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What is a 4 Gas Monitor?

4 gas monitor

Gas detectors have been around since the 1800s and became a concern after the effects of harmful gases on human health was discovered. Before modern-day gas sensors, early detection relied on less precise technologies. Through the 18th and early 19th centuries, gas detectors would be used to detect the presence of gases like methane in underground coal mines. (see history of "canary in the coal mines").

Today, the cost and performance of gas sensor technology has drastically improved, allowing the ability for more accurate, robust, and precise detection. Now, you can find gas detectors incorporated into a much wider range of systems and applications such as demand-control ventilation, engine emissions, indoor air quality, beverage and hospitality, indoor agriculture, and more.

If you need to monitor several gases at the same time for work, you need a 4-gas monitor. These handheld tools can measure one or more gas concentration in real time and are commonly used to protect workers in enclosed spaces.

What is a multi gas detector? 

A 4-gas monitor is a gas detector that is intended to detect multiple gas concentrations at the same time. It is used most commonly as a personal gas device in industries such as pharmaceutical, indoor agriculture, fire suppression testing, sanitation, and industrial processes. Multi gas detectors typically also use sensors to detect the presence of gases such as carbon monoxide (CO), hydrogen sulfide (H2S), oxygen (O2), and combustible gases such as methane (CH4).

One example, is the Multi-Gas Sampling Data Logger. This device provides analysis for inert gases such as carbon dioxide (CO2), oxygen (O2), methane (CH4) carbon monoxide (CO) and more. Like many other multi gas detectors, this device is capable of detecting four or more gases simultaneously. The detectors are also designed to provide indication should levels not meet the specific application thresholds. See here for gas detection system requirements and alarm level setpoints

This device also uses a lithium ion rechargeable battery with long battery life, an LCD display screen to show gas levels in real-time, graphed data, data logging, and audible alarm if one of the gas levels is dangerous.

Other terms that are used to describe a multi gas monitor include 4 gas meter, 4-gas detector, multi-gas monitor, multi-gas detector, or 4-gas sniffer.

While many customers find both 4 gas monitors and portable gas detectors, critical across applications, 4 gas monitors work differently and are more robust to gain constant monitoring across several gases within one device. These devices are commonly found beneficial in areas such as oil and gas, pharmaceutical, fire suppression, and chemical manufacturing. Some models of multi gas detectors can also hold data logging capabilities, which can be even more helpful when tracking gas levels over time or for regulatory purposes.

How does a 4 gas monitor work?

4 gas or “multi gas” monitors are basically a hand-held computer with single task: read the gas sensor data and make it available either on screen or saved to a log file. The secondary task is to sound an alarm if one of the gas levels are too high. Because of these limited requirements, they have a smaller screen and far fewer buttons than a PC keyboard which makes them easier to use in the field.

Open a multi gas monitor and you'll find:

  • A sensor for each type of gas
  • A printed computer board filled with IC chips
  • A display screen
  • Included li-ion rechargeable batteries

The challenge when designing a 4 gas monitor is that everything must be designed as small as possible to make them portable, and the low-power sensors must be selected to improve battery life. For these reasons multi gas monitors tend to be more expensive than their desktop counterparts which can use older or more power-hungry components.

What makes a portable, multi gas monitor a useful solution is that it combines all these features and benefits in a hand-held design.

Pros and Cons of using a 4-gas monitor:


  • Ensure maximum safety and protection from several gases
  • Easily detect hazardous gases in one device
  • Audible/Visual instant indication should hazardous levels be present
  • Portable, hand-held and battery operated options so you can monitor quickly from place to place
  • Data logging capabilities to monitor concentrations over time (portable options)


  • Routine calibration and testing is required for accurate performance
  • Some gas detectors only last 2-5 years dependent upon the gas sensor
  • No ability to monitor every hazardous gas in one platform



What does a 4 Gas Monitor detect?

Aside from monitoring critical elements like temperature or humidity, most multi gas detectors are designed to detect gases such as:

  • Oxygen (O2)
  • Carbon Monoxide (CO)
  • Carbon Dioxide (CO2)
  • Ammonia (NH3)
  • Particulate Matter (PM)
  • Hydrogen Sulfide (H2S)
  • Methane (CH4)
  • Combustible gases (LEL) like methane and propane

Other gases that 4 gas monitors can include but are not as common are:  acetone, industrial solvents, alcohol, lacquer, thinners, benzene, butane, naphtha, ethylene oxide, natural gas, gasoline, propane, halon, refrigerants, hydrogen sulfide, and toluene.

