Understanding 4 Gas Monitors: How They Work & Why They Are Important

Understanding 4 Gas Monitors: How They Work & Why They Are Important

In today’s increasingly dynamic industrial landscape, 4 gas monitors have emerged as critical components of workplace safety. These versatile devices simultaneously detect and measure the presence of multiple atmospheric hazards, providing crucial information for worker safety and well-being.

Below, we delve into the intricacies of this essential safety equipment and provide practical guidance for using and maintaining them.

What does a 4 gas monitor detect?

A 4 gas monitor detects the concentration of multiple gases simultaneously. Depending on its intended application, a 4 gas detector can alert workers to the following atmospheric hazards:

  • Carbon Monoxide (CO): A colorless, odorless gas, CO can be lethal in high concentrations. A 4 gas detector monitors CO concentration levels, minimizing the risks associated with prolonged exposure.
  • Hydrogen Sulfide (H2S): Commonly found in industries such as oil and gas, wastewater treatment, and agriculture, H2S is a highly toxic gas. Even low-level exposure can cause respiratory problems, eye irritation, and loss of smell.
  • Methane (CH4): Methane leaks can occur during the production and processing of natural gas and agricultural and mining processes. Dangerous CH4 levels can lead to explosions, asphyxiation, and poisoning.
  • Oxygen (O2): Insufficient oxygen levels can lead to hypoxia, potentially inducing dizziness, confusion, and loss of consciousness.
  • Combustible Gases: Gases or vapors such as propane, hydrogen, and other hydrocarbons can leak from pipelines, tanks, and valves or accumulate in confined spaces. They can cause fires or explosions when ignited by sparks, flames, or static electricity.

Depending on the required application, you can configure a 4 gas monitor to detect a wide variety of gases. BW Honeywell’s Flex4, for instance, is compatible with up to 15 different sensors and allows you to monitor up to five hazardous gases at the same time.

Diffusion Monitors vs. Sample Draw Monitors: A Closer Look

Gas monitors are typically either diffusion-based or pump-based. Diffusion monitors rely on natural air movement to reach the sensors. Meanwhile, pump-based models actively draw air samples, offering quicker response times and better sensitivity for detecting low gas concentrations.

The ideal gas monitoring system depends on the specific needs of the industry and the nature of the workplace environment. Let’s delve into the characteristics of each:

Diffusion Monitors

A diffusion monitor works by positioning it in the monitored environment. As the gases enter the sensor chamber, the internal sensors respond to the presence and concentration of each gas. They’re commonly used in open or well-ventilated spaces, offering a simple and effective solution for continuous gas monitoring without needing an external sampling pump.


  • Continuous monitoring: Diffusion gas monitors can continuously monitor the air for atmospheric hazards.
  • Versatility: These devices have a wide range of applications, including personal safety, industrial process monitoring, and environmental monitoring.

While diffusion monitors are primarily designed for open-air environments, BW Honeywell’s MCXL has an available confined-space entry accessory kit. The kit provides everything you need for remote air sampling, allowing you to leverage the monitor’s full range of capabilities.

Sample Draw Monitors

These gas monitors actively draw samples from remote locations using a pump. This allows for a more controlled and accurate air sampling, ensuring the safety of workers before entering a space.


  • Flexibility: You can strategically position the sampling tube to target specific areas of concern, even confined spaces or areas behind barriers.
  • Operation in harsh environments: The tubing allows you to place the sensor in areas with extreme temperatures, humidity, or particulate matter. A diffusion sensor may not properly function in such environments.
  • Faster response time: Sample draw pumps actively pull in air, significantly reducing the time it takes for the sensor to detect gas and measure concentration.


  • More complex and expensive: These monitors require a pump, tubing, and additional components compared to simpler diffusion monitors.
  • Requires frequent maintenance: Sample draw monitors require regular pump maintenance and tubing checks for optimal performance.
  • High power consumption: Pumps typically require more power than passive diffusion monitors.

For work conditions that require the best of both worlds, GfG’s Microtector II G450 features an Alkaline Smart Pump with two operating modes: diffusion and remote sample draw. Combined with automated calibration and event and data logging, it’s a truly powerful multi-gas monitor, with its sensors backed by a three-year warranty.

How to bump test a 4 gas monitor

Bump testing simulates gas exposure to verify the sensor’s functionality and alarm system. Perform this before each use or work shift:

  • Select a test gas: Choose a certified test gas that corresponds to the gases your monitor is designed to detect.
  • Ensure proper setup: Securely connect the gas cylinder to the monitor’s bump test adapter.
  • Initiate bump test mode: Follow the manufacturer’s instructions to activate the monitor’s bump test mode.
  • Expose the sensors to the test gas: Briefly expose the monitor to the test gas, typically around 10 seconds.
  • Verify readings: Check the monitor’s display to ensure it registers the expected concentrations of the test gas.
  • Document results: Record the bump test results, including any deviations from the expected readings. Maintaining these records can be valuable for safety compliance, troubleshooting purposes, and knowing if you have an expired gas monitor.

Docking stations help automate several routine maintenance tasks for gas detection equipment and provide documentation for these processes. For example, the BW IntelliDox performs the quickest bump test in the industry, resulting in increased uptime and no wasted calibration gas. If your gas detector fails a bump test, it will need to be calibrated.

How to calibrate a 4 gas monitor

Gas monitor calibration ensures the accuracy of sensor readings by adjusting them to known gas concentrations. Perform this according to the manufacturer’s recommendations.

  • Follow the specific calibration procedures: Refer to the manual for detailed instructions and the required gas mixtures.
  • Expose the sensors to calibration gas standards: Check the test gas expiration date and ensure the concentration is high enough to trigger the alarm.
  • Adjust sensor settings as needed: Adjust the readings to match the known concentration of the calibration gas. Depending on the device, the monitor might guide you through this process automatically or manually.
  • Verify calibration: Perform a post-calibration bump test to confirm that the monitor responds accurately to the targeted gas concentrations.
  • Document calibration data: Include the date, time, gas used, and calibration results for traceability.

When calibrating a 4 gas monitor, the readings should be within the acceptable range of the test gas concentration. The range is typically +/- 10%–20% of the test gas concentration. If the monitor doesn’t recalibrate or the alarm isn’t triggered, try recalibrating the monitor, using a new test gas, or contacting the manufacturer or retailer for assistance. Sometimes, cleaning a gas monitor is all you need. We recommend bump testing regularly and calibrating at least every six months.

How to use a 4 gas monitor

Always follow the manufacturer’s instructions for safe and effective use. Below are general guidelines for proper gas monitor usage:

  • Power on and perform self-test: Turn the monitor on and allow it to complete its self-test. Ensure proper functionality before entering potentially hazardous areas.
  • Wear the monitor correctly: Position the monitor where it can accurately sample the surrounding air. Consider factors such as proximity to potential gas sources and the worker’s breathing zone. This may require a gas monitor mount for optimal placement.
  • Understand the alarms: Familiarize yourself with the monitor’s alarm thresholds and settings. In the event of an alarm, take immediate action based on the nature and severity of the alert. This may involve following established protocols and evacuating the area.

If your gas detection equipment needs calibration or diagnosis for potential repair, we can help! PK Safety is a factory-authorized service center for BW Technologies by Honeywell, RAE Systems, and RKI Instruments.

Contact us today to learn more about 4 gas monitors and other workplace safety equipment or to dispose of a gas monitor safely.


Apr 8th 2024 PK Safety Team

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