Gas Detection Systems, Gas Detection Equipment and Gas Monitoring Systems
OX-AN? have provided the following information for gas detection systems as simple information guidance only. Please refer to published documents. OX-AN? cannot be held responsible in any way for the use of this data.
Whether you refer to them as gas detection systems, gas detection equipment or gas monitoring systems, they have come a long way in a few centuries. Before the 19th century, when the effects of various gases on human health were not yet well established, gas detection methods were typically less precise. In the 19th century, coal miners introduced canaries into the mining tunnels as a safety precaution against life-threatening gases such as carbon monoxide, methane and carbon dioxide. The canaries a crude for of gas detection equipment, would then stop singing and eventually die when not removed from areas with harmful gases, signalling to the coal miners that it was time to leave the mines and escape from the presence of harmful gases. In the 1980s and 1990s gas monitoring systems utilised chemically-infused papers to detect carbon monoxide, with the papers turning brown in the presence of the gas. Soon after, electronic gas detection systems were introduced to detect, monitor and alert people of gas leakages and potential gas hazards.
The performance and cost of gas detection systems has improved immensely over the years, and more varied gas sensors have now been incorporated into a broad array of gas monitoring systems. For instance, gas detection systems have been installed in automobiles to help with engine emissions control and to boost passenger safety and comfort. Equally, gas detection equipment incorporating carbon dioxide detectors have been installed in residential and commercial buildings to boost the effectiveness of demand-controlled ventilation systems. Likewise, sophisticated gas detection systems have been devised for use in medical operation rooms and for diagnosis, monitoring and treatment procedures. Gas detection equipment, alarms and sensors for carbon monoxide and many other harmful gases have been also availed for domestic and office use, and for legal investigations. Furthermore, the complexity of gas detection systems has changed greatly over the years. For example, while initial electronic detectors were designed for detecting one type of gas, modern detectors can sense several combustible or toxic gases simultaneously.
What Are Gas Detection Systems?
Gas detection systems are front-line devices that provides the earliest hint of the release of a dangerous gas. The systems gas detection equipment detect the presence of gases in designated areas and are typically used as part of an extensive safety strategy. Gas detection systems are typically used to monitor flammable, toxic, combustible and oxygen depleting gases. When installed in a place, the gas detection equipment will detect a gas leakage and then interfere automatically with the gas control system in order to shut down the gas flow. Alternatively, gas detection equipment sensors may sound warning alarms to operators or residents of an area where gas leakage is occurring in order to give those individuals a timely opportunity to leave the area.
Top-notch gas detection systems should only be used as part of an all-inclusive safety management plan that must be in place in any residential, commercial or industrial settings where gases are used or handled. In fact, for gas detection systems to be effective, they must not only have proper layouts and designs, but should also come with standardised user guidelines addressing the questions of how the gas detection systems should be configured eg how many sensors should be used for different settings. Users must also put in place measures for the timely application of real-time gas detection equipment data and alerts obtained from the gas sensors.
What Types of Gases Require Gas Detection Equipment?
A gas is any substance that exists normally in the gaseous state at ordinary temperatures and pressures, while a vapour is a gaseous form of any substance that normally exists as a liquid or solid at ordinary temperatures and pressures.
Fumes are airborne dispersions that are made up of minute particles originating from solids (commonly oxides) as result of chemical reactions between the solids and oxygen. The types of gases and vapours that require gas detection equipment include:
1. Asphyxiants: These are gases and vapours that cause suffocation through oxygen displacement (such as carbon monoxide and hydrogen) or through the interference with the ability of human blood to transport oxygen (such as carbon monoxide).
2. Corrosives (Irritants): These are gases that cause tissue inflammation through their chemical actions. They include ammonia, chlorine, ozone, and sulphur dioxide.
3. Toxic Gases: These are gases that are poisonous to one or many body tissues (or organs). They include carbon sulphide, carbon monoxide and chloromethane.
4. Carcinogens: These gases cause cancer. An example is vinyl chloride.
5. Central Nervous System Depressants: The gases disturb the central nervous system. Examples are acetone and benzene.
6. Combustibles and Flammables: Generally, combustibles are liquids that can reach their flash points at temperatures between 100 degrees F and 200 degrees F, while flammables specifically reach their flash points under 100 degrees F and often form explosive mixtures with air at just 13-percent of the gas or less. Examples include gasoline, propane and methane.
Types of Gas Monitoring Systems
There are several gas detection systems which inform the designs and functionality of different gas detectors. Gas detection equipment sensors come in a broad range of shapes, colours, sizes, and sensor configurations. The most common gas detection equipment classes are:
1. Combustible Gas Sensors
2. Toxic Sensors
3. Oxygen Sensors
Gas Monitoring Systems with Combustible Gas Sensors
Gas monitoring systems with combustible sensors are effective in detecting explosive atmospheres. They include catalytic combustible gas detectors, metallic oxide semi-conductor detectors, and infra-red combustible sensors.
i. Catalytic Combustible Gas Detectors
Supplied with sensor chambers where any leaked combustible gas is actually burned and detected, the sensors in these gas monitoring systems react to almost all combustible gases and provide impressive linearity. These gas detection systems are suitable for gas concentrations of 1,000-50,000 PPM because their resistance to %LEL is small. While these sensors’ flame arrestors will typically prevent ignition of most gases (except acetylene), it is usually prudent to check gas monitoring systems manufacturer instructions for the recommended hazard areas where any type of catalytic combustible sensor can function before making a purchase.
