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Introduction
Contains descriptions of gas analyzers and monitors, lists of gas analyzer and monitor manufacturers, and types of gas analyzers and monitors.
You will learn:
What is a Gas Detector?
Types of Gas Detectors
Uses for Gas Detectors
How Gas Detectors Work
And much more …
Chapter 1: What Are Gas Detectors?
Gas detectors are analyzers and monitors that are designed to detect the concentration of gases using various types of sensors including combustible, infrared point, ultrasonic, photoionization, metal oxide semiconductor (MOS), and electrochemical sensors. The function of the sensors is to measure the concentration of gases in a particular area and generate an output reading that can be recorded and measured.
The two types of gases that gas detectors measure are combustible and toxic. Aside from its sensor, a gas detector includes a control unit and alarm system with the sensor being at the center of the system and the means for identifying the presence of gases.
Chapter 2: Types of Gas Detectors
The many types of gas detectors have the singular goal and purpose of detecting one or more gases in different environmental conditions. Gas detectors are differentiated by their operational mechanism, which are designed to meet the needs of different industries that require unique gas detection methods. The general categorizations for gas detectors are fixed and portable where portable detectors are handheld while fixed gas detectors are mounted in various areas as part of a gas detecting system.
Electrochemical Gas Detector
Electrochemical sensors operate by reacting with the analyte and producing an electrical signal. Most electrochemical gas sensors are amperometric sensors, generating a current that is linearly proportional to the gas concentration. The principle behind amperometric sensors is the measurement of the current-potential relationship in an electrochemical cell where equilibrium is not established. The current is quantitatively related to the rate of the electrolytic process at the sensing electrode or working electrode, whose potential commonly is kept constant using another electrode, known as the reference electrode.
The housing casing allows gas in the liquid to flow passed the sensor but blocks the liquid in the electrolytic liquid. When the gas reaches the working electrode, an electrochemical reaction causes a flow of electrons between the working and counter electrodes. The generated electrical current is proportional to the concentration of the target gas in the liquid. The current is amplified and processed to provide a reading for the user in parts per million or percentage of volume.
Although electrochemical gas detectors are designed to detect one particular gas, they can be affected by cross sensitivity, which is the presence of another gas that may be blocking the programmed gas. In order to avoid cross sensitivity, filters and bias voltage are used during the gas detectors operation.
Catalytic Bead Gas Detector
Catalytic bead gas detectors, also known as Pellistor sensors, have a catalytic material that is sensitive to flammable gases and an inert compensator element. They have a small bead coated with a catalyst, such as platinum or palladium, an uncoated reference bead, and two electrodes. The beads are placed at the opposite end of a Wheatstone bridge circuit that measures changes in electrical resistance between the beads.
When gas comes in contact with the catalyst bead, the catalyst causes the gas to burn at a lower concentration and temperature than that of the uncoated bead. The heat that is produced is proportional to the concentration of gas in the air. The energy from the reaction causes a change in resistance in the catalytic bead while the uncoated bead has a steady unchanged resistance. The differences in the levels of resistance is measured by the Wheatstone bridge and indicates the presence of a combustible gas.
The primary function of catalytic bead gas detectors is the detection of combustible gases. They are from the family of gas detectors that are referred to as pellistors, which are solid state devices.
Infrared Gas Detectors
An infrared gas detector has an infrared light source, an optical filter, and an optical infrared receiver. The sensing channel and reference channel absorb infrared heat at a specific wavelength. As gas flows through an infrared gas detector, hydrocarbon molecules absorb the infrared energy. The receiver in the gas detector detects the drop in energy as a measure of the amount of hydrocarbon gas. Infrared gas detectors use two wavelengths of infrared energy, sensing and reference, for active absorption while reference wavelength measures the effects of temperature, humidity, and moisture or dirt on the optical filters.
The two classifications for infrared gas detectors are open path and point, which differ by how they measure the amount of combustible gas. A point detection infrared detector measures the amount of gas at a fixed set point while an open path detection infrared detector has separate transmitters and receivers that measure the amount of gas between two points that can be a distance apart.
Infrared gas detectors have become very popular because they do not require frequent calibration and the need for oxygen in order to detect hydrocarbon gases and have the additional advantage of not being poisoned by oils that are common to offshore drilling rigs. A microprocessor in an infrared gas detector monitors the source and receiver, the status of which it sends to a controller.
