A brief history of gas detection 

The evolution of gas detection has changed considerably over the years. New, innovative ideas from canaries to portable monitoring equipment provides workers with continuous precise gas monitoring. 

The Industrial Revolution was the catalyst in the development in gas detection due to the use of fuel that showed great promise, such as coal. As coal can be extracted from the earth through either mining or underground mining, tools like helmets and flame lights were their only protection from the dangers of methane exposure underground that were yet to be discovered. Methane gas is colourless and odourless, making it hard to know it’s presence until a noticeable pattern of health problems was discovered. The risks of gas exposure resulted in experimenting with detection methods to preserve the safety of the workers for years to come. 

A Need for Gas Detection 

Once gas exposure became apparent, miners understood that they needed to know whether the mine had any pocket of methane gas where they were working. In the early 19th century, the first gas detector was recorded with many miners wearing flame lights on their helmets to be able to see while they were working, so being able to detect the extremely flammable methane was paramount. The worker would wear a thick, wet blanket over their bodies while carrying a long wick with the end lit on fire. Entering the mines, the individual would move the flame around and along the walls looking for gas pockets. If found, a reaction would ignite and be noted to the crew while the person detecting was protected from the blanket. With time, more advanced methods of detecting gas were developed. 

The Introduction of Canaries 

Gas detection moved from humans to canaries due to their loud chirps and similar nervous systems for controlling breathing patterns. The canaries were placed in certain areas of the mine, from there, workers would check on the canaries to care for them as well as see if their health had been affected. During the work shifts, miners would listen to the canaries chirp. If a canaries began to shake its cage, that was a strong indicator of a gas pocket exposure in which it has started to affect its health. Miners would then evacuate the mine and noted that it was unsafe to enter. On some occasions if the canary stopped chirping all together, miners knew to make a swifter exit before the gas exposure had a chance to affect their health. 

The Flame Light 

The flame light was the next evolution for gas detection in the mine, as a result of worries about animal safety. Whilst providing light for the miners, the flame was housed in a flame-arrestor shell which absorbed any heat and captured the flame to prevent it from igniting any methane that may be present. The outside shell contained a glass piece with three incisions running horizontally. The middle line was set as the ideal gas environment while the bottom line indicated an oxygen-deficient environment, and the top line indicated methane exposure or an oxygen-enriched environment. Miners would light the flame in an environment with fresh air. If the flame lowered or started to die, it would indicate that the atmosphere had a low oxygen concentration. If the flame grew larger, the miners knew that methane was present with oxygen, both cases indicating that they needed to leave the mine. 

The Catalytic Sensor 

Although the flame light was a development in gas detection technology, it however, was not a ‘one size fits all’ approach for all industries. Therefore, the catalytic sensor was the first gas detector that has a resemblance to modern technology. The sensors work on the principle that when a gas oxidises, it produces heat. The catalytic sensor works through temperature change, which is proportional to the concentration of gas. Whilst this was a step forward in the development of the technology required for gas detection, it still initially required manual operation in order to receive a reading. 

Modern Day Technology 

Gas detection technology has been developed tremendously since the early 19th century in which the first gas detector was recorded. With now over five different types of sensors commonly used across all industries, including Electrochemical, Catalytic Beads (Pellistor), Photoionisation detector (PID) and Infrared Technology (IR), along with the most modern sensors Molecular Property Spectrometer™ (MPS) and Long-Life Oxygen (LLO2), modern day gas detectors are highly sensitive, accurate but most importantly reliable, all of which allow for all personnel to stay safe reducing the number of workplace fatalities. 

The Benefits of MPS Sensors 

Developed by NevadaNano, Molecular Property Spectrometer™ (MPS™) sensors represent the new generation of flammable gas detectors. MPS™ can quickly detect over 15 characterised flammable gases at once. Until recently, anyone who needed to monitor flammable gases had to select either a traditional flammable gas detector containing a pellistor sensor calibrated for a specific gas, or containing an infra-red (IR) sensor which also varies in output according to the flammable gas being measured, and hence needs to be calibrated for each gas. While these remain beneficial solutions, they are not always ideal. For example, both sensor types require regular calibration and the catalytic pellistor sensors also need frequent bump testing to ensure they have not been damaged by contaminants (known as ‘sensor poisoning’ agents) or by harsh conditions. In some environments, sensors must frequently be changed, which is costly in terms of both money and downtime, or product availability. IR technology cannot detect hydrogen – which has no IR signature, and both IR and pellistor detectors sometimes incidentally detect other (i.e., non-calibrated) gases, giving inaccurate readings that may trigger false alarms or concern operators. 

The MPS™ sensor delivers key features that provide real world tangible benefits to operator and hence workers. These include: 

No calibration  

When implementing a system containing a fixed head detector, it is common practice to service on a recommended schedule defined by manufacturer. This entails ongoing regular costs as well potentially disrupting production or process in order service or even gain access to detector or multiple detectors. There may also be a risk to personnel when detectors are mounted in particularly hazardous environments. Interaction with an MPS sensor is less stringent because there are no unrevealed failure modes, provided air is present. It would be wrong to say there is no calibration requirement. One factory calibration, followed by a gas test when commissioning is sufficient, because there is an internal automated calibration being performed every 2 seconds throughout the working life of the sensor. What is really meant is – no customer calibration. 

