Comparing Single Gas and Multi Gas Detectors

Left unchecked, many of the gases produced in industry and research can present serious asphyxiation, poisoning, or explosion hazards. Gas detectors are the first line of defense against these invisible threats – but knowing which type of detector to use for a given application can be challenging. There’s a huge array of gas detection hardware on the market, from portable single-gas detectors to fixed sensor arrays capable of accurately monitoring large numbers of different gases simultaneously (known as multi-component or multi-gas detectors).

So, should you be using a single gas detector or a multi-gas detector?

The Importance of Gas Detection

Gas hazards can be broadly categorised as either asphyxiating (depriving the body of oxygen), toxic, or combustible. For petrochemical processing facilities, wastewater treatment plants, and a host of other industries, understanding the potential gas hazards in a given environment is an essential part of ensuring personnel safety.

Once specific gas hazards have been identified in a given environment and all possible measures taken to minimise the chances of dangerous accumulation or leaks of gas, vigilance must be maintained. Gas detectors, both fixed and portable, are essential life-saving devices that should be properly deployed in any environment where a gas hazard may be present.

Gas Detector Technology

Gas detection technology is highly diversified: there exists a huge range of different detectors, both specialised and generic, to suit virtually any conceivable application.¹

Devices generally fit one of two form factors: portable or fixed. Portable gas detectors are generally small enough to be worn on clothing or attached to a belt or lanyard. They can be carried around, providing constant monitoring of one or more target gases and alerting the user via audible alarm, vibration, and/or flashing lights when gas concentrations exceed a predefined level. Fixed gas monitors are installed in high-risk locations, and often provide higher accuracy, often including gas concentration measurement and data logging capabilities.

Single Gas vs Multi-Gas Detectors

Both portable and fixed detectors are available as either single gas or multi-gas detectors. Which of these to use is a question of application?

For most environments, where multiple gas hazards may be present, the decision to choose between single and multi-gas detectors requires careful consideration. Confined spaces must be tested for combustible gases, oxygen deficiency or enrichment, and the presence of two or three specific toxic gases. Many companies that primarily need to monitor a single gas choose to supplement this with monitoring of combustible gases, O² and CO.³ Measuring these three gases along with H²S is especially common in the oil and gas industry.

Multi-gas detectors are increasingly affordable and versatile: some portable gas detectors are capable of measuring as many as seven different gas components simultaneously.

Calibrating Multi-Gas Detectors

Of course, gas detectors alone cannot save lives if they’re not properly maintained and used. Virtually all gas detectors are prone to “drift”, a loss of accuracy due to environmental effects and age. All non-disposable gas detectors must be calibrated regularly to ensure that they are working properly. Multi-gas detectors contain multiple sensors for different gases, all of which must be calibrated: this can make calibration particularly time consuming. Fortunately, the time and effort required to calibrate a multi-gas sensor can be drastically reduced by using a multi-component calibration gas mixture. Using a multi-component reference gas mixture makes calibrating a four- or five-gas detector no more time consuming than a single gas detector.

If you have multi-gas detectors in need of calibration, Air Products can provide calibration gases for all common gas combinations. Our range of calibration gases are available in a range of canister sizes and concentrations – down to parts-per-billion levels. If you’re not sure what calibration gas mix to use for your multi-gas detector, get in touch with us today and we’ll be happy to advise you: 0800 389 0202, apukinfo@airproducts.com.

References and Further Reading

Xiong, L. & Compton, R. G. Amperometric Gas detection: A Review. Int. J. Electrochem. Sci 9, (2014).
Fixed or Portable Gas Detection? Available at: https://www.a1-cbiss.com/fixed-or-portable-gas-detection. (Accessed: 24th June 2020)
Four Gas Monitor — gas detection for complex environments. Available at: https://www.blacklinesafety.com/blog/four-gas-monitor-gas-detection. (Accessed: 24th June 2020)

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"Personal, portable and fixed gas detection equipment is widely used in many safety critical applications and these items are often subjected to relatively harsh environments and working conditions. The gas sensing element within this equipment is perhaps the most fragile and crucial component, and if this was to fail, it would render the equipment useless. The selection of appropriate test gas is important to ensure the bump test is carried out correctly and as an active member of CoGDEM, Air Products know about it. They have contributed to the CoGDEM Guide to Gas Detection, a new hardback reference book which explains best practice and aids the selection of suitable test gases and equipment."