The most common gas detection systems certification for catalytic combustible gas sensors is Class I, Div I, Group ABCD atmospheres, but other forms of gas monitoring systems certifications may also be invaluable. In addition, gas detection equipment with these sensors should not used for detecting toxic levels of gases because they cannot measure trace quantities of gas, such as levels below 200 PPM. Limitations of gas detection equipment with catalytic combustible detectors include:
a. The sensors are easily damaged by silicone, lead and other catalytic poisons.
b. Sensor readings can be affected by water vapour condensation and humidity.
c. The sensors give poor responses to low-energy hydrocarbon gases such as vapours from diesel fuels, commercial jet fuels, kerosene and oil vapours.
d. The sensors are not suitable in acetylene atmospheres and only give accurate detections when oxygen content of air is at least 14-percent.
e. They also lose their linearity after only one year of operation.
ii. Metallic-Oxide Semi-Conductor Detectors For Combustible Gas
The Solid State (MOS) combustible gas detectors have been used for in gas detection systems for decades and boast of an impressively extended operation life (three to five years). The detectors are also rugged and recover effectively from very significant concentrations of gases that often damage many types of detectors in other gas monitoring systems. Gases are detected through a chemical reaction as soon as the gas comes into direct contact with the detector.
The most common material in gas monitoring systems with these sensors is Tin Dioxide, whose resistance is around 50 kΩ but drops drastically to around 3.5 kΩ as soon as it comes into direct contact with the target gases. Metallic oxide semiconductor detectors are commonly used to detect oxygen, hydrogen, alcohol vapour and carbon monoxide in a whole host of different gas monitoring systems.
Limitations of MOS sensors include:
a. Their readings can be affected by condensed water vapour and humidity.
b. They require high oxygen concentrations to give accurate readings, although not as high oxygen amounts as catalytic detectors.
c. They are made of some heating elements that consume a lot of power and require larger battery packs.
d. They respond to most solvents, HFCs and VOCs, but lack specificity for any one gas compound.
iii. Infra-Red combustible Sensors
The most common infra-red detectors in gas monitoring systems are either infra-red point sensors or infra-red imaging sensors. Infra-red point (IRP) sensor type gas detection systems use infra-red radiation that passes through a designated volume of gas, creating an energy beam whose wavelength depends on the specific gas. The detectors in this type of gas detection equipment allow gas detection without necessarily being in the gas itself and can be used for remote gas detection. Commonly, infra-red point sensors based gas detection systems are used to detect infrared active gases such as carbon dioxide, water vapour and a number of hydrocarbons, and are greatly beneficial in refineries, chemical plants, gas turbines and wastewater treatment facilities.
The infrared imaging gas sensors in gas monitoring systems apply either active or passive detection techniques. In active gas sensing, infrared detectors send laser beams across scenes of suspected gas leakage and create images of backscattered light whose properties depend on the characteristics of the scanned gas. In passive infrared sensing gas detection equipment, spectral changes at every pixel of the images resulting from infrared scans are analysed for particular spectral signatures that are indicative of targeted gases. Infrared detectors are very effective in acetylene or low oxygen atmospheres, but will not detect hydrogen and are quite expensive for deployment in gas detection equipment.
Gas Detection Equipment with Toxic Sensors
These are sensors that are capable of detecting toxic concentrations of gases. This type of gas detection equipment includes electrochemical sensors, toxic-range metallic oxide semiconductor sensors, photo ionization sensors and ultrasonic detectors.
i. Electrochemical (Wet-Chem) Sensors for Toxic Gases
Gas monitoring systems with wet-chem sensors are chemically-specific and are usually designed for detecting one of at least 30 specific gases, including ammonia, chlorine, nitrogen dioxide, carbon monoxide, nitric oxide, carbon dioxide, sulphur dioxide, hydrogen sulphide and hydrogen cyanide. The specific gas to be detected is indicated on the instrument and on the technical information sheet that comes with the gas detection equipment. Due to their good linearity, gas monitoring systems with these detectors are highly accurate and precise to the gases they are designed to react to, and will measure both high and low quantities of the gases.
In gas monitoring systems, the typical lifespan of an electrochemical sensor depends on the gas measured, with most common toxic
gases detected for up to 1 year, while carbon monoxide and hydrogen sulphide being detected for up to 2 years of sensor operation.
