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Gas Detection

There is a Massive amount of Technical Engineering Information for Instrument and Fire & Gas Engineers on this page - so make life easy and Go the Subject Area that you are interested in:- Principles of Gas Detection | Gas Detection Technical ReferencesComparision of Gas Detection Technologies | Maintenance of Gas Detection Systems | Planning and Designing Gas Detection Systems | Addressable Gas Detectors | Air Duct Gas Detection | Catalytic Combustible Gas Detectors | Calibrating Gas Sensors | Calibration Gas for Gas Detectors | Open Path Infra Red Gas Detectors | Gas Detection Certification | Gas Detection using Laser Technology | Gas Detection using Photoacoustic Infrared Technology | Gas Detection in Gas Turbines and Compressor Stations | Gas Detection Standards | Portable Gas Detection | Portable Gas Detection Bump Testing | Photoionization Detectors | Toxic Gas Monitors | Ultrasonic Gas Leak Detection

Principles of Gas Detection

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Combustible Gas Sensors    
Many people have probably seen a flame safety lamp at some time and know something about its use as an early form of ‘firedamp’ gas detector in underground coal mines and sewers. 

Although originally intended as a source of light, the device could also be used to estimate the level of combustible gases- to an accuracy of about 25-50%, depending on the user’s experience, training, age, colour perception etc. Modern combustible gas detectors have to be much more accurate, reliable and repeatable than this and although various attempts were made to overcome the safety lamp’s subjectiveness of measurement (by using a flame temperature sensor for instance), it has now been almost entirely superseded by more modern, electronic devices. 

Nevertheless, today’s most commonly used device, the catalytic detector, is in some respects a modern development of the early flame safety lamp, since it also relies for its operation on the combustion of a gas and its conversion to Carbon Dioxide and water.

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Catalytic Sensor
Nearly all modern, low-cost, combustible gas detection sensors are of the electro-catalytic type. They consist of a very small sensing element sometimes called a ‘bead’, a ‘Pellistor’, or a ‘Siegistor’- the last two being registered trade names for commercial devices. They are made of an electrically heated platinum wire coil, covered first with a ceramic base such as Alumina and then with a final outer coating of Palladium or Rhodium catalyst dispersed in a substrate of Thoria. 

This type of sensor operates on the principle that when a combustible gas/air mixture passes over the hot catalyst surface, combustion occurs and the heat evolved increases the temperature of the ‘bead’. This in turn alters the resistance of the platinum coil and can be measured by using the coil as a temperature thermometer in a standard electrical bridge circuit. The resistance change is then directly related to the gas concentration in the surrounding atmosphere and can be displayed on a meter or some similar indicating device.

Sensor Output
To ensure temperature stability under varying ambient conditions, the best catalytic sensors use thermally matched beads. They are located in opposing arms of a Wheatstone bridge electrical circuit, where the ‘sensitive’ sensor (usually known as the ‘s’ sensor) will react to any combustible gases present, whilst a balancing, ‘inactive’ or ‘non-sensitive’ (n-s) sensor will not. Inactive operation is achieved by either coating the bead with a film of glass or de-activating the catalyst so that it will act only as a compensator for any external temperature or humidity changes.

A further improvement in stable operation can be achieved by the use of poison resistant sensors. These have better resistance to degradation by substances such as Silicones, Sulphur and Lead compounds which can rapidly de-activate (or ‘poison’) other types of catalytic sensor.

Speed of Response

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To achieve the necessary requirements of design safety, the catalytic type of sensor has to be mounted in a strong metal housing behind a flame arrestor. This allows the gas/air mixture to diffuse into the housing and on to the hot sensor element, but will prevent the propagation of any flame to the outside atmosphere. The flame arrestor slightly reduces the speed of response of the sensor but, in most cases the electrical output will give a reading in a matter of seconds after gas has been detected. However, because the response curve is considerably flattened as it approaches the final reading, the response time is often specified in terms of the time to reach 90 percent of its final reading and is therefore known as the T90 value. T90 values for catalytic sensors are typically between 20 and 30 seconds. 

(N.B. In the USA and some other countries, this value is often quoted as the lower T60 reading and care should therefore be taken when comparing the performance of different sensors).

Calibration

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The most common failure in catalytic sensors is performance degradation caused by exposure to certain poisons’. It is therefore essential that any gas monitoring system should not only be calibrated at the time of installation, but also checked regularly and re-calibrated as necessary. Checks must be made using an accurately calibrated standard gas mixture so that the zero and ‘span’ levels can be set correctly on the controller.

Codes of practice such as EN50073:1999 can provide some guidance about the calibration checking frequency and the alarm level settings. Typically, checks should initially be made at weekly intervals but the periods can be extended as operational experience is gained. Where two alarm levels are required, these are normally set at 20-25% LEL for the lower level and 50-55% LEL for the upper level. 

Older (and lower cost) systems require two people to check and calibrate, one to expose the sensor to a flow of gas and the other to check the reading shown on the scale of its control unit. Adjustments are then made at the controller to the zero and span potentiometers until the reading exactly matches that of the gas mixture concentration. 

Remember that where adjustments have to be made within a flameproof enclosure, the power must first be disconnected and a permit obtained to open the enclosure.

Today, there are a number of ‘one-man’ calibration systems available which allow the calibration procedures to be carried out at the sensor itself. This considerably reduces the time and cost of maintenance, particularly where the sensors are in difficult to get to locations, such as an offshore oil or gas platform. Alternatively, there are now some sensors available which are designed to intrinsically safe standards, and with these it is possible to calibrate the sensors at a convenient place away from the site (in a maintenance depot for instance). Because they are intrinsically safe, it is allowed to freely exchange them with the sensors needing replacement on site, without first shutting down the system for safety. 

