There are two main types of gas detection equipment: fixed detectors and portable devices. Each is designed to monitor a specific kind of atmosphere.
Portable monitors are worn or carried by employees and are ideal for confined space operations or to assess manure gas in a landfill. They detect multiple hazards at once, including IDLH (Immediately Dangerous to Life and Health) and LEL (Lower Explosive Limit) gases.
Fixed Detectors
When most people think of fixed gas detection systems, they imagine a large system with dozens of transmitters in expensive explosion-proof housings, wired together using cabling installed in stainless steel conduit and connected to an expensive PLC or programmable logic controller (PLC) located somewhere in the plant. This is one type of fixed gas detection system, but there are many others that are much simpler and less costly.
The main advantage of a fixed system is that it continuously monitors the area and alerts people to any gases in the air that could be hazardous. This can reduce workers’ time in potentially dangerous environments, create a safer workplace environment, and even satisfy insurance policy requirements.
A fixed system can also be linked to building management systems, allowing outputs to activate visual and audible alarms, close electronic valves, and open/close ventilation fans. This can be useful in a wide range of settings, from oil refineries and manufacturing plants to industrial sumps and ventilation shafts.
There are a few things to consider when choosing the location of fixed sensors. Firstly, they should be placed in areas where a leak is most likely to occur. This can include confined spaces, equipment or pump sumps, weld joints, and flanges. In addition, it is important to consider the density of the gas being detected. For example, CO2 sensors should be positioned downwind of the leak source as the gas has a lower molecular weight and therefore sinks in the air.
Finally, it is important to remember that fixed sensors will only detect gases that are in direct contact with them. This means that they will not be able to cover the entirety of any leak potential in an area, as it is likely that people will move about the space and interact with the gases. For this reason, it is often best to combine a fixed gas detection system with portable gas detectors in order to provide the fullest possible protection.
Portable Detectors
Designed to be worn on the body, portable detectors are usually only a few ounces and clip to a person’s collar, lapel, or bag. They are battery-operated and can be set to trigger an audible, vibrating, and flashing alarm that enables workers to hear and see the warning in noisy or low-visibility environments. They can also be used to test for gases like hydrogen sulfide (H2S), which damages the lungs and does not have a distinctive odor at normal concentrations but can damage olfactory sensors at high levels.
The sensors in a portable gas monitor use metal oxide semiconductors to detect the presence of toxic and/or explosive gases by measuring their change in electrical resistance. The change in resistance is caused by the gases interacting with the sensor, causing it to heat up. The heater is powered by a battery and it’s the difference in voltage generated by this process that is measured by the sensor to identify the harmful gases.
Portable detectors can be either single or multi-gas and come with a range of features, including a clear LCD display screen that shows data in real-time, logging capability, and an audible and visual alarm system for alerting the user to dangerous levels. Some portable monitors can even connect to a mobile app that uploads monitoring data to the cloud in real time, making it available for analytics and insights.
When it comes to choosing a portable gas detector, it’s important to consider the working conditions and activities that will be undertaken. Look for monitors that have been rated to operate in harsh environments and have passed rigorous atmospheric and physical tests. They should be able to cope with drops, sprays, and submersion. They should also have a long battery life and easy-to-print tamper-proof calibration certificates.
Some fixed detectors can be hardwired to a larger system to provide alerts for specific hazards and have the ability to trigger relays that will shut off equipment or activate third-party systems like ventilation or fire panels. They should also be ATEX classified and approved for use in a hazardous area and carry a DSEAR report indicating their suitability for the specific application.
Transmitters
A transmitter converts a non-standard electrical output signal from the sensor into a standard electric current or voltage signal that can be easily read and monitored. The microprocessor inside a transmitter also processes the sensor’s data and provides convenient, automated functions such as self-testing, error correction, and compensation. This information can then be used to control the instrument’s output. A transmitter also serves as a communication link between the sensor and other devices in the system.
There are several different types of sensors used in gas detection equipment. The most common are catalytic diffusion sensors for combustible gases. These sensors consist of two beads – one inert and the other coated with a chemical catalyst. When exposed to a combustible gas, the catalyst heats up, and this is detected by the inert bead. These sensors are typically calibrated for a single gas and are very durable.
Electrochemical sensors are also used and work by measuring the chemical potential difference (CMD) between a pair of electrodes. This allows for the direct measurement of gases such as carbon monoxide, hydrogen sulfide, and manure gas which are generated during decomposition in confined space manure storage tanks. These sensors are very easy to use and provide immediate results with a digital display.
Other types of sensors include flammable gas detectors that warn workers when combustible gases reach safety thresholds that could result in an explosion. These detectors are used in the petroleum, manufacturing, and chemical industries where explosive gases may be present. These are typically calibrated for LEL – lower explosive limit – which is the minimum concentration of a gas in the air above which an explosion will occur.
Portable gas detectors have the ability to detect a wide range of toxic gases, including oxygen depletion, which can lead to drowsiness or unconsciousness, and carbon monoxide, which is odorless and colorless. These devices alert workers through a loud audible, and vibrating alarm. They are battery-operated and can be carried or worn unobtrusively.
All detectors must be properly maintained to ensure their operation and effectiveness. This includes routine calibration and inspection of the sensor and other parts. In hazardous environments, look for a detector with an intrinsic safety rating that has been tested and approved by a recognized third-party approval agency such as UL, CENELEC, or FM. This certification indicates that the detector is able to protect itself from ignition by gases that may come into contact with the sensor or its wiring. A built-in flame arrestor provides this protection, which acts as an effective barrier to prevent gases from entering the device.
Controllers
There are many options when it comes to choosing the right gas detection equipment. Each worksite presents different safety risks, and each type of detector is suited to particular environments. A basic overview of the function and features of each option will help you determine which is the best choice for your specific situation.
The function of a gas detector can be broken down into three parts: monitoring combustible or toxic gases, the user interface that tells people of danger and any actions they need to take, and the power management system that keeps everything charged up and working. Detectors are at the heart of every gas detection system and can be categorized as portable or fixed.
Fixed detectors are designed to monitor a limited volume around them (typically within a 5M radius). They may be diffusion or pump (aspirated) types; the best choice is application-dependent.
Combustible gas detectors use catalytic diffusion sensors, essentially two beads, one inert and the other coated with a chemical catalyst. The catalyst heats up as it encounters combustible gases and causes a change in electrical resistance. The sensor then measures this variation in electrical resistance and compares it to a threshold level. If the threshold is reached, an output pin signals that a hazardous level has been detected, and an alarm is activated.
Toxic gas detectors also use a similar technology to detect hazardous chemicals in the air. They do this by sampling the air for the presence of known toxic substances and alerting people nearby if they’re at risk. Toxicity detectors can identify a range of toxic gases, including carbon monoxide, a common byproduct of incomplete combustion.
A final category of gas detectors is the gas leakage sensor, which works to identify dangerous gases by sound. It can be used in a variety of applications and environments, such as painting, fumigation, fuel filling, construction, excavation of contaminated soils, landfill operations, entering confined spaces, and more. Gas leakage sensors typically work with an audible alarm to warn people of a hazardous gas build-up and release.