Photoionization Gas Detector (PID)
Photoionization gas detectors are commonly used to detect volatile organic compounds (VOCs), which are chemical compounds that affect human health and the environment. Ultraviolet light ionizes the molecules of the over 700 VOCs that pass through the PID, which excites the molecules and causes them to lose electrons that become positively and negatively charged ions that generate an electric current. The presence of a VOC is indicated by a rise in the strength of the electric current.
The reading from a PID is achieved by the ions that are driven by a bias electrode and collected at a collection point. The current of the ions is amplified and converted into a digital meter readout as parts per million (ppm).
PIDs require regular calibration to ensure their accuracy, which makes them capable of detecting the lowest concentration of VOCs. Although PIDs are an exceptional detecting device that have wide industrial use, they can detect VOCs but are unable to differentiate between the different types such as propylene and acetone or any other VOCs. Their function is to let users know that a VOC is in the area. It is for this reason that specific gas detectors are used for detection of certain gases.
Ultrasonic Gas Detector
Ultrasonic gas detectors use acoustic sensors to detect and monitor the sound of a leak. The sensors of an ultrasonic gas detector react to leaking gas that produces sounds at an ultrasonic frequency. The rate at which the gas leaks is dependent on the size of the leak and the pressure under which the gas is stored or moving. Pressurized gas produces ultrasounds of 25 kHz up to 100 kHz, which ultrasonic gas detectors can detect the gases' audible noise.
Aside from their use as a safety device, ultrasonic gas detectors are a useful maintenance tool since the detectors can alert staff to developing leaks before they become a serious problem. Ultrasonic leak detectors are used for air leaks, gas leaks, and vacuum detection. They are an essential tool for detecting problems with bearings and pumps.
Semiconductor Gas Detector
Semiconductor gas detectors use a gas sensitive resistive film, a platinum heating element, and insulation. The resistive film uses tin or tungsten oxide combined with catalysts and dopants to increase the sensitivity of a semiconductor gas detector, since the combined materials provide higher sensitivity at lower temperatures. The critical part of a semiconductor gas detector is the sensing layer or film, since it is the part of the detector that reacts to different gases in a unique way. Electrodes connected to the sensing layer collect and transmit electrical changes in the sensing layer in order to identify the type of gas and its concentration.
When a semiconductor gas detector is exposed to gas, the molecules of the gas react to the metal oxide and become charged ions that change the resistance of the film, a change that is dependent on the physical properties of the oxides and the geometric characteristics of the sensing layer as well as the temperature at which the reaction occurs. The interaction between the gas molecules and the film is monitored by the electrodes and converted to a gas concentration, which can be measured and used to determine the amount of gas.
Single Gas Detectors
Single gas detectors are programmed to monitor one gas, such as carbon monoxide, ammonia, hydrogen cyanide, or sulfur dioxide. They are more compact gas detectors and lighter than multiple gas detectors and can be carried or worn. Single gas detectors are referred to as disposable gas detectors and have a useful life of two to three years, which removes the need for replacing or maintaining them.
The single button operation of a single gas detector makes them user friendly, cost effective, and highly reliable. A single gas detector has one sensor, and users can set the alarm set point to fit their gas detection needs. Included in the multiple screens of a single gas detector is a countdown screen to indicate when the life of the detector will expire. Once a single gas detector is activated, it remains on without the need for a battery charging and turns off when it reaches the end of its useful life.
Sustainable single gas detectors are much like any other form of gas detector in that they can be repaired, maintained, and are fully serviceable with easy calibration. Unlike single gas detectors with a limited useful life, sustainable gas detectors are made to last using heavy duty and highly resilient materials.
Common uses for single gas detectors include:
Nitrogen Applications – Although nitrogen is nontoxic, it can drop the oxygen level in an environment.
Boiler Rooms – A common problem in boiler rooms is carbon monoxide (CO) poisoning, which can be due to poor boiler maintenance, an obvious situation requiring a gas detection monitor.
Utility Companies – The nature of the work of utility companies requires the protection of workers who depend on single gas detectors.
Refineries – In the refining industry, hydrosulfide (H₂S) poses a significant problem due to the use of sour oil.