Maintenance can therefore be carried out on a ‘hot’ system and is very much faster and cheaper than early, conventional systems.  

Semiconductor Sensor

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Sensors made from semiconducting materials gained considerably in popularity during the late 1980s and at one time appeared to offer the possibility of a universal, low cost gas detector. In the same way as catalytic sensors, they operate by virtue of gas absorption at the surface of a heated oxide. In fact, this is a thin metal-oxide film (usually oxides of the transition metals or heavy metals, such as tin) deposited on a silicon slice by much the same process as is used in the manufacture of computer ‘chips’. Absorption of the sample gas on the oxide surface, followed by catalytic oxidation, results in a change of electrical resistance of the oxide material and can be related to the sample gas concentration. The surface of the sensor is heated to a constant temperature of about 200-250°C, to speed up the rate of reaction and to reduce the effects of ambient temperature changes.

Semiconductor sensors are simple, fairly robust and can be highly sensitive. They have been used with some success in the detection of Hydrogen Sulphide gas, and they are also widely used in the manufacture of inexpensive domestic gas detectors. However, they have been found to be rather unreliable for industrial applications, since they are not very specific to a particular gas and they can be affected by atmospheric temperature and humidity variations. They probably need to be checked more often than other types of sensor, because they have been known to ‘go to sleep’ (i.e. lose sensitivity) unless regularly checked with a gas mixture and they are slow to respond and recover after exposure to an outburst of gas. 

Thermal Conductivity

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This technique for detecting gas is suitable for the measurement of high (%V/V) concentrations of binary gas mixes. It is mainly used for detecting gases with a thermal conductivity much greater than air e.g. Methane and Hydrogen. Gases with thermal conductivities close to air cannot be detected E.g. Ammonia and Carbon Monoxide. Gases with thermal conductivities less than air are more difficult to detect as water vapour can cause interference E.g. Carbon Dioxide and Butane. Mixtures of two gases in the absence of air can also be measured using this technique.

The heated sensing element is exposed to the sample and the reference element is enclosed in a sealed compartment. If the thermal conductivity of the sample gas is higher than that of the reference, then the temperature of the sensing element decreases. If the thermal conductivity of the sample gas is less than that of the reference then the temperature of the sample element increases. These temperature changes are proportional to the concentration of gas present at the sample element. 

Infrared Gas Detector
Many combustible gases have absorption bands in the infrared region of the electromagnetic spectrum of light and the principle of infrared absorption has been used as a laboratory analytical tool for many years. Since the 1980s, however, electronic and optical advances have made it possible to design equipment of sufficiently low power and smaller size to make this technique available for industrial gas detection products as well.

These sensors have a number of important advantages over the catalytic type. They include a very fast speed of response (typically less than 10 seconds), low maintenance and greatly simplified checking, using the self-checking facility of modern micro-processor controlled equipment. They can also be designed to be unaffected by any known ‘poisons’, they are failsafe and they will operate successfully in inert atmospheres, and under a wide range of ambient temperature, pressure and humidity conditions. 

The technique operates on the principle of dual wavelength IR absorption, whereby light passes through the sample mixture at two wavelengths, one of which is set at the absorption peak of the gas to be detected, whilst the other is not. The two light sources are pulsed alternatively and guided along a common optical path to emerge via a flameproof ‘window’ and then through the sample gas. The beams are subsequently reflected back again by a retro-reflector, returning once more through the sample and into the unit. Here a detector compares the signal strengths of sample and reference beams and, by subtraction, can give a measure of the gas concentration. 

This type of detector can only detect diatomic gas molecules and is therefore unsuitable for the detection of Hydrogen.

Open Path Flammable Infrared Gas Detector
Traditionally, the conventional method of detecting gas leaks was by point detection, using a number of individual sensors to cover an area or perimeter. More recently, however, instruments have become available which make use of infrared and laser technology in the form of a broad beam (or open path) which can cover a distance of several hundred metres. Early open path designs were typically used to complement point detection, however the latest 3rd generation instruments are now often being used as the primary method of detection. Typical applications where they have had considerable success include FPSOs, add jettys, loading/unloading terminals, pipelines, perimeter monitoring, off-shore platforms and LNG (Liquid Natural Gas) storage areas.

Early designs use dual wavelength beams, the first coinciding with the absorption band peak of the target gas and a second reference beam which lies nearby in an unabsorbed area. The instrument continually compares the two signals that are transmitted through the atmosphere, using either the back-scattered radiation from a retroreflector or more commonly in newer designs by means of a separate transmitter and receiver. Any changes in the ratio of the two signals is measured as gas. However, this design is susceptible to interference from fog as different types of fog can positively or negatively affect the ratio of the signals and thereby falsely indicate an upscale gas reading/alarm or downscale gas reading/fault. The latest 3rd generation design uses a double band pass filter that has two reference wavelengths (one either side of the sample) that fully compensates for interference from all types of fog and rain. Other problems associated with older designs have been overcome by the use of coaxial optical design to eliminate false alarms caused by partial obscuration of the beam and the use of xenon flash lamps and solid state detectors making the instruments totally immune to interference from sunlight or other sources of radiation such as flare stacks, arc welding or lightning.

