Fixed gas detectors are used to protect a facility in a single area and act as an early warning indicator of high gas levels or leaks.
These detectors are designed to alert workers of the potential danger of poisoning by toxic gas exposure, asphyxiation due to lack of oxygen, or explosion caused by combustible gases.
What is a fixed gas detector?
A fixed gas detector is a safeguarding system that constantly monitors a location due to the excess levels of gases.
Unlike portable detectors, fixed detection devices make it possible to secure an entire area 24 hours a day.
They can also be connected to a detection system, which displays the gas concentration in numerical value, and then triggers the servo-controls in the event of an abnormal value.
Is a fixed gas detection system necessary?
Yes, a Fixed gas detection system is necessary as it is often required to protect facilities by the insurance companies that underwrite them and even by some standard electric codes.
It can alert potential danger before it occurs
Fixed detectors are used to detect an abnormal or dangerous presence of gas in a specific area and to warn the user in the event of potential hazards.
Equipped with sensors (called cells), they can measure the concentration of one or more types of gas, depending on the model.
It will protect your facilities 24/7
Unlike portable detectors, fixed detection devices make it possible to secure an entire area 24 hours a day.
They can also be connected to a detection system, which displays the gas concentration in numerical value, and then triggers the servo-controls in the event of an abnormal value.
It can be connected with other security systems
Fixed gas detectors can easily be connected with other security systems like fire suppression systems, smoke detection systems, etc, to one control panel and help to simplify the control of your facility.
It is required by law
OSHA, NIOSH, NFPA, and other government agencies will want you to have some kind of a fixed gas detection system in certain facilities
What are the Components of a Fixed Gas Detection System?
A fixed gas detection system consists of 3 parts: the sensor, transmitter, and controller.
The sensor
The sensor is the actual device that senses the gas. Many sensors, such as catalytic beads, infrared, and electrochemical, are used in gas detection.
Sensors typically last 2 to 4 years but can last longer or shorter depending on the application’s nature.
Solid-state and Infrared sensors typically last much longer, and it is not uncommon for them to last 5 to 10 years or more.
Most fixed sensors can work as standalone units, but it is better to connect them to a transmitter and a controller if you want to integrate them with other systems.
The Transmitter
Most sensors require a transmitter to amplify the signal and convert the gas sensor signals into a standardized output, such as 4-20 mA, Modbus, and HART, for transmitting the signal to a controller.
The transmitter is usually close to the sensor, and zero and span adjustments must be done at the transmitter.
Most transmitters are operated from 24 VDC and utilize 2 or 3 wires. In general, even if a sensor can be used without a transmitter, the use of a transmitter is often preferred for distances over 300’ to 500’ to simplify the calibration effort.
In general, even if a sensor can be used without a transmitter, a transmitter is often preferred for distances of 300’ to 500’ to simplify the calibration effort.
The Controller
The controller is the device that receives and interprets the signals from the sensors and sensors/transmitters.
The controller typically provides a readout of the gas concentration, audible and visual alarms for dangerous gas levels, and generally alarm relays for activating an external alarm or other action.
In some applications, it is preferred to send the transmitter signal (such as 4-20 mA) directly into a
PLC (Programmable Logic Controller) or other similar control devices. In this case, the PLC activates the alarm conditions and relays, and a “Gas Detection” controller is not necessary.
What is the best mounting height for fixed gas detectors?
This is one of the questions I get most of the time. In my experience, the mounting height at which a fixed sensor should be mounted depends on the density of the gas it monitors relative to the air.
Heavier than air
Gases that are heavier than air will tend to sink to the floor and concentrate there, my recommendation for the sensors that detect these types of gases is to mount them 1 to 3 feet from the floor.
Lighter than air
Gases like Hydrogen and Methane are lighter than air, which means the gases will rise and concentrate near the roof.
If you have a fixed gas detector to measure any gas which is lighter than air you need to mount the sensors 1 to 3 feet from the ceiling.
Similar to air
Gases that have a relative density similar to air will be floating in the air near the breathing zone. Mount sensors in the breathing zone, which is 4–6 feet above the floor.
If you do not know if the gas in question is heavier, lighter, or similar to air, you can google the relative density of that gas, if it is above 1, means it is heavier than air, if it is less than 1 means it is lighter than air and if it is about 1, means it is the same as air.
Tips for mounting fixed gas detectors
- Place sensors near the source of the gas, like piping or a compressor.
- Mount sensors in areas with good air circulation, but not in areas with rapidly moving air.
- Avoid mounting sensors near room entrances, fresh air intake vents, or vehicle/generator exhaust points.
- Mount sensors upright on a vertical surface, like a wall, beam, or column.
- Consider how accessible the sensor is for calibration and maintenance.
- If you have a separate display from the sensor, mount it where it’s easy to read
FAQ: Fixed Gas Detection System
What is the difference between fixed and portable gas detectors?
Fixed Gas Detectors: Ideal for continuously monitoring specific areas or zones within facilities where gas hazards are present.
Portable Gas Detectors: Suitable for applications requiring mobility, such as confined space entry, leak detection, maintenance activities, or outdoor monitoring.
Read about portable gas detectors here.
What are the two types of gas detection systems?
Gas detectors come packaged into two main form factors: portable devices and fixed gas detectors.
Final words
That is it. Those are the three main components of a fixed gas detection system. Thank you for reading.