Cooling – Ammonia (nitrogen trihydride or NH3) is a natural coolant and is common in installations and agriculture applications. NH3 is used as a cooling gas and for producing fertilizer and is absorbable through the skin.
Carbon Monoxide (CO) – Carbon monoxide is a colorless, odorless, and tasteless gas or liquid that is very dangerous and can cause illness and death.
Other conditions where single gas detectors are used are Ozone (O₃), Hydrogen Peroxide (H₂O₂), and Phosphine (PH₃) detection.
Multiple Gas Detectors
Multiple gas detectors are capable of detecting several different gases depending on their programming. They are available in many sizes, shapes, and types of sensors and can detect several gases at the same time. Common types of multiple gas detectors are configured to detect carbon monoxide, hydrogen sulfide, combustible gases, and oxygen. Multiple gas detectors can have several sensors depending on the design and configuration of the detector. Sensor designs are available for detecting VOCs in conjunction with flammable gases.
As with single gas detectors, multiple gas detectors are capable of having a set of sensors that specifically meet the needs of a project or application. Manufacturers work with their clients to develop custom multiple gas detectors that are specially designed for unique functions. Every aspect of a multiple gas detector can be planned, configured, and assembled to meet a customer’s special needs.
The basic purpose of all gas detectors is to provide a safe and clean environment where workers are protected. Multiple gas detectors fulfill that objective by detecting gases in the atmosphere and measuring the supply of oxygen to ensure that there is air for workers to breathe.
In addition to detecting dangerous and harmful gases, multiple gas detectors can detect lower and upper explosive levels (LELs and UELs) of combustible gases, which is the lowest and highest concentration of a vapor or gas that can explode if an ignition source is present. The detector reads the amount of gas and how much is necessary for ignition, which is presented as %Volume. A 0% volume reading means that no gas is detected while a 100% reading means a gas has reached its LEL.
Multiple gas detectors are portable and worn in a person’s breathing zone, which is the area around the mouth and nose. This ensures the detector is examining the air that is being breathed. In most cases, workers place a detector on their collar or lapel. The mobility of multiple gas detectors makes it easy for workers to walk through an area unencumbered.
The most common sensors for multiple gas detectors are electrochemical and catalytic, which produce readings on the detector’s monitor. The alarms on multiple gas detectors are audible, visible, or vibrations with some versions producing all three. This particular configuration is used in conditions where there is noise or poor visibility.
Unlike single gas detectors, multiple gas detectors are reusable and have a long useful life. When not in use, they are stored in a protected secure area where they can recharge. Multiple gas detectors are regularly recalibrated to ensure the accuracy of their readings. Docking stations for multiple gas detectors perform bump tests by exposing sensors to gases to ensure the detector is taking proper readings.
Fixed and Portable Gas Detectors
A common division of gas detectors is fixed and portable, with fixed referring to gas detectors that are permanently installed in a stationary location. Portable gas detectors are carried or clipped to a person in a vulnerable area. The key differentiating factors between fixed and portable gas detectors is their design, applications, and functionality.
In most cases, several fixed multiple gas detectors are installed throughout a location to ensure complete coverage to create a gas detector system. They are designed for industrial and manufacturing locations that have several types of gas present. Portable gas detectors are designed for a single person and have limited coverage, which is why they are worn close to the breathing zone.
Fixed gas detectors have a limitless power supply from electrical mains and have backup batteries for power outages. Their power supply ensures constant monitoring and protection against failure. Portable gas detectors have disposable batteries or rechargeable batteries, which allows them to operate independently and autonomously. This aspect of their construction makes them flexible and easily accessible.
The majority of fixed gas detectors are larger and heavier due to their housing and installation method. Their larger size enables them to monitor a wider area with a larger and easy to read display. An additional benefit of the larger size of fixed gas detectors is their ability to have a broader detection range with higher sensitivity, which makes it possible for them to detect very low levels of gas in a wider area. By contrast, portable gas detectors are smaller, have a limited range, lower sensitivity, but are capable of detecting concentrations of gas at a personal level.
Chapter 3: Explosion Proof Gas Detectors
A select group of gas detectors are explosion proof gas detectors that have the same capabilities as other forms of gas detectors with the added benefit of being explosion proof. They are available in fixed and portable designs with a tough and highly durable housing that is capable of withstanding the harshest and most intense conditions.