Open path detectors actually measure the total number of gas molecules (i.e. the quantity of gas) within the beam. This value is different to the usual concentration of gas given at a single point and is therefore expressed in terms of LEL meters.

Electrochemical Sensor
Gas specific electrochemical sensors can be used to detect the majority of common toxic gases, including CO, H2S, Cl2, SO2 etc. in a wide variety of safety applications. 

Electrochemical sensors are compact, require very little power, exhibit excellent linearity and repeatability and generally have a long life span, typically one to three years. Response times, denoted as T90, i.e. time to reach 90% of the final response, are typically 30-60 seconds and minimum detection limits range from 0.02 to 50ppm depending upon target gas type. 

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Commercial designs of electrochemical cell are numerous but share many of the common features described below: 

Three active gas diffusion electrodes are immersed in a common electrolyte, frequently a concentrated aqueous acid or salt solution, for efficient conduction of ions between the working and counter electrodes.

Depending on the specific cell the target gas is either oxidised or reduced at the surface of the working electrode. This reaction alters the potential of the working electrode relative to the reference electrode. The primary function of the associated electronic driver circuit connected to the cell is to minimise this potential difference by passing current between the working and counter electrodes, the measured current being proportional to the target gas concentration. Gas enters the cell through an external diffusion barrier that is porous to gas but impermeable to liquid.  

Many designs incorporate a capillary diffusion barrier to limit the amount of gas contacting the working electrode and thereby maintaining “amperometric” cell operation. 

A minimum concentration of Oxygen is required for correct operation of all electrochemical cells, making them unsuitable for certain process monitoring applications. Although the electrolyte contains a certain amount of dissolved Oxygen, enabling short-term detection (minutes) of the target gas in an Oxygen-free environment, it is strongly advised that all calibration gas streams incorporate air as the major component or diluent. 

Specificity to the target gas is achieved either by optimisation of the electrochemistry, i.e. choice of catalyst and electrolyte, or else by incorporating filters within the cell which physically absorb or chemically react with certain interferent gas molecules in order to increase target gas specificity. It is important that the appropriate product manual be consulted to understand the effects of potential interferent gases on the cell response.

The necessary inclusion of aqueous electrolytes within electrochemical cells results in a product that is sensitive to environmental conditions of both temperature and humidity. To address this, the patented Surecell™ design incorporates two electrolyte reservoirs that allows for the ‘take up’ and ‘loss’ of electrolyte that occurs in high temperature/high humidity and low temperature/low humidity environments.  

Electrochemical sensor life is typically warranted for 2 years, but the actual lifetime frequently exceeds the quoted values. The exceptions to this are Oxygen, Ammonia and Hydrogen Cyanide sensors where components of the cell are necessarily consumed as part of the sensing reaction mechanism. 

Chemcassette®
Chemcassette® is based on the use of an absorbent strip of filter paper acting as a dry reaction substrate. This performs both as a gas collecting and gas analysing media and it can be used in a continuously operating mode. The system is based on classic colorimetry techniques and is capable of extremely low detection limits for a specific gas. It can be used very successfully for a wide variety of highly toxic substances, including Di-isocyanates, Phosgene, Chlorine, Fluorine and a number of the hydride gases employed in the manufacture of semiconductors. 

Detection specificity and sensitivity are achieved through the use of specially formulated chemical reagents, which react only with the sample gas or gases. As sample gas molecules are drawn through the Chemcassette® with a vacuum pump, they react with the dry chemical reagents and form a coloured stain specific to that gas only. The intensity of this stain is proportionate to the concentration of the reactant gas, ie, the higher the gas concentration, the darker is the stain. By carefully regulating both the sampling interval and the flow rate at which the sample is presented to the Chemcassette®, detection levels as low as parts-per-billion (ie, 10 -9) can be readily achieved. 

Stain intensity is measured with an electro-optical system which reflects light from the surface of the substrate to a photo cell located at an angle to the light source. Then, as a stain develops, this reflected light is attenuated and the reduction of intensity is sensed by the photo detector in the form of an analogue signal. This signal is, in turn, converted to a digital format and then presented as a gas concentration, using an internally-generated calibration curve and an appropriate software library. Chemcassette® formulations provide a unique detection medium that is not only fast, sensitive and specific, but it is also the only available system which leaves physical evidence (i.e. the stain on the cassette tape) that a gas leak or release has occurred.

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Comparison of Gas Detection Techniques

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The following Gas Detector references are from sources which provide what ICEweb considers to be the best technical and educational information on the subject. We always acknowledge the author and source. Should there be any issue with ICEweb providing this information, please contact us and we will remove it immediately. We also welcome non-commercial technical documents (subject to editorial review) and post them free - ICEweb is a Free Technical Information Website for Instrument, Control, Fire & Gas and SIS Engineers and page sponsorships provide the funding to cover running costs. For further details contact us here.