    Basically, if there is a sensor that can detect a gas, there is a 4 gas detector available in the market that includes it. Plus, what makes a portable, 4 gas detector a useful solution is that it combines all of these features and benefits in a hand-held design.  

    Why use a Gas Detector?

    Depending on your application, the primary benefit of using a gas detector is essential when discussing safety. For example, one detector can be used to prevent risks linked to low oxygen atmosphere, safeguard against CO2 exposure, monitor LEL (lower explosion limits) or combustible gases, and remove threats from potentially lethal environments.

    The gas sensor at the core of any gas detector is what helps prevent the high risk of gas exposure and affects any casualties within and outside the premises. These gas sensors help detect the concentrations of the gases present in the atmosphere to avoid hazards from occurring, human exposure, and mitigate any fatalities.

    How to Calibrate a Multi Gas Detector?

    Calibration is one of the most necessary services for any multi gas detector or application. Though you should always utilize the gas detector manufacturer for this service, you can carry on this task yourself with the correct instructions. Further, you should be doing calibration of your device annually to ensure optimal performance and increase your gas detector life span. 

    A typical calibration involves adjusting the device to ensure that it is providing accurate readings for the gases being detected. The exact calibration procedure will depend upon the specific make and model of the detector, but here are a few general tips:

    1. Consult the user manual: The first step is to consult the user manual for your specific multi-gas detector. The manual will provide specific instructions on how to calibrate the device, as well as any tools or equipment needed.

    2. Select calibration gas: Calibration gas is used to test the accuracy of the detector's sensors. Choose the appropriate calibration gas based on the gases being detected by the device.

    3. Prepare the calibration gas: The calibration gas must be prepared according to the manufacturer's instructions. This may involve attaching a regulator to the calibration gas cylinder and connecting it to the detector using tubing.

    4. Turn on the detector: Turn on the multi-gas detector and let it warm up for the recommended amount of time.

    5. Initiate calibration mode: Most multi-gas detectors have a calibration mode that can be accessed through the device's menu or buttons. Follow the manufacturer's instructions for entering calibration mode.

    6. Expose the sensors to calibration gas: Once in calibration mode, expose the sensors to the calibration gas. The gas concentration should be within the range specified in the user manual.

    7. Adjust the device: The detector should display a reading that matches the known concentration of the calibration gas. If the reading is not accurate, adjust the device according to the manufacturer's instructions.

    8. Complete the calibration: Once the readings are accurate, complete the calibration according to the manufacturer's instructions. This may involve pressing a button or navigating through menus to exit calibration mode.

    9. Confirm accuracy: After calibration is complete, confirm that the device is providing accurate readings by exposing it to fresh air and verifying that it shows a zero reading for all gases.

    At CO2Meter, we offer a number of educational resources and guides to make calibrating your device easier and increase your detectors longevity in the field.

    It is always recommended that anyone working near hazardous gases consult the OSHA guidelines for calibration requirements and procedures.

    What industries use 4 gas monitors?

    Indoor Air Quality (IAQ)

    Because indoor air quality environments need to monitor for CO, CO2, and O2 - the combination found in the CM-505: Carbon Dioxide, Carbon Monoxide and Oxygen Handheld Detector is ideal. Because of features like the large LCD display, audible alarms, data logging capabilities, and multi-gas functionality, the GasLab Plus® serves as "go-to" gas detection solution for many customers. Especially so, during the pandemic in providing individuals with proper monitoring to ensure air filtration and create a healthier living space.

    Overall, indoor enclosed spaces such as homes, offices, classrooms, and gymnasiums are always looking to provide energy efficiency and reduce wear and tear on HVAC systems. The added benefit of installing a CO2 monitor specifically can improve cognitive abilities, promote energy efficiency, and reduce airborne illnesses. One fixed gas detector commonly sought after is the CO2, Temp, and RH Indoor Air Quality Monitor.

    See our Carbon Dioxide (CO2) classification guide for indoor air recommended levels.

    Indoor Agriculture

    For many indoor growers, farmers, and cultivators using gas detection in their field is critical to further maximize plant yields and increase crop productivity. Carbon Dioxide is the key to furthering crop yields and our Dual Indoor CO2 Grow Controller is often the preferred gas detector solution for those looking into further optimizing their grow space. 