In order for a gas detector to be classified as explosion proof, it has to meet the standards of ATEX, an abbreviation from French of ATmosphère EXplosible, which, in English, is explosive atmospheres. ATEX is a certification organization that is associated with the European Union. Its directives outline the necessary testing methods for a device, equipment, or component capable of withstanding explosive atmospheres. The standards for ATEX have been accepted by the American National Standards Institute (ANSI) as outlined in ANSI/ASA 12.13.01-2013.
The development and use of explosion proof gas detectors is in relation to the nature of other forms of gas detectors that may serve as an ignition source. It is for this reason that manufacturers emphasize and recommend the use of explosion proof gas detectors, which are certified as non-combustible computing and monitoring devices.
The use of explosive gas detectors is in accordance with ATEX classification system that divides hazardous areas into zones that define the presence of explosive materials for each zone or area. The zone classifications from ATEX are zones 0, 1, 2, 10, 11, 20, 21, and 22.
Zone 0 – With zone 0, explosive gases, vapors, and mists are constantly present and require the use of category 1 explosive protection devices.
Zone 1 – To have a zone 1 classification an environment has intermittent presence of explosive mixtures and uses category 1 or 2 equipment.
Zone 2 – Zone 2 is the least stringent of the three classifications and is defined as areas where it is unusual, abnormal, and infrequent that explosive gases are present. These areas can use all categories of gas detectors.
Zone 10 – Zone 10 makes reference to the continuous presence of dust for long periods of time.
Zone 11 – Zone 11 also makes reference to dust but is in regards to short term exposure to dust deposits.
Zones 20, 21, and 22 – Zones 20, 21, and 22 describe the frequent, intermittent, and abnormal presence of dust.
Gas detectors for explosive environments have point protocols and are infrared, electrochemical, catalytic, PID, or ultrasonic sensors. Under article 500.7(K) of the National Electrical Code (NEC), LEL detectors are required to be used for the protection of hazardous locations that have limited public access and highly trained professional workers. Article 500.7(K) specifies the frequency of calibration, shutdown criteria, alarm criteria, and proper installation locations. Like ATEX, the NEC has classifications for locations that require the use of an explosive gas detector with more specific stipulations for Class Is.
National Electrical Code Location
Class I – A class I environment has flammable gases, vapors, or mists in enough quantities to produce an explosive or volatile mixture
Class I, Division 1 – Ignitable materials are present under normal working conditions and exist frequently because of repairs, maintenance, or leakages.
Class I, Division 2 – Combustible materials are handled, processed, and used in containers and can only escape under abnormal operating conditions. Such locations have ventilation, which can be hazardous due to failure. Adjacent locations may be exposed to volatile materials due to failure of ventilation systems.
Class II – As with ATEX 10 and 11, class II of the NEC codes is in regard to the presence of dust.
Class III – Class III describes the presence of fibers or flyings
The National Fire Protection Association (NFPA)
One of the many reputable agencies that assists with guidelines for gas detectors is the NFPA, which has developed 300 codes, standards, and guidelines regarding safety procedures. The organization developed a popular warning safety square or fire diamond that serves as a quick reference regarding substances that pose a hazard. The description of the various hazardous levels is contained in NFPA 1991, NFPA 1992, NFPA 1994, and NFPA 2112.
Explosion proof gas detectors have housings and enclosures that are designed in such a way that they are capable of containing, controlling, and venting flashes or explosions. They are constructed of stainless steel or cast aluminum that can safely contain the explosions of flammable gases.
Intrinsically safe gas detectors have electrical circuits and wiring that does not release enough energy or produce high enough temperatures to cause an ignition. They do not require a special enclosure, have safety barriers and are used for low power applications.
Leading Manufacturers and Suppliers
Chapter 4: Gas Detector Systems
As critical and essential as gas detectors are, they are only a small portion of a more complex and complicated gas detecting system where each of the components work together for the protection of working conditions and workers. Fixed gas detectors are used as warning systems with various forms of alarms to inform occupants of the dangers of vapors, gases, and mists in an environment.