Gas Detection Technical Design Engineering References for Instrument and Fire & Gas Engineers 

Honeywell Analytics Gas Book - This comprehensive handbook is intended to offer a simple guide to anyone considering the use of gas detection equipment. It provides an explanation of both the principles involved and the instrumentation needed for satisfactory protection of personnel, plant and environment. The aim has been to answer as many as possible of the most commonly asked questions about the selection and use of industrial gas detection equipment. Be patient, this document may take a while to download. 
At The Heart of Gas Detection Systems - Detecting Hazards - Quite Simple in Principle- Why It Is Worth Knowing More About Gas Detection Sensors - Our sensory organs are often unable to detect airborne hazards, or cannot do so early enough. Toxic or flammable gases and vapours can build up, reaching hazardous concentrations, or there may be insufficient oxygen in the air. Both of these scenarios can have life-threatening consequences. The reliability with which harmful airborne substances can be detected depends to a large extent on the sensors that are used. It is essential for the gas detector and sensor to be adapted perfectly to each other. Hazards must be identified in good time and dependably, and false alarms leading to production downtime and the like must be avoided. You entrust the safety and protection of your personnel, equipment and property to a perfectly working sensor - from Draeger.
Explosion Hazards Mostly Arise from Flammable Gases And Vapours - Instead of avoiding their ignition by explosion protection measures it maybe preferable to detect them before they become ignitable. Depending on the application different measuring principles for the detection of gases and vapours can be used: Catalytic bead sensors, point or open-path infrared sensors - from Draeger. This Covers:
- Preventing potentially explosive atmospheres – primary explosion protection
- Safety relevant data of flammable gases and vapours
- Avoiding effective ignition sources – secondary explosion protection
- Utilisation of gas detection systems reducing the probability of formation of explosive atmospheres
- Pellistor sensors and Infrared sensors
- Proper calibration and sensor positioning of a gas detection system
Gas Detection Handbook - This Gas Detection Handbook from MSA is designed to introduce users to key terms and concepts in gas detection and to serve as a quick reference manual for information such as specific gas properties, exposure limits and other data. The Handbook contains;
- A glossary of essential gas detection terms and abbreviations.
- A summary of key principles in combustible and toxic gas monitoring.
- Reference data—including physical properties and exposure limits for the most commonly monitored gases, in industrial and various other environments.
- A comparison of the most widely-used gas detection technologies.
- A table indicating the gas hazards common to specific applications within major industries.
- A summary of key gas detection instrumentation approvals information, including hazardous locations classification.
- A Sensor Placement Guide, detailing important factors to take into consideration when determining optimum gas sensor placement.
Gas Detection for Offshore Application - Peter Okoh - This is an excellent paper - Release of hazardous and flammable gas is a significant contributor to risk in the offshore oil and gas industry and various types of automatic systems for rapid detection of gas are therefore installed to accentuate the elimination or reduction of the dangerous releases. There are different types of gases which may be released and gas may be released in different environments and under different conditions. Several principles for detecting gas are therefore applied and a variety of types of gas detectors are in use. However, a significant percentage of gas releases remain undetected by the dedicated detectors and hence unaccounted for and uncontrolled. The objectives of this paper are: (1) to present a state-of-the art overview of gas detection in relation to offshore applications, (2) to present an overview of requirements for gas detection in the Norwegian off- shore industry, and (3) to do a comparative study of performance standards for gas detection worldwide. The paper builds on a review of literature, standards and guidelines in relation to gas detection offshore - from Probabilistic Safety Assessment and Management.
Positioning of Gas Detectors at Offshore Installations - Julian André Båfjord - This excellent thesis studies different factors which must be considered when selecting the best suited positions for gas detectors at offshore installations where production of oil and gas takes place and evaluate their degree of impact on the functionality and reliability of the gas detection system. The different factors’ influence on the risk level related to undesired gas releases are discussed as well - from BIBSYS Brage .
Introduction to Gas Detection - The detection of hazardous gases has always been a complex subject and makes choosing an appropriate gas monitoring instrument a difficult task. This excellent introductory chapter from International Sensor Technology covers;
- Analytical Instruments and Monitoring Systems
- Gas Sensors
- Terms, Definitions, and Abbreviations
- Units of Measure for Gas Concentration
- Equations for Deriving Units of Gas Concentration
- Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL)
- Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL)
- Toxic Gases
- Performance Specifications
- Hazardous Locations
- Types of Protection
- Enclosure Classifications For Nonhazardous Areas
Sensor Selection Guide  - Electrochemical, Catalytic Bead, Solid State, Infrared and Photoionization Detectors must meet certain criteria to be practical for use in area air quality and safety applications. Some of the basic requirements are detailed in this chapter from International Sensor Technology which also includes a useful look up table. Also detailed are Factors to Consider When Selecting Sensors and Toxic versus Combustible Gas Monitoring,
Gas Detection Technology and Applications- This is a 52 page booklet full of good F&G information.
Fundamentals of Combustible Gas Detection - A 36 page technical Guide on the Characteristics of Combustible Gases and Applicable Detection Technologies  - from General Monitors
Why is Hydrogen Leak Detection Important? - Hydrogen is one of the three most dangerous combustible gases; the other two are Acetylene and Carbon Disulphide. These gases are particularly dangerous as they need very small ignition energy to ignite them (the minimum ignition energy of Hydrogen is just 40uJ) and for this reason have a separate gas group IIC as per the European standard - from Honeywell Analytics.
Gas Leak Detection for Boiler Rooms in Commercial and Industrial Property - Natural gas is one of the most widely used fuels for heating commercial and industrial property. In the event of an undetected leak it can present an explosive risk leading to structural damage, the loss of life or an expensive waste of fuel. Most boiler plant rooms are visited infrequently and therefore any leak will go undetected. An automatic gas detection system will provide early warning of a gas release during unmanned periods - from Honeywell Analytics.
List of Detectable Gases and Vapours - This list whilst being associated with Drager Equipment provides comprehensive information on gases and Vapours, Composition, LEL etc.
Infrared (IR) Gas Detection Technology is Keeping Field Personnel Safer - LED-Driven Infrared Sensors: Shining New Light on LEL Gas Measurement for Oil and Gas and Confined Space Entry Applications - Oil and gas production and work in confined spaces exposes field personnel to a variety of toxic and explosive gases in every day drilling, processing, transport and municipal operations. Explosive gas build-ups can endanger not only the workers nearby, but also a widespread area beyond the working area, making fast, accurate measurement of combustible gases below LEL levels critical to maintaining safety. Today, there are two main sensor technologies used for detecting explosive gases: catalytic bead and infrared - from Gas Clip Technologies.
Monitoring Flammable Vapours and Gases - This paper gives a different approach whilst still covering the more conventional techniques - from Control Instruments Corporation
Measuring Solvent, Fuel and Volatile Organic Compounds (VOC) Vapours in the Workplace Environment - Robert E. Henderson - Solvent, fuel and many other VOC vapours are pervasively common in many workplace environments. Most have surprisingly low occupational exposure limits. For most VOCs, long before you reach a concentration sufficient to register on a combustible gas indicator, you will have easily exceeded the toxic exposure limits for the contaminant - from BW Technologies.  