    Just as control is an added benefit to indoor growers, gas safety is just as important and this application also utilizes gas safety detectors in order to detect higher than normal CO2 concentrations and warn growers of potential dangers. Equipped with both a main sensor unit and a remote display, a fixed gas safety detector is typically installed in the grow space where the inert gas source point is located.

    Poultry and Livestock

    When it comes to poultry and livestock applications, both Carbon Dioxide (CO2) and Ammonia (NH3) are considered key pollutants. For farmers, being able to gain analysis of higher concentrations in animal barns can provide understanding of the health of animals and the workers. In turn, providing knowledge to better ventilate the space, increase healthier environment for staff, and promote productivity in the livestock.

    In order to better gauge NH3 and CO2 concentrations in indoor environmental conditions such as poultry farms, the (CM-507) Carbon Dioxide (CO2) and Ammonia (NH3) Gas Detector is used.

    Scientific and Medical 

    With the use of many inert gases in incubation and life science environments, technicians require complete analysis of carbon dioxide (CO2) and oxygen (O2) specifically in research processes. Because oxygen is used as an essential component for cell growth combined with carbon dioxide for embryo development, measuring both of these inert gases is critical for controlling pH.

    By using our multi gas sampling data logger researchers are able to maintain the specific environments that are needed for cultures at about 20% O2 and 5-7% CO2. With the explosion of incubation use, especially in fighting diseases like Covid-19, gas detection and analysis will only continue to be an important tool to further advancements.

    Pest Abatement

    This application includes individuals or businesses looking to inject gas into a confined space to drive out or euthanize pests, rodents, bed bugs, roaches, or even prairie dogs.  By driving in large volumes of high concentration CO2 the pests are driven from the space - or they die.  The CM-1000 Multi Gas Sampling Data Logger is utilized to determine the precise high levels of CO2 as well as the depletion of oxygen in the space to maximize the process.

    Over the years, CO2Meter has worked alongside many companies and scenarios where pest abatement or control is vital - such as on commercial aircraft.  With the temporary "mothballing" of commercial aviation fleets due to Covid-19 many fleet maintenance teams are ramping up efforts to service aircraft including pest abatement. Not only can inert gases like carbon dioxide (CO2) be a more cost effective means of euthanasia, the gas can also provide an efficient means of abatement without damaging any of the flight controls during the process.

    Fire Suppression Testing

    For those in fire suppression applications, using a gas detector or multi-gas detector includes the critical component necessary in this field - which is a micropump. This pump is able to simultaneously measure multiple gas concentrations through a single sampling port. To further accommodate customers in need of testing their CO2 fire suppression systems CO2Meter uniquely designs the CM-1000 to NFPA 12  standards which requires testing at low, medium, and high points within the space at specific rates.

    The 100% Carbon Dioxide Sampling Data Logger is the only device manufactured that meet these requirements. In addition, the suppression system must reach and hold specific CO2 concentrations over a given period of time making the 100% model of the multi gas monitor series, a necessity in this environment. 

    Customers wanting to monitor oxygen depletion in the environment may also add a 0-25% oxygen sensor to measure and log this additional data.

    How long does a 4 Gas Monitor last?

    The typical lifespan of any gas detector depends on the type of sensor technology that is used at its core.

    For reference, most electrochemical sensors usually last between 2-3 years, non-dispersive infrared sensors lasts between 5-15 years, and a more exotic gas sensor may last only 12-18 months.

    We typically advise our customers to ensure they are purchasing a gas detector with high quality sensing technology and are getting the device annually serviced/calibrated to ensure consistent and long-lasting performance and operation.

    Here is a helpful chart below that shows each gas sensor and the typical life expectancy:

    Electrochemical   2-3 years
    Non-dispersive Infrared   5-15 years
    Opto chemical   2-7 years
    Catalytic Bead  4-5 years
    UV Flux   2-5 years
    Metal Oxide >10 years

    How often should you calibrate a 4 gas monitor?

    The calibration frequency for a 4 gas monitor, or any gas monitor, depends on several factors including manufacturer recommendations, regulatory requirements, usage conditions, and the specific gas sensors involved.

    It is essential to refer to the manufacturer's guidelines and manuals for the specific gas monitor model you are using, as they will provide the most accurate and reliable information.

