| Single-gas personal monitor | One target gas, commonly oxygen, carbon monoxide, hydrogen sulfide, or a specified toxic gas | Electrochemical for many toxic gases; electrochemical or other application-specific technology for oxygen | Gas- and sensor-dependent; oxygen monitors commonly measure approximately 0–25% volume | Personal exposure monitoring and task-specific work areas | Choose the target gas, alarm limits, sensor range, and approvals required by the worksite risk assessment. | Perform a function or bump test before use according to the manufacturer’s instructions and site policy. Calibrate when required by the test result, service history, or applicable procedure. |
| Four-gas personal monitor | Commonly oxygen, combustible gas, carbon monoxide, and hydrogen sulfide | Usually electrochemical sensors for oxygen and toxic gases, plus a catalytic-bead or infrared sensor for combustibles | Typical configurations include oxygen near 0–25% volume, toxic-gas ranges in ppm, and combustibles displayed as %LEL | General industrial work, confined-space entry support, and emergency response screening | Confirm that the combustible sensor is suitable for the expected gases and that sensor limitations, oxygen dependence, and poisoning risks are understood. | Check alarms, battery, sensor status, and inlet before use. Bump-test and calibrate using the specified test gas, regulator, tubing, and procedure. |
| Multi-gas monitor with expanded sensor options | Several toxic gases, oxygen, and combustible gases; sensor combinations vary by configuration | Electrochemical, catalytic-bead, infrared, or other sensor technologies selected for the target gases | Depends on the installed sensors; ranges may be expressed in ppm, %LEL, or % volume | Industrial facilities with changing hazards or multiple target gases | Match every installed sensor to the hazard assessment; additional channels do not guarantee detection of every gas. | Maintain a sensor inventory and calibration record. Use compatible certified test gas and check cross-sensitivity, sensor life, and calibration status. |
| Combustible-gas monitor | Flammable gases or vapors, reported as a percentage of the lower explosive limit (%LEL) | Catalytic-bead or infrared, depending on gas, environment, and application | Commonly 0–100% LEL; the actual range and response depend on the instrument and target gas | Leak checks, hot-work area checks, and flammable-atmosphere assessment | Verify response to the target gas. Catalytic sensors can be affected by some poisons and may require sufficient oxygen; infrared sensors do not measure every combustible gas. | Use the specified calibration gas and correction factors where applicable. Keep the inlet clean and follow the prescribed bump-test and calibration schedule. |
| Photoionization detector (PID) | Many volatile organic compounds (VOCs); response varies by compound and lamp energy | Ultraviolet photoionization sensor | Often displayed in ppm, with range and resolution dependent on the instrument configuration | VOC screening, leak investigation, and industrial hygiene surveys | A PID is not a universal VOC identifier. Check the compound’s ionization potential, correction factor, humidity effects, and whether the lamp energy is suitable. | Zero and calibrate with the specified gas. Inspect and clean the lamp and sensor chamber as directed, and replace damaged or contaminated components. |
| Infrared gas monitor | Selected gases detectable by the instrument’s infrared absorption method, often including certain hydrocarbons or carbon dioxide | Non-dispersive infrared (NDIR) or another application-specific infrared method | Gas-specific; may be displayed in ppm, % volume, or %LEL | Applications where infrared detection is appropriate, including some oxygen-deficient or sensor-poisoning environments | Confirm the target gas is detectable by the selected infrared sensor. Infrared instruments generally do not detect hydrogen. | Follow gas-specific calibration instructions. Keep optical paths and sample openings clear, and check the device after exposure to dust, moisture, or impact. |
| Pumped portable monitor | One or more gases, depending on the fitted sensors and sampling configuration | Sensor technology varies; an internal pump draws a sample through a probe or tubing | Determined by the installed sensors; sample response time depends on tubing length, flow, and gas properties | Remote sampling of tanks, pits, vessels, and other locations that cannot be safely approached directly | Use the correct tubing and probe. Allow for transport and sensor response time, and never enter a hazardous area solely to collect a sample. | Perform a flow or blockage check before sampling. Inspect tubing, filters, water traps, and pump alarms; bump-test and calibrate the monitor as specified. |