A 4-gas monitor detects oxygen (O2), carbon monoxide (CO), hydrogen sulphide (H2S), and combustible gases, often measured as Lower Explosive Limit (LEL). For anyone working near gas or potentially hazardous areas, knowing how to use a 4-gas monitor may save your life.
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A 4-gas monitor is a portable, battery-powered device that detects four main gases: Oxygen (O2), Carbon Monoxide (CO), Hydrogen Sulphide (H2S), and Combustible Gases (LEL). It gives real-time gas level read-outs with alarms to immediately warn when there is an unsafe level of gas in an area. They are essential for anyone who works within confined spaces, or carries out gas line installations and leak detection.
A 4-gas monitor detects when unsafe levels of the following gases are detectable:
To breathe safely, air needs an oxygen level of at least 19.5%. Anything below this is a hazard and can lead to symptoms such as dizziness, confusion, or even loss of consciousness.
Carbon monoxide is a toxic, odourless, potentially deathly and colourless gas, often referred to as a "silent killer." It is produced by combustion engines, or by fuel-powered tools, heaters, or other equipment operating in poorly ventilated areas.
Hydrogen sulphide is a highly toxic gas commonly associated with sewer systems or the decomposition of organic materials. Chances are, you'd be able to smell it — at first. However, at high concentrations, it can numb the sense of smell, making it even more dangerous as workers may not detect it.
Combustible gases, like methane, propane, and butane, pose a significant risk of fire or explosion if their concentrations reach the Lower Explosive Limit (LEL). They can build up undetected in poorly ventilated areas.
Properly using a 4-gas monitor is particularly critical for your safety during:
Although the exact way to operate a 4-gas monitor will change per unit, follow these basic steps to ensure yours is working properly:
The following table outlines the safe levels for gases commonly monitored by a 4-gas detector. These levels are defined by organisations like OSHA (Occupational Safety and Health Administration), NIOSH (National Institute for Occupational Safety and Health), and ACGIH (American Conference of Governmental Industrial Hygienists).
| Gas | Low Alarm | High Alarm | TWA | STEL |
|---|---|---|---|---|
| Oxygen (O2) | 19.5% vol | 23.5% vol | N/A | N/A |
| Carbon Monoxide (CO) | 35 ppm | 70 ppm | 35 ppm | 200 ppm |
| Carbon Dioxide (CO2) | 0.5% vol | 1.0% vol | 0.5% vol | 3.0% vol |
| Ammonia (NH3) | 25 ppm | 50 ppm | 25 ppm | 35 ppm |
| Methane (CH4) | 1.0% vol | 1.5% vol | N/A | N/A |
| Hydrogen Sulfide (H2S) | 10 ppm | 20 ppm | 10 ppm | 15 ppm |
| Sulfur Dioxide (SO2) | 2.0 ppm | 4.0 ppm | 2.0 ppm | 5.0 ppm |
| Nitrogen Dioxide (NO2) | 3.0 ppm | 6.0 ppm | 3.0 ppm | 5.0 ppm |
| Nitric Oxide (NO) | 25 ppm | 50 ppm | 25 ppm | 25 ppm |
Explain maintenance tips to keep the monitor reliable:
This detector features rapid-response MSA XCell® sensors and offers a 4-year warranty. It monitors combustible gases, oxygen, carbon monoxide, and hydrogen sulfide. The device is known for its durability, surviving drops from up to 25 feet, and operates in temperatures ranging from -40°F to +140°F (-40°C to +60°C). It also provides real-time incident awareness when paired with the MSA ALTAIR Connect app.
This detector has an icon-based interface in a serviceable package, monitoring hydrogen sulphide, carbon monoxide, oxygen, and combustible gases. It's battery runtime lasts up to two months on a 4.5-hour charge and utilises a low-power infrared LEL sensor immune to silicone poisoning. The device is lightweight, features one-button operation, and is compatible with the IntelliDoX instrument management system and Honeywell Safety Suite.
This smaller detector still reliably measures combustible gases and vapours, as well as oxygen, carbon monoxide, hydrogen sulphide, nitrogen dioxide, and sulphur dioxide. It features durable sensors and offers reliable measuring technology.
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