The NEC stipulates the requirements for a gas detection system, which must adhere to Class I, Divisions 1 or 2 of the NEC gas detector codes. Included in the standards is an identification of the gases or vapors to which people could possibly be exposed, with hydrogen gas required to be specifically listed and identified. To be classified as a gas detection system, it must be permanently wired, installed, and mounted and not include portable gas detectors.
Fixed system gas monitoring is an automatic response system designed to warn workers of the presence of lethal or volatile concentrations of gas. They are designed to shut down a system when a set alarm level is reached. Gas detection systems are built to avoid human errors or the possibility of missing detections. Included in gas detector systems are point gas sensors that monitor combustible gases, vapors, and mists at a specific point and fall within the LEL or LFL range of the system. Gas detection systems can use open path sensors that have a longer absorption path length and are capable of measuring gas concentrations across a wide-open area but are required to include point detectors for greater accuracy.
The use of a gas detection system is limited to enclosed areas with inadequate ventilation, building interiors, enclosed spaces, and the interiors of control panels. The definition of inadequate ventilation has been revised by the NEC in Code 500.7(K)(2) to state:
A location, enclosed space, or building that is classified as a Class I, Division 1 location due to inadequate ventilation, that is provided with a combustible gas detection system, shall be permitted to utilize electrical equipment, installation methods, and wiring practices suitable for Class I, Division 2 installations. Sensing a gas concentration of not more than 40% of the lower flammable limit or a gas detector system malfunction shall activate an alarm that is audible or visual, or both, as is most appropriate for the area. NEC Code 500.7(K)(2)
Gas detection systems provide an early warning regarding toxic or combustible gases and include a set of gas detectors, a centralized control system, and a warning system, such as strobe lights or warning horns. The controller powers the system, monitors the values of the detectors, and includes data logging. Although wired systems are still widely used, the majority of new gas detector systems are wireless, which allows users to reposition the detectors as conditions change.
Chapter 5: Leak Detection VS Gas Detection
Although there is some crossover between leak detection and gas detection, the two systems have different objectives but can work together. While gas detectors monitor the concentration of gas in an environment, leak detectors are capable of detecting any size crack, deformation, or break in a piping system. They use micropulse sonar, hydrostatic testing, tracers, infrared, and laser technology.
One of the major functions of a leak detection system is for finding leaks in water pipelines during repairs and installations. The types of leak detectors used for water lines are the same as those used for gas and liquid leaks, which are differentiated by the types of leaks they are able to detect.
The main function of a leak detector is to determine the soundness of a pipeline. Unlike gas detectors that are mainly used as a safety device, leak detectors can be used with non-volatile, non-combustible, and non-inflammatory materials and serve as a cost saving measure to prevent product losses.
While gas detectors monitor the air of a location for the concentrations of gases, leak detectors monitor the physical properties of a pipeline and the stability of a pipeline. In many ways, they are more oriented toward the physical and mechanical aspects of a project rather than the purity of the air and oxygen.
As with gas detectors, leak detectors come in a wide variety of shapes and forms with some versions being portable and application specific while other leak detectors are automated detection systems. The choice of the type of leak detector is dependent on the types of leaks, the speed of the flow, and the potential leak rate, which is dependent on the pressure inside the line and outside the line.
The obvious crossover between gas detectors and leak detectors is when a leak occurs, since the concentration of a toxic or flammable gas will rise, altering the oxygen in an area, which will activate a gas detector to sound an alarm. The regular use of leak detectors can prevent leaks of hazardous materials
Chapter 6: How to Select and Layout Sensor Systems
In modern manufacturing, the use of gas analyzers, monitors, and detectors is a necessity and requires the use of the right equipment and tools. The safety of workers and employees depends on the air that they breathe being safe and non-toxic. Choosing the proper monitoring devices requires an understanding of the considerations and features that fit the conditions of an environment and location.
Hazards
The initial step in the selection process is defining the types of gases that are present, which can include CO, HCN, HCL, H2, CO2, NH3, ClO2, HCL, and various forms of volatile organic compounds (VOCs). Each of the gases has their own detection requirements and may necessitate the use of detectors that detect multiple gases. In all cases, the monitor and analyzer should be adjustable to comply with the needs of the conditions.
Detector Type
The types of monitors can be single gas or multiple gases with single monitors being smaller and less expensive while multiple monitors have sets of sensors to detect an assortment of gases.