The following paper is from ICEweb sponsor IDC Technologies - Specialists In Engineering Courses & Training
Introduction to Functional Safety Standards in Gas Detection - Preeju Anirudhan - Draeger Safety Pacific Pty Ltd - The objective of this session is to create awareness on gas detection and the various technologies used in gas detection, including the role of gas detectors in risk reduction. This paper covers gas dispersion & placement of sensors and the considerations that must be given while deciding sensor technology, sensor placement and maintenance of the detectors, with a life-cycle approach. It also discusses the various standards applicable in the field of gas detection, functional safety applications, including standards applicable to plants & projects. In addition it addresses common mistakes due to incorrect use of standards, controller and precautions that must be taken while using PLC’s and the limitations of using PLC’s for gas detection applications - from the IDC Safety Control Systems Conference 2015

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Comparison of Gas Detection Technologies

It is important to compare Gas Detection technologies because there are different advantages and disadvantages to each technology and application. For instance Infrared will not work when one requires to measure Hydrogen. Catalytic Detectors may be "poisoned" and also are very maintenance prone. Thus all Instrument and Fire & Gas Engineers must be aware of the differences and be able to make a correct decision as to which one to utilise.

The following references are very useful.

Combustible Gas Detector Sensor Drift: Catalytic vs Infrared - Kelly Rollick, Allan Roczko, and Leslie Mitchell - Catalytic bead combustible sensor technology, used for decades to measure combustible gas concentrations, dates back to the 1830s. The infrared spectrum was discovered in 1800. The 1950s saw a surge in infrared spectrum use for many technological applications, including gas detection. These distinct gas detection technologies offer advantages and disadvantages, with conditions determining the better choice for specific applications - from ISA
Detecting Combustible Gases and Vapours - Catalytic Bead or Infrared? -Anyone wishing to detect combustible gases and vapours is generally faced with the following important questions: Is it better to use the more economical catalytic bead sensors or the longer life infrared sensors? What are the advantages and disadvantages of each? What points are important to note? Are there certain applications which are better suited to one or the other method? This article aims to provide answers to the questions most frequently asked in this context - from Draeger Australia.
Comparison of Gas Detection Technologies – Covers Electrochemical Sensors, Metal Oxide Semiconductor (MOS) Sensors, Photoacoustic Sensors and Infrared Sensors - from OI Analytical.
Combustible Gas Safety Monitoring: Infrared vs. Catalytic Gas Detectors - A booklet which advises when to use the various technologies - from General Monitors.


Maintenance of Gas Detection Systems

Ask the Gas Detection Experts - Although certain principles of gas detection require less maintenance than others, the calibration and servicing frequency of gas detection equipment is largely dependent on the environment and application where it is being used. Weather conditions, dust, dirt, water and even the types of compounds being used nearby can have an effect on the performance of equipment and influence the frequency of maintenance activities.
Placement & Maintenance of Fixed-Point Gas Monitoring Systems - Matt Thiel - Gas detectors are typically exposed to some of the harshest conditions. They are placed in areas where they are exposed to extreme weather, dust, dirt, oil, and debris. These products are designed to operate in these conditions, but the instruments should be inspected on a regular basis - from Industrial Scientific Corporation.
Maintaining Catalytic Combustible Gas Detectors - In oil / gas and petrochemical production, refining, transportation and distribution facilities, safety is always of paramount concern due to the combustible nature of hydrocarbon-based products. All such facilities must install combustible gas monitoring systems to protect people and equipment. After selecting and installing catalytic bead sensors, maintenance is an ongoing task that requires periodic attention to ensure a safe work environment - from General Monitors.
Calibration Could Save Your Life - A gas detector is a safety device. A properly functioning gas detector could be the difference between life and death. Making sure such a device is working properly on a regular basis should, without question, be a part of a scheduled maintenance program - from CETCI Magazine.

Planning and Designing Gas Detection Systems

New Separate and Comprehensive Page! The Planning and Designing of Gas Detection Systems should only be undertaken by Competent and Experienced Instrument or Fire and Gas Engineers. ICEweb's Planning and Designing of Gas Detection Systems – for Instrument and Fire & Gas Engineers page gives some useful technical advice on this.  It also has a reference source which provides further excellent engineering information on the subject - from Industrial Scientific Corporation


Addressable Gas Detectors

Addressable Gas Detection Systems - Analogue Gas detection systems serve many applications and are installed across the whole spectrum of industry. These systems have provided solutions to monitoring problems for many years gathering information on changing levels of gas for trending and logging applications or as part of safety warning/shutdown systems for Toxic and Flammable gas applications. From Extronics.