The limitations of Wet-Chem gas detection systems include:
a. Their electrolytic fluids may freeze when temperatures fall below 0 degrees centigrade.
b. Some are pressure sensitive and are adversely affected by changes in altitude.
c. They are prone to abnormal readings, especially because of interferences by gases that are not being measured. For instance, oxidizers like ozone, chlorine and chlorine dioxide may interfere with toxic sensors for hydrogen sulphide and carbon monoxide gas detection equipment.
ii. Toxic-Range Metallic-Oxide Semiconductor Detectors
Gas monitoring systems with metallic oxide semiconductor sensors are specifically designed to detect toxic concentrations of gases within gas monitoring systems. Their modes of operation in gas detection systems are similar to combustible MOS sensors, but they react to very low PPM levels for a broad range of gases, including toluene, styrene, ammonia, carbon monoxide, gasoline, hydrogen sulphide, solvents and hydrocarbons. Nonetheless, the sensors cannot detect sulphur dioxide and carbon dioxide, and are incapable of indicating either the concentration or the type of gas that is detected with this mode of gas detection equipment. Hence, their primary role is to detect gas hazards and call attention of sensor operators to potential toxicity.
iii. Photo Ionization Detectors (PIDs)
These detectors are commonly used in gas detection systems by safety professionals, industrial hygienists, environmentalists, and other professionals involved in detecting health and atmospheric hazards. They can perform effectively for 1-3 years depending on extent of use, but are very expensive to use as multi-sensor instrum
ents because a single lamp replacement goes for $300 to $1400.
iv. Ultrasonic Detectors
These sensors are supplied with acoustic detectors in gas monitoring systems for measuring background noise when high-pressure leaks occur. The detectors can measure the rates of gas leaks, but cannot indicate the concentrations of the measured gases. They are used to in gas detection systems to detect toxic gas leaks in outdoor pipelines, gas metering and compressor stations, and gas-turbine power plants.
v. Holographic Gas Sensors
Another type of gas detection equipment uses reflected light to detect changes in polymer film matrices containing holograms, the sensors can identify specific gases. However, the detectors in these types of gas monitoring systems require sources of illumination, such as lasers and white light, and CCD detectors (or observers) in order to operate.
More about how gas detectors work here
Gas Monitoring with Oxygen Sensors
These are the only sensors used in gas detection systems with true chemically-specific detection. In oxygen gas monitoring systems, they operate in similar fashion as electrochemical detectors, but are quite susceptible to freezing and altitude changes. Their nominal operational life is 1-2 years. Oxygen sensors in gas monitoring systems must never be used to detect toxic gases because it takes around 60,000 PPM of any toxic gas to push the oxygen levels in the detectors from the normal 20.9-percent to the 19.5-percent alarm point. When a toxic gas reaches 60,000 PPM, it is already at a level where it can kill, making the detection of the toxic gas with an oxygen sensor a futile venture.
Selecting Gas Detection Systems & Gas Detection Equipment
When selecting gas detection systems, you should consider the following factors:
1. Mechanism of Operation of the Sensor: Most gas detectors operate by diffusion, allowing air to enter the detector cell before the gas can be detected. Electrochemical detectors purely rely on diffusion. Alternatively, a detector may operate through remote sensing, in which case the gas to be detected must not enter the detector before sensing can begin.
2. Complexity of Calibration: All sensors must usually be calibrated according to manufacturer recommendations. Sensors, just like other electronics, may fail to give accurate detection if they are not calibrated. Therefore, when selecting sensors for residential and commercial settings where there may be no full-time expert to do frequent calibrations, it is important to choose an easy-to-calibrate detector.
3. Design Characteristics: The best gas sensor should be rugged enough and easy to carry in order to allow for convenient usage during field work. The components must also be strong enough to withstand rough handling, drops, misuse, exposure to the elements and jolts. The gas detection equipment alarm systems should be loud enough to be heard across a larger area while their batteries should be either rechargeable or disposable but capable of supplying enough power over the span of 10-12 hours a day. Besides, gas detectors for confined spaces should be portable (hand-held/worn on belt). The buttons, switches and belts must be firmly fixed and not easy to knock off their positions; while displays should be easy to read and large enough to see from a distance. Additionally, the right sensor should have easy-to-understand abbreviations.
4. Reliable Electronics Information: Gas sensors for are used to make life and death decisions, hence all electronics information provided should be useful and reliable. When choosing gas detection equipment, you must confirm the reliability of its response time and the potential effects of its reading drifts, sensitivity, precision, accuracy and radio frequency (RF) interference on its utility for gas detection systems.
5. Approvals and Certifications: A top-class gas detector must be approved and certified by an independent laboratory.
6. Gas Detection Equipment Ease of Use: Is the detector easy to use? Is it simple and trouble-free to operate? Are the abbreviations and displays easy to read and understand? Can the switches and buttons be used even with your gloves on? A one-switch operation and a reliable battery and alarm system are critical factors to consider when choosing a gas detector system.
Finally, when selecting a gas detection system, gas detection equipment or gas monitoring systems
, avoid the temptation to be swayed by fancy packaging and sophisticated technology. You must choose a system that suits your needs and which is cost-effective.