The Xgard Bright with MPS™ sensor technology does not require calibration. This in turn reduces the interaction with the detector resulting in a lower total cost of ownership over the sensor life cycle and reduced risk to personnel and production output to complete regular maintenance. It is still advisable to check the cleanliness of the gas detector from time to time, since gas can’t get through thick build ups of obstructive material and wouldn’t then reach the sensor. 

Multi species gas – ‘True LEL’™  

Many industries and applications use or have as a by-product multiple gases within the same environment. This can be challenging for traditional sensor technology which can detect only a single gas that they were calibrated for at the correct level and can result in inaccurate reading and even false alarms which can halt process or production if another flammable gas type is present. The lack of response or over response frequently faced in multi gas environments can be frustrating and counterproductive compromising safety of best user practices. The MPS™ sensor can accurately detect multiple gases at once and instantly identify gas type. Additionally, the MPS™ sensor has a on board environmental compensation and does not require an externally applied correctional factor. Inaccurate readings and false alarms are a thing of the past.  

No sensor poisoning  

In certain environments traditional sensor types can be under risk of poisoning. Extreme pressure, temperature, and humidity all have the potential to damage sensors whist environmental toxins and contaminants can ‘poison’ sensors, leading to severely compromised performance. Detectors in environments where poisons or inhibitors may be encountered, regular and frequent testing is the only way to ensure that performance is not being degraded. Sensor failure due to poisoning can be a costly experience. The technology in the MPS™ sensor is not affected by contaminates in the environment. Processes that have contaminates now have access to a solution that operates reliably with fail safe design to alert operator to offer a peace of mind for personnel and assets located in hazardous environment. Additionally, the MPS sensor is not harmed by elevated flammable gas concentrations, which may cause cracking in conventional catalytic sensor types for example. The MPS sensor carries on working. 

Hydrogen (H2)

The usage of Hydrogen in industrial processes is increasing as the focus to find a cleaner alternative to natural gas usage. Detection of Hydrogen is currently restricted to pellistor, metal oxide semiconductor, electrochemical and less accurate thermal conductivity sensor technology due to Infra-Red sensors inability to detect Hydrogen. When faced with challenges highlighted above in poisoning or false alarms, the current solution can leave operator with frequent bump testing and servicing in addition to false alarm challenges. The MPS™ sensor provides a far better solution for Hydrogen detection, removing the challenges faced with traditional sensor technology. A long-life, relatively fast responding hydrogen sensor that does not require calibration throughout the life cycle of the sensor, without the risk of poisoning or false alarms, can significantly save on total cost of ownership and reduces interaction with unit resulting in peace of mind and reduced risk for operators leveraging MPS™ technology. All of this is possible thanks to MPS™ technology, which is the biggest breakthrough in gas detection for several decades. The Gasman with MPS is hydrogen (H2) ready. A single MPS sensor accurately detects hydrogen and common hydrocarbons in a fail-safe, poison-resistant solution without recalibration.

For more on Crowcon, visit https://www.crowcon.com or for more on MPSTM visit https://www.crowcon.com/mpsinfixed/  

How Long will my Gas Sensor Last?

Gas detectors are used extensively within many industries (such as water treatment, refinery, petrochemical, steel and construction to name a few) to protect personnel and equipment from dangerous gases and their effects. Users of portable and fixed devices will be familiar with the potentially significant costs of keeping their instruments operating safely over their operational life. Gas sensors are understood to provide a measurement of the concentration of some analyte of interest, such as CO (carbon monoxide), CO2 (carbon dioxide), or NOx (nitrogen oxide). There are two most used gas sensors within industrial applications: electrochemical for toxic gases and oxygen measurement, and pellistors (or catalytic beads) for flammable gases. In recent years, the introduction of both Oxygen and MPS (Molecular Property Spectrometer) sensors have allowed for improved safety.  

How do I know when my sensor has failed? 

There have been several patents and techniques applied to gas detectors over the past few decades which claim to be able to determine when an electrochemical sensor has failed. Most of these however, only infer that the sensor is operating through some form of electrode stimulation and might provide a false sense of security. The only sure method of demonstrating that a sensor is working is to apply test gas and measure the response: a bump test or full calibration. 

Electrochemical Sensor  

Electrochemical sensors are the most used in diffusion mode in which gas in the ambient environment enters through a hole in the face of the cell. Some instruments use a pump to supply air or gas samples to the sensor. A PTFE membrane is fitted over the hole to prevent water or oils from entering the cell. Sensor ranges and sensitivities can be varied in design by using different size holes. Larger holes provide higher sensitivity and resolution, whereas smaller holes reduce sensitivity and resolution but increase the range. 

Factors affecting Electrochemical Sensor Life 

There are three main factors that affect the sensor life including temperature, exposure to extremely high gas concentrations and humidity. Other factors include sensor electrodes and extreme vibration and mechanical shocks.  