Air Duct Gas Detection

Monitoring of Air Ducts - Some really useful information here about gas detection monitoring in air ducts - thanks to Simrad Optronics and ICEweb sponsor PROdetec 
Gas Detection in Air Intakes - When it comes to monitoring of ventilation air, at air intakes, in ventilation ducts or at ventilation outlets, the trend has been towards lower trip levels and/or faster response times. This product information discusses these issues in order to help choosing the right detector for the task - from Simrad Optronics and ICEweb sponsor PROdetec
Detecting Combustible and Toxic Gases in HVAC Ducts - Air handling systems are used throughout industry to provide comfort and health in manned areas. Nevertheless, if unprotected, facility ventilation systems can transport combustible and toxic gases from a source area to other parts of the building, bringing the dangerous substances into non-hazardous areas, like control rooms, living quarters, electrical switch rooms, and equipment rooms. Because of the potential for the inadvertent transport of dangerous substances, government agencies, industry groups and many leading companies have established procedures for exhaust/ventilation system safety. One important element in the protection of these systems is gas detection - from General Monitors.


Catalytic Combustible Gas Detectors

Maintaining Catalytic Combustible Gas Detectors - Even the best of safety monitoring equipment requires periodic inspection. There must be a maintenance plan in place with documented procedures, a regular schedule of inspections, repair or replacement activity as necessary, problem reporting, etc. It is important to train employees to know when inspection is necessary and what type of maintenance procedures must be performed on a specific type or model of gas detector  - from General Monitors.
Catalytic Sensors – This Article covers Principle of Operation, Applications, Relative Sensitivity and Restrictions on Use - from Sensitron.
Understanding Catalytic LEL Combustible Gas Sensor Performance - In spite of the millions of combustible sensor equipped atmospheric monitors in service around the world, there is still a lot of misinformation and misunderstanding when it comes to the performance characteristics and limitations of this very important type of sensor. Understanding how combustible sensors detect gas is critical to correctly interpreting readings, and avoiding misuse of instruments that include this type of sensor.
Catalytic Combustible Gas Sensors - Catalytic bead sensors are used primarily to detect combustible gases. They have been in use for more than 50 years. Initially, these sensors were used for monitoring gas in coal mines, where they replaced canaries that had been used for a long period of time. The sensor itself is quite simple in design and is easy to manufacture. In its simplest form, as used in the original design, it was comprised of a single platinum wire. Catalytic bead sensors were produced all over the world by a large number of different manufacturers, but the performance and reliability of these sensors varied widely among these various manufacturers - from International Sensor Technology.


Calibrating Gas Sensors

Gas Sensor Calibration - Gas sensors need to be calibrated and periodically checked to ensure sensor accuracy and system integrity. It is important to install stationary sensors in locations where the calibration can be performed easily. The intervals between calibration can be different from sensor to sensor. Generally, the manufacturer of the sensor will recommend a time interval between calibration. However, it is good general practice to check the sensor more closely during the first 30 days after installation. During this period, it is possible to observe how well the sensor is adapting to its new environment - from International Sensor Technology.


Calibration Gas for Gas Detectors

Do Calibration Gases Have a Shelf Life? - Calibration is a vital and necessary step to ensuring the proper performance of any gas detector. The calibration process requires use of a known concentration of test gas, also known as span gas or calibration gas. Use of incorrect or expired calibration gas can result in improper calibration. This can result in unsafe operation, as well as improper diagnosis of instrument malfunction. This article will focus on disposable (non-refillable) calibration gas cylinders for both reactive and non-reactive gases - from Control Equipment.
Gas Calibration: Methane or Pentane? - Choosing the incorrect gas to calibrate your detector will make the readings inaccurate and potentially unsafe. This article explains which gas to use in order to ensure accurate and safe readings – from CAC.


Open Path Infra Red Gas Detectors

ICEweb has a Technical Information Page for Instrument and Fire & Gas Engineers dedicated to Open Path Gas Detectors, it covers Infra Red Line of Sight (Open Path) and Point Detectors Principle of Operation, Technology, Calibration and more!

The Benefits of IR Gas Detection for Oil and Gas Applications - Gem Bayless - Gas detection has been through a number of evolutions since the birth of the industry over 50 years ago. A major milestone in its history has been the introduction of Infrared (IR) gas detection, which uses a Hydrocarbon gases ability to absorb IR light at a pre-determined wavelength. Thanks to its notable value, which includes a fast speed of response (typically T90 in less than 5 seconds), fail-to-safety operation, immunity to poisons and ability to work in inert atmospheres, IR detection is fast becoming a popular method of detection - particularly within the oil, gas and petrochemical industries -from Honeywell and PetroOnline
Gas Detection Infrared Sensors Broaden Scope of Platform Gas Analysis - Jeff Markley - Catalytic detectors reveal the presence of combustible gases through a change in the resistance of the embedded coil - but their sensitivity can be affected by airborne contaminants. Infrared sensors allow open path detectors to detect gas up to 200 metres away - from Honeywell Analytics.
Reducing Costs and Enhancing Safety with Open Path Infrared (IR) Gas Detection  - It is fair to say that Infrared (IR) technology has revolutionised the gas detection market, providing a principle of detection that offers many tangible benefits in terms of performance, functionality and reduced ongoing costs. Since IR’s introduction into gas detection during the late 1970s, a variety of principles have subsequently emerged, the most impacting of which has been Open Path. This is a detection technique that allows gas to be monitored across a large range. Unlike a single Point IR device, an Open Path detector usually has two components with a beam of IR light between them, allowing this type of device to detect a gas cloud that drifts into the beam. This configuration provides the instant benefit of an increased chance of detecting a gas leak. Designed to monitor a diverse variety of Hydrocarbon gases, Open Path IR has a number of key benefits that add real value, when compared to solutions like catalytic bead detection. It is essential to consider the build, configuration and value of the Open Path devices currently available, when selecting a system, as they can vary considerably in terms of performance capability and ability to reduce ongoing costs - from Honeywell Analytics.
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Gas Detection Certification

