A gas detector is a device that detects the presence of gases in an area, which is often as part
of a safety system. The equipment is used to detect a gas leak or other emissions and can
interface with a control system so a process can be automatically shut down.
A gas detector can sound an alarm to operators in the area where the leak is occurring,
giving them the opportunity to leave. This type of device is important in industries and homes
where gas is used, because there are many gases that can be harmful to humans or animals.

This type of device is used in industry and can be found in locations like; oil rigs, to monitor
manufacture processes etc. They are used in detection of the following;
· Combustible
· Flammable
· Toxic gases
· Oxygen Dpletion

What Is Gas Leaks?
Gas leak detection is the process of finding potentially hazardous gas leaks by sensors. These sensors usually employ an audible alarm to alert people when a dangerous gas has been
detected. Exposure to toxic gases can also occur in operations such as painting, fumigation, fuel
filling, construction, excavation of contaminated soils, landfill operations, entering confined
spaces, etc.

Gas detectors can be classified according to the operation mechanism (semiconductors, oxidation, catalytic, photoionization, infrared, etc.). Gas detectors come packaged into two main form factors: Portable devices and fixed gas detectors. Portable detectors are used to monitor the atmosphere around personnel and are either hand-held or worn on clothing or on a belt/harness. These gas detectors are usually battery operated. They transmit warnings via audible and visible signals, such as alarms and flashing lights, when dangerous levels of gas vapors are detected.

Fixed type gas detectors may be used for detection of one or more gas types. Fixed type
detectors are generally mounted near the process area of a plant or control room, or an area to be protected, such as a residential bedroom. Generally, industrial sensors are installed on fixed
type mild steel structures and a cable connects the detectors to a SCADA system for continuous
monitoring. A tripping interlock can be activated for an emergency situation.

Electrochemical Gas Sensor
Electrochemical gas detectors work by allowing gases to diffuse through a porous membrane to an electrode where it is either chemically oxidized or reduced. Electrochemical gas detectors are used in a wide variety of environments such as refineries, gas turbines, chemical plants,
underground gas storage facilities, and more.

Catalytic bead Sensor
Catalytic bead sensors are commonly used to measure combustible gases that present an
explosion hazard when concentrations are between the lower explosion limit and upper
explosion limit. The measureable concentration ranges are typically from a few hundred ppm to a
few volume percent. Such sensors are inexpensive and robust. Photoionization Detector
Photoionization detectors (PIDs) use a highphoton-energy UV lamp to ionize chemicals in the
sampled gas. If the compound has ionization nergy below that of the lamp photons, an electron
will be ejected, and the resulting current is proportional to the concentration of the compound.
A broad range of compounds can be detected at levels ranging from a few ppb to several thousand ppm.

Detectable compound classes in order of decreasing sensitivity include: aromatics and alkyl iodides; olefins, sulfur compounds, amines,ketones, ethers, alkyl bromides and silicate esters;
organic esters, alcohols, aldehydes and alkanes;H2S, NH3, PH3 and organic acids. Infrared Point Sensor Infrared (IR) point sensors use radiation passing through a known volume of gas; energy from the sensor beam is absorbed at certain wavelengths, depending on the properties of the specific gas. This type of sensor is advantageous because it does not have to be placed into the gas to detect it and can be used for remote sensing. Infrared point sensors can be used to detect hydrocarbons and other infrared active gases such as water vapor and carbon dioxide.
Infrared sensors are commonly found in wastewater treatment facilities, refineries, gas turbines,
chemical plants, and other facilities where flammable gases are present and the possibility of
an explosion exists. The remote sensing capability allows large volumes of space to be monitored. Calibration of Gas Detectors All gas detectors must be calibrated on a schedule. Of the two form factors of gas detectors, portables must be calibrated more frequently due
to the regular changes in environment they experience. A typical calibration schedule for a fixed system may be quarterly, bi-annually or even annually with more robust units A typical calibration schedule for a portable gas detector is a daily “bump test” accompanied by a monthly calibration. Almost every portable gas detector requires a specific calibration gas which is available from the manufacturer.

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