Reliability
Every gas detector and monitor manufacturer works closely with their clients and customers to place the right monitor for a specific location. The reliability and accuracy of their products is essential to their reputation and ensures the protection of their customers. The design of sensors for industrial use focus on various factors that guarantee the performance, reliability, and accuracy of detectors.
Use
Part of the reliability of gas detectors is in regard to their use, which should be low maintenance, self checking, and provide immediate alerts of problems. The highest quality detectors recharge automatically, are self calibrating, and have other features that make them automated and self sufficient. In essence, the combination of special features can make gas detectors a simple plug and play tool.
Emergency Conditions
Any gas detector should be straightforward with a clear and easy to read display and controls. LED lighting makes it easy to read emergency messages such as ventilate, evacuate, or other forms of data. The design and purpose of gas detectors is to avoid human errors during an emergency.
Power Source
The majority of gas analyzers, monitors, and detectors run on line power and have backup batteries in case of power failures. Detectors with docking stations monitor the battery and calibrate the device, supply alerts, and detect malfunctions. All gas detector manufacturers provide various methods for ensuring their gas detecting devices are continuously functional.
Monitoring
Gas detectors provide real time data that is saved in a management system. The data is used to observe patterns to improve operational readiness and prevent incidents. The saved data helps in determining hazardous areas of a site that have the greatest potential for danger.
Durability
Another critical aspect of gas monitors and detectors is their durability, which is a crucial feature in environments that are potentially toxic. Gas detector and monitor manufacturers adhere closely to ATEX and ANSI certification such that they are producing products of the highest quality and integrity that can endure the harshest and most stressful environments.
Certification
Due to the nature of gas detectors and their use, there are strict standards that guide manufacturers in regard to the manufacture of gas detectors. Two prominent agencies that have similar standards are ATEX and ANSI. All manufacturers ensure that their products are up to international and national standards for the security of their customers. The certification of gas analyzers, monitors, and detectors ensures their quality and performance.
Support and Product Followup
All certified gas detector manufacturers provide exceptional service and support due to the nature of the products they sell. In addition, they provide on site instructions for installation and have a hotline for emergency and unusual circumstances. The key to the success of gas detector products is the type of relationship they develop with their customers.
Gas Detector Placement
After completing the selection process, the next step in the use of gas analyzers, monitors, and detectors is proper placement such that the detector can provide the most reliable and critical data. This aspect of the process requires guidance from gas detector manufacturers who have the expertise and background necessary to make the best use of their products. The main reason for relying on the knowledge of manufacturers is the absence of reliable and consistent information regarding the placement of gas detectors.
In recent years, the incorrect placement of gas detectors has led to their failure and limited their effectiveness. This particular factor is why it is essential that gas detector users rely on industry experts to provide them with guidance, directions, and support regarding the positioning and placement of gas detectors and the required number.
Elements of a successful gas detection system:
Chemicals of Concern
During the gas detector selection process, the types of chemicals to be monitored and measured have been clearly defined and matched with appropriate gas detecting devices. The placement of gas detectors should correlate with the toxic or combustibility of the chemicals being monitored and measured.
Concentration Levels
One of the key factors in the placement process is the concentration of the monitored and measured chemicals. In essence, this aspect of the process can serve as the initial guide and basic platform upon which to build placement and positioning.
Coverage
The two types of coverage are geographic and scenario. The geographic approach places detectors on a uniform grid while the scenario method has a wide range and types of detectors and places detectors according to a dispersion modeling method. Manufacturer guidelines offer the best advice regarding the coverage levels of their products. The primary goal is to place gas detectors in hazard zones, which are identified during the initial assessment.
Hazard Zone Identification
Companies that have invested in gas detectors and monitors are aware of the need for the use of gas detectors. To focus the design of gas detector placement, it is necessary to determine where the potentially hazardous zones are located. The initial phase of the process begins in areas where toxic materials are stored, processed, or generated. This can include storage rooms, boil rooms, confined spaces, and discharge points for valves, pipes, ignition sources, and fittings.
Obstructions
The identification of potential obstructions may require the eyes of an experienced gas detector engineer. As simple as this may sound, all gas detectors have limitations and are partially defined by the area they monitor. Gas detector engineers know the abilities of their products and can discern what obstacles will inhibit the performance of a gas detector.