From Singing to Sensing - IECEx Certifies Modern Gas Detectors and Sensors - Like a Canary in a Coal Mine - The use of canaries as gas detectors had been a mining tradition in the UK since 1911. Toxic gases such as carbon monoxide, carbon dioxide or methane in the mine would kill the bird before affecting the miners. Because canaries tend to sing much of the time, they would stop singing prior to succumbing to the gas, so alerting miners to the danger. As reliable as canaries might have been, the switch to electronic gas detectors actually made sense and brought greater safety. Technologies are evolving constantly and modern gas detection devices are state-of-the-art, extremely sophisticated devices that use sensors to identify potentially hazardous gas leaks. They are usually part of larger safety systems that can be found in a wide variety of locations such as mines, oil rigs, refineries, paper mills and industrial / waste water treatment plants. They are also widely used by firefighters. These devices often interface with control systems so that a process can be shut down automatically in dangerous situations. This is well worth a read - from IECEX.


Gas Detection using Laser Technology

Gas Detection using Lasers - A good tutorial on this new technology from Boreal Laser.


Gas Detection using Photoacoustic Infrared Technology

Photoacoustic Infrared Technology is the newest method of gas detection. It enables gases to be detected at extremely low levels due to its inherent stability and reduced cross-sensitivity- Thanks to MSA


Gas Detection in Gas Turbines and Compressor Stations

Fire and Gas Detection for Gas Turbines - Modern gas turbines are designed to burn light oils (Naphtha) or natural gas. Fuels and the lubricating oils along with cooling agents like hydrogen add-up to a high degree of hazard potential. For these reasons a multiple line of defence has to be established to guaranty protection against fire and explosion risks. Gas detection instruments and optical fire detectors are the central element in the protection systems - - from Draeger Australia.
Detecting Combustible Gas Leaks in Compressor Stations - In gas compressor stations, there is a high risk of fire and explosion due to a combination of intense heat, pressure and vibration. Gas detection solutions help to maintain safety in gas compressor stations. Ultrasonic, Infrared and Catalytic Bead gas detectors can be used alone or in integrated systems to help stabilize hazardous environments - from General Monitors.


Gas Detection Standards

AS/NZS 60079.29.4:2011- Explosive Atmospheres - Gas Detectors - Performance requirements of open path detectors for flammable gases.The objective of this Standard is to establish the specific requirements for design, construction and performance testing of electrical equipment for open path detection of flammable gases and vapours. It is complementary to AS/NZS 60079.29.1, which applies to the other detection techniques available for this purpose. It is intended to be read in conjunction with AS/NZS 60079.0 for its electrical protection. See a preview here.
Survey of Standards - Related to Gas Detectors - Bill Crosley and Simon Pate- What are the key standards for gas detectors? This paper lists the main world-area standards to which protection types are tested and certified. For combustible gas detector criteria, there is little to differentiate between FM 6310, 6320 (used mainly in the US) and the CSA C22.2 #152 (used mainly in Canada). Both are closely related to ANSI/ISA 12.13.01-2000. In those countries (mostly in Europe) that have adopted the IEC standards.  The IEC 60079-29 Series contains not only the hazardous locations requirements but also the gas detection performance requirements for both point and open path combustible gas detectors. In offshore toxic gas applications, the ISA standard is generally the defacto global standard for most world areas. Standards EN 50402, EN 45544, and EN 50104 are used in Europe and other world areas. Gas detectors are a critical part of the overall safety system. Therefore, all standards require the gas detector, the controller, and the output for the performance approval. Output is often the annunciation device. Be aware, though, that in many applications when a gas detector is connected to the process automation system it is not in full compliance with the requirements of FM6310,20 based on ANSI/ISA 12.13.01 or IEC60079-29 — the process automation systems are not evaluated against these standards.
IEC 60079-29-4  - Explosive atmospheres, Part 29-4: Gas detectors—Performance requirements of open path detectors for flammable gases.


Portable Gas Detection

Plant Safety Engineers take Aim at a Wireless Future - Dr.Patrick Hogan - Equipping the mobile worker with a personal gas monitor that not only can monitor a range of hazardous gases, but also report the worker’s exact location, continuously, in real time—over a wireless communications grid—represents one small step forward for today’s control room operator, yet one giant leap forward for plant safety - thanks to Honeywell Analytics and HazardEx.
Working Safely in Confined Spaces - Confined spaces pose various hazards for operators and can be found in a wide variety of industries and applications. A confined space can be defined by a number of factors; the space itself must be large enough for a worker to enter but is not suitable for continuous worker occupancy. A confined space is also defined as having limited openings for entry and exit. Examples of confined spaces found in industry include aircraft fuel tanks, underground utility vaults and wine fermentation tanks. Due to their small size, gas hazards can quickly build up in confined space environments. Some confined spaces may require permits to enter, owing to the fact that they contain potentially hazardous atmospheres or materials that have the potential for engulfment. Inwardly sloping walls or floors can also pose dangers, because they reduce the volume of the space, and may also require a permit to enter. Regardless of whether the area is permit required or not, all confined spaces should be treated as potential hazards -  from  Honeywell Analytics.

