a facility while portable detectors move with workers. Portable systems therefore help monitor temporary, remote or changing work locations that may fall outside the coverage of fixed detectors.

Why are portable gas detectors important in confined spaces?

Confined or poorly ventilated spaces can allow hazardous gas concentrations or oxygen-deficient atmospheres to develop rapidly. Portable detectors allow workers to monitor atmospheric conditions before and during entry.

What is a multi-gas detector?

A multi-gas detector simultaneously monitors more than one atmospheric hazard. Depending on its design, it may combine multiple sensors or optical channels to detect different gases within the same instrument.

What is ATEX certification for gas detectors?

ATEX refers to the European regulatory framework governing equipment and protective systems intended for use in potentially explosive atmospheres. Equipment within scope must satisfy the relevant requirements before being placed on the EU market.

What is IECEx certification?

IECEx is an international conformity assessment system for equipment and services used in explosive atmospheres. Its equipment certification scheme uses international standards including standards within the IEC 60079 series.

What is IEC 60079-29-1?

IEC 60079-29-1 specifies performance requirements for detectors used to detect flammable gases. It is one of the gas-detection standards recognised within the IECEx system.

What should engineers consider when selecting a portable gas detector?

Selection should consider the gases being monitored, expected concentration ranges, sensor technology, response time, sensitivity, battery life, operating environment, maintenance requirements and applicable hazardous-area certification requirements.