Environmental Factors
As with any monitoring and measuring device, there are environmental conditions that affect the performance of a gas detector. This aspect of equipment placement is relevant for gas detectors, which can be influenced by temperature, humidity, and airflow. These three factors impact the level of concentration of gases and their movement. Detectors need to be installed in areas where these three environmental factors are stable to ensure the accuracy of the readings and measurements of a gas detector.
Mounting Height
The types of hazardous materials dictate the placement height of gas monitoring and analyzing devices. Higher density gases, like gasoline and propane, are heavier and require detectors located close to the floor. Lighter gases, such as hydrogen and methane, need detectors placed close to the ceiling.
Reference guide for gas detector placement:
Floor Level Placement
Carbon dioxide
Diesel fuel,
Methanol
Refrigerants
Benzene
Breathing Zone - Four to Six Feet from the Floor
Carbon monoxide
Hydrogen Sulfide
Chlorine, Hydrogen Chloride
Formaldehyde
Ammonia
Sulfur Dioxide
Nitric Oxide
Ceiling Level
Hydrogen
Methane
Chapter 7: Gas Detection System Maintenance
The basic function of all gas detection systems is the safety of workers that perform their duties in potentially dangerous and hazardous areas. Under such conditions, hazards are always a concern due to the presence of toxic and harmful gases. The careful placement of a gas detection system ensures that employees will be protected from any negative effects. An essential part of the success of a gas detection system is regular preventative maintenance, which helps avoid system failures.
Reasons for Regular Maintenance
Reliability - Scheduled monitoring of a gas detection system guarantees that the system will function when required.
Accuracy - The major function of a gas detection system is to provide data and accurate readings. Regular maintenance ensures proper readings, helps avoid false alarms, and prevents the implementation of unnecessary safety measures.
Safety - The most critical aspect of a gas detection system is the safety of personnel that could be endangered by a malfunctioning system. Ongoing and scheduled maintenance is an insurance measure that protects workers and keeps a gas detection system working properly.
Cost - Failures of gas detection systems can lead to higher costs in several forms, a factor that all companies wish to avoid. A well designed schedule that regularly assesses the performance of a gas detection system is a necessary measure for the prevention of unwanted and unnecessary costs.
Steps to Gas Detector Maintenance
Physical - A physical inspection of gas detectors includes examining detectors for wear, tampering, damage, cracks, loose screws, loose wires, and the build up of debris, dust, or dirt.
Logs and Record Keeping - As with all forms of device maintenance, it is important to keep a log of any findings from observing a gas detector. This can include adjustments, recommendations, and discrepancies. In addition, the times and dates of inspection is essential since, if there is a problem, it will indicate the amount of time from the last inspection to any malfunction.
Factors Determining the Number of Inspections
Type of gas detector - portable or fixed
Type of sensors
Required accuracy
Gas detector’s recommendations
Dangers and potential damage from environmental conditions
Bump testing
Battery Testing - All forms of gas detector systems have battery backups that have to be regularly checked such that they are capable of providing power if the power goes out.
Software - Of the various aspects of gas detectors, the easiest to maintain is the software since manufacturers provide regular updates and guidance.
Collaboration - A common practice in modern industrial management is the collaboration between users and departments. Such activities prevent misunderstandings and ensure the safety of the work environment. This is especially true in conditions that require the use of gas detector systems.
Calibration - The process of calibration involves the adjustment of the sensors of a gas detector to check if the sensors can detect the concentration and presence of gases, a process that includes exposing the sensors to the gas they are to detect. The registered readings of the sensors are compared to known values and collected data. Inaccuracies require the adjustment of the sensors.
Bump Testing - Bump testing is a functional test that examines whether gas detector sensors respond to its target gas and has alarm functionality. A bump test is performed like calibration in that it exposes the sensors of a gas detector to the gases it is supposed to detect. Unlike a calibration test, the purpose of a bump test is to determine the functionality of a gas detector and not its accuracy. Manufacturers recommend the performance of a bump test on gas detector systems every day.
Chapter 8: Types Gas Detectors by Types of gases
Much like the types of gas detectors, there is a long list of gases that gas detectors monitor. There are three general categories of gases that gas detectors monitor and detect, which are combustible, toxic, and volatile organic compounds (VOCs). Different types of gas sensors react to different gases such that gas detectors can detect a specific type of gas.