Temperature extremes can affect sensor life. The manufacturer will state an operating temperature range for the instrument: typically -30˚C to +50˚C. High quality sensors will, however, be able to withstand temporary excursions beyond these limits. Short (1-2 hours) exposure to 60-65˚C for H2S or CO sensors (for example) is acceptable, but repeated incidents will result in evaporation of the electrolyte and shifts in the baseline (zero) reading and slower response. 

Exposure to extremely high gas concentrations can also compromise sensor performance. Electrochemical sensors are typically tested by exposure to as much as ten-times their design limit. Sensors constructed using high quality catalyst material should be able to withstand such exposures without changes to chemistry or long-term performance loss. Sensors with lower catalyst loading may suffer damage.  

The most considerable influence on sensor life is humidity. The ideal environmental condition for electrochemical sensors is 20˚Celsius and 60% RH (relative humidity). When the ambient humidity increases beyond 60%RH water will be absorbed into the electrolyte causing dilution. In extreme cases the liquid content can increase by 2-3 times, potentially resulting in leakage from the sensor body, and then through the pins. Below 60%RH water in the electrolyte will begin to de-hydrate. The response time may be significantly extended as the electrolyte or dehydrated. Sensor electrodes can in unusual conditions be poisoned by interfering gases that adsorb onto the catalyst or react with it creating by-products which inhibit the catalyst.  

Extreme vibration and mechanical shocks can also harm sensors by fracturing the welds that bond the platinum electrodes, connecting strips (or wires in some sensors) and pins together.  

‘Normal’ Life Expectancy of Electrochemical Sensor 

Electrochemical sensors for common gases such as carbon monoxide or hydrogen sulphide have an operational life typically stated at 2-3 years. More exotic gas sensor such as hydrogen fluoride may have a life of only 12-18 months. In ideal conditions (stable temperature and humidity in the region of 20˚C and 60%RH) with no incidence of contaminants, electrochemical sensors have been known to operate more than 4000 days (11 years). Periodic exposure to the target gas does not limit the life of these tiny fuel cells: high quality sensors have a large amount of catalyst material and robust conductors which do not become depleted by the reaction. 

Pellistor Sensor 

Pellistor sensors consist of two matched wire coils, each embedded in a ceramic bead. Current is passed through the coils, heating the beads to approximately 500˚C. Flammable gas burns on the bead and the additional heat generated produces an increase in coil resistance which is measured by the instrument to indicate gas concentration. 

Factors affecting Pellistor Sensor Life 

The two main factors that affect the sensor life include exposure to high gas concentration and poising or inhibition of the sensor. Extreme mechanical shock or vibration can also affect the sensor life. The capacity of the catalyst surface to oxidise the gas reduces when it has been poisoned or inhibited. Sensor life more than ten years is common in applications where inhibiting or poisoning compounds are not present. Higher power pellistors have greater catalytic activity and are less vulnerable to poisoning. More porous beads also have greater catalytic activity as their surface volume in increased. Skilled initial design and sophisticated manufacturing processes ensure maximum bead porosity. Exposure to high gas concentrations (>100%LEL) may also compromise sensor performance and create an offset in the zero/base-line signal. Incomplete combustion results in carbon deposits on the bead: the carbon ‘grows’ in the pores and creates mechanical damage. The carbon may however be burned off over time to re-reveal catalytic sites. Extreme mechanical shock or vibration can in rare cases also cause a break in the pellistor coils. This issue is more prevalent on portable rather than fixed-point gas detectors as they are more likely to be dropped, and the pellistors used are lower power (to maximise battery life) and thus use more delicate thinner wire coils. 

How do I know when my sensor has failed? 

A pellistor that has been poisoned remains electrically operational but may fail to respond to gas. Hence the gas detector and control system may appear to be in a healthy state, but a flammable gas leak may not be detected. 

Oxygen Sensor 

Long Life 02 Icon

Our new lead-free, long-lasting oxygen sensor does not have compressed strands of lead the electrolyte has to penetrate, allowing a thick electrolyte to be used which means no leaks, no leak induced corrosion, and improved safety. The additional robustness of this sensor allows us to confidently offer a 5-year warranty for added piece of mind. 

Long life-oxygen sensors have an extensive lifespan of 5-years, with less downtime, lower cost of ownership, and reduced environmental impact. They accurately measure oxygen over a broad range of concentrations from 0 to 30% volume and are the next generation of O2 gas detection. 

MPS Sensor  

MPS sensor provides advanced technology that removes the need to calibrate and provides a ‘True LEL (lower explosive limit)’ for reading for fifteen flammable gases but can detect all flammable gases in a multi-species environment, resulting in lower ongoing maintenance costs and reduced interaction with the unit. This reduces risk to personnel and avoids costly downtime. The MPS sensor is also immune to sensor poisoning.  

Sensor failure due to poisoning can be a frustrating and costly experience. The technology in the MPS™ sensor is not affected by contaminates in the environment. Processes that have contaminates now have access to a solution that operates reliably with fail safe design to alert operator to offer a peace of mind for personnel and assets located in hazardous environment. It is now possible to detect multiple flammable gases, even in harsh environments, using just one sensor that does not require calibration and has an expected lifespan of at least 5 years.