    In general, most manufacturers recommend calibrating gas monitors on a regular basis, typically every year. However, certain situations may require more frequent calibration. Here are some factors that may influence the calibration frequency:

    1. Manufacturer Recommendations: Follow the calibration schedule recommended by the manufacturer of your specific 4 gas monitor. The manufacturer's guidelines take into account the sensor technology, performance characteristics, and expected drift over time.

    2. Regulatory Requirements: Depending on the industry or the specific application, there may be regulations or standards in place that dictate the calibration frequency for gas monitors. Compliance with these regulations is important for safety and legal reasons..

    3. Usage Conditions: The calibration frequency may vary based on the conditions in which the gas monitor is used. For example, if the monitor is exposed to harsh or extreme environments, high levels of contaminants, or potential sensor poisoning agents, more frequent calibration may be needed.

    4. Sensor Stability and Drift: Gas sensors can experience drift over time, leading them to stray from their initial calibration. Regular calibration helps to correct any inaccuracies and maintain the accuracy of the gas monitor's readings. Some sensors may require more frequent calibration due to their stability characteristics.

    5. Previous Calibration Results: The results of previous calibrations can provide valuable insights into the stability and performance of the gas monitor. If there have been significant deviations or discrepancies in previous calibrations, it may be necessary to increase the calibration frequency to ensure accurate readings.

    Remember to follow proper calibration procedures as specified by the manufacturer, which typically involve using calibration gases of known concentrations or following specific steps to send the device back to the manufacturer for calibration adjustment.

    It is always recommended to consult the manufacturer's guidelines and seek advice from qualified professionals to determine the appropriate calibration frequency for your specific 4 gas monitor based on the factors mentioned above.

    What are the typical 4 gas meter alarm levels?

    Provided standards exist, all alarm settings are based on the following OSHA PEL, TWA, and STEL settings.

    Oxygen (O2) 19.5% vol 23.5% vol N/A N/A
    Carbon Monoxide (CO) 35 ppma, b
    70 ppmb
    35 ppma 
    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

    What gas detector levels are considered hazardous?

    While various fire codes, government agencies and industry-led associations recommend specific gas exposure safety limits. Below are some examples for each gas as indicated by the proper regulatory standard or association.

    Oxygen (O2) Deficiency


    Recommendation / Requirement

    Occupational Safety and Health (OSHA)

    Air is considered oxygen-deficient below 19.5%

    National Institute for Occupational Safety and Health (NIOSH)

    Air is considered oxygen-deficient below 19.5%

    American Conference of Governmental Industrial Hygienists (ACGIH)
    <18% is minimum partial pressure without need for respiratory protection at normal atmospheric pressure

    Carbon Monoxide (CO) 


    Recommendation / Requirement

    World Health Organization (WHO)

    9 ppm average over 8 hours

    Environmental Protection Agency (EPA)

    9 ppm average over 8 hours

    The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)

    9 ppm average over 8 hours

    National Institute for Occupational Safety and Health (NIOSH)

    35 ppm average over 10 hours

    200 ppm ceiling value

    Occupational Safety and Health (OSHA)

    50 ppm average over 8 hours

    American Conference of Governmental Industrial Hygienists (ACGIH)

    25 ppm average over 8 hours


    Combustibles, Explosives (EX) %LEL (Methane)

    Recommendation / Requirement

    National Institute for Occupational Safety and Health (NIOSH)

    1,000 ppm 8 hour TWA [methane]
    = 2%LEL

    50,000 ppm (5%vol) IDHL Immediately Dangerous To Life or Health [methane100%LEL

    Factory default alarms for LEL are set 20% for low. At Forensics Detectors, alarms are set at 50% for high.


    How do you select a multi gas detector?

    When selecting the right gas detector you should always make sure you are aware of the gases that are commonly used/produced/stored in your industry or environment.

    One common gas detector that CO2Meter often refers customers to is the CM-500 GasLab Plus® lineup of portable gas detectors. These gas detectors are easy to use and offers six user-friendly buttons making operation of the device trouble-free. In addition, this device offers different combinations of (CO2, CO, NH3, O2, and PM) making it diverse across multiple applications and industries.

    For more information on gas detection and to better assist you in choosing the right gas detector, one of our gas detection experts would be happy to walk through some common questions to better select the right device that fits your individual needs and environmental requirements.

    Feel free to speak to an expert at or (877) 678 - 4259

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