Portable Gas Detection Bump Testing

New Regulation Highlights Importance of Bump Testing -  Bump testing is a quick and essential test that ensures a portable gas detector is working properly. It involves exposing the device to a known concentration of gas/gases and checking its response and whether it alarms within its pre-defi ned parameters. When it comes to working with dangerous gases, a bump test really can mean the difference between life and death -  from Honeywell Analytics.


Photoionization Detectors

Photoionization Detectors - The photoionization detector (PID) utilises ultraviolet light to ionize gas molecules, and is commonly employed in the detection of volatile organic compounds (VOCs) - this comprehensive chapter from International Sensor Technologies covers;
Principle of Operation
Characteristics
Applications


 

Toxic Gas Monitors

Electrochemical Sensors - Electrochemical sensors operate by reacting with the gas of interest and producing an electrical signal proportional to the gas concentration. A typical electrochemical sensor consists of a sensing electrode (or working electrode), and a counter electrode separated by a thin layer of electrolyte. This comprehensive chapter from International Sensor Technology  provides an excellent overview of these sensors which are predominately used for Toxic Gas Monitors.
Simtronics Enhances GD1 Open-Path Toxic Laser Gas Detector Performance and Maximum Distance - Simtronics GD1 Laser Open-Path Detector has been enhanced with a stronger signal which increases the path length distance between the detector and transmitter from 50m to 75m; an increase of 50%. In addition, the considerably improved signal strength has increased the detector’s robustness and performance especially in extreme weather conditions such as ice and sand storms - from ProDetec.
An introduction to Toxic Gas Monitors - Industrial plants that manufacture chemicals, fertilizers, petroleum products, or, facilities that produce oil & gas, have to handle various toxic chemicals in their day to day operations. Many of these toxic chemicals are in the form of gases or vapors. This article will give a brief overview of the various kinds of toxic gas detectors used to detect these poisonous materials - From  Abhisam Software


Ultrasonic Gas Leak Detection

Ultrasonic Leak Detection - The First Stage in Gas Detection - These sensors will detect gas at‘the speed of sound’ and do not need to be in the gas cloud to operate successfully. Ultrasonic gas detectors have been designed to detect pressure gas leaks from all gases, this includes the 35% of Hydrocarbon Leaks which go undetected in the North Sea (Source UK HSE) -  thanks to ICEweb sponsor PROdetec and Emerson Process Management
Ultrasonic Detection Overview - Ultrasonic (acoustic) gas leak detection technology functions through the constant monitoring of wide areas by advanced acoustic sensors specially tuned to process ultrasound emitted from pressurized gas leaks. This detection technology has several advantages (a) It does not have to wait until a gas concentration has accumulated to potentially dangerous concentrations and (b) It does not require a gas cloud to eventually make physical contact with a sensor, and the response is instantaneous for all gas types - from Emerson Process Management.
Ultrasonic (Acoustic) Gas Leak Detection Technology - Ultrasonic (acoustic) gas leak detection technology works by listening for ultrasound emitted from pressurised gas leaks. Instead of measuring a concentration level in LEL as traditional gas detectors (point and open path detectors) the ultrasonic gas leak detectors raise an instant on/off alarm if a leak is detected. The ultrasonic gas leak detectors do not have to wait until the gas concentration has accumulated to a potentially dangerous gas cloud, they react instantaneously. This means that unlike traditional gas detectors, ultrasonic detectors can detect gas leaks at the speed of sound without being affected by wind directions or gas dilution.  Instead of measuring a concentration level in LEL, the ultrasonic (acoustic) gas leak detection method is based on the so-called leak rate. This makes detection more reliable and efficient as it is possible to verify the performance of the detection system - This link also includes a case history, detection coverage, installation practice, background noise, gas leak definition and frequently asked questions - from Gassonic.
Technology Status Report on Natural Gas Leak Detection in Pipelines -  The reliable and timely detection of failure of any part of the pipeline is critical to ensure the reliability of the natural gas infrastructure. This report reviews the current status of the technology for leak detection from the natural gas pipelines. The first part briefly reviews various leak detection methods used in the natural gas pipelines. The second part reviews the optical methods used for natural gas leak detection, and the final part reviews the potential sensors that can be used with optical methods.


Gas Detection Courses

E-learning course on Gas Monitors -From Abhisam Software- This course includes the whole range of gas detectors and monitors providing training covering the following;
  • Introduction to Gas Monitors
  • Basic Concepts- Fire Triangle, Lower Explosive Limit & Upper Explosive Limit, Flash Point, Accuracy & Inaccuracy, Calibration, Linearity, Repeatability & Accuracy
  • Explosive & Toxic Gases - Regulatory & Standards Bodies, Terminology, Time Weighted Average, Short Term Exposure Limit, IDLH & Ceiling Limit, REL, PEL & TLV ---What do they mean?
  • Types of Gas Monitors - Catalytic Combustion, Electrochemical, Semiconductor, Infra Red, Photo Ionization
  • Gas Monitoring Systems - Dedicated and Open Systems
  • Installation, Calibration & Maintenance - Planning & Installation of gas monitors, Calibration & Testing, Maintenance