Oxygen Detector
Anoxia, the absence of oxygen or an excess of oxygen, is a dangerous problem that can be created by situations that appear to be harmless but produce oxygen depletion or concentration conditions. Oxygen detectors are an essential tool that is used to prevent injuries when there is the potential of varying levels of oxygen where levels can be greater than 23.5%, which can be toxic and a fire hazard. They are normally used when workers are in a confined or enclosed space.
Carbon Dioxide (CO₂) Gas Detector
Carbon dioxide is one of the prime reasons to use gas detectors since carbon dioxide is a deadly odorless and colorless gas that can only be detected by a gas detector. There are several work environments where carbon dioxide can be present and include construction sites, breweries, farming, machine shops, and biofuel production.
Carbon Monoxide (CO) Gas Detector
As with carbon dioxide, carbon monoxide is a very dangerous and deadly gas. When there is too much carbon monoxide in the air, the body replaces red blood cells with carbon monoxide, which leads to tissue damage and death. Like carbon dioxide, it is an odorless and colorless gas that can only be detected by a gas detector. The gas is especially dangerous in enclosed spaces with limited air. There are innumerable areas where high concentrations of carbon monoxide can be found.
Chlorine (Cl₂) Gas Detector
Chlorine gas is a highly toxic gas that causes vomiting, coughing, headaches, chest pain, stomach pain, and corneal burning. Continued exposure to chlorine gas can lead to several severe respiratory illnesses. The gas is prevalent in the pharmaceutical industry, food production, pulp and paper production, and wastewater treatment. It is found in more concentrated forms in plastics, pesticide, gasoline additive, and brake fluid processing.
Hydrogen (H₂) Gas Detector
Oil refineries depend on hydrogen for the processing of crude oil and the removal of contaminants. It is stored in a liquid form or produced on site by electrolysis. Hydrogen gas is non-toxic gas that is highly flammable. High concentrations of it will replace oxygen in confined spaces.
Methane (CH₄) Gas Detector
Methane is the main component of natural gas and is used as fuel to produce heat. It is a highly flammable gas that requires very close monitoring since it displaces oxygen very rapidly. The combustion of methane helps dry, dehumidify, melt, and sanitize products.
Nitric Oxide (NO) Gas Detector
Nitric oxide is a nonflammable, toxic, oxidizing gas that has a very sweet sharp smell. It is a byproduct of the burning of fossil fuels and is released when nitric acid comes in contact with metals. Nitric oxide is produced by the oxidation of nitrogenous materials and is used to produce nitric acid. It is one of the gases that is typically monitored by a multi-gas gas detector.
Nitrogen Dioxide (NO₂) Gas Detector
Nitrogen dioxide is produced by the burning of hydrocarbons and comes from internal combustion engines and thermal power plants. When inhaled, it causes a buildup of fluids in the lungs and severe shortness of breath. Nitrogen dioxide is commonly found at petroleum refineries and coal powered power plants.
Sulfur Dioxide (SO₂) Gas Detector
Sulfur dioxide is a colorless toxic gas that has a very strong odor and is used for the production of sulfuric acid for chemical processing and petroleum refining. The combustion of coal and petroleum produces sulfur dioxide. It is crucial that gas detectors be used to detect the presence of this very dangerous gas.
The small sampling of gases listed here is a representation of the many gases that gas detectors can monitor. From handheld detectors to complex gas detector systems, gas detectors are an essential tool for the protection and safety of workers. Gas detectors can be programmed and configured to detect any form of gas and come in different designs to meet every industrial requirement.
Conclusion
A critical part of a worker and environmental safety system is a gas detector that sounds an alarm that an unsafe concentration of gas is present.
Gas detectors are widely used to detect combustible gases, flammable materials, toxic gases, and the depletion of oxygen in an area.
Gas detectors are classified according to their detection method, which can be semiconductors, oxidation, catalytic, photoionization, or infrared light.
Portable gas detectors are handheld gas detectors that are designed for personnel use. They monitor the concentration of toxic gases around an individual and are battery operated with some versions being disposable while other portable gas detectors are rechargeable.
Fixed gas detectors are normally part of a detection system that includes a controller, several open path and point gas detectors, and a warning system.
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