| Combustible Gas | 0–100% LEL | 1% LEL | Catalytic bead or infrared | 10% and 20% LEL | Leak detection, confined-space entry, process-area monitoring | Confirm the calibration gas, target-gas response factors, oxygen dependency, and resistance to sensor poisoning. |
| Oxygen (O₂) | 0–30% volume | 0.1% volume | Electrochemical | Low: 19.5%; high: 23.5% | Confined spaces, tanks, manholes, laboratories, and industrial maintenance | Alarm values should be adjusted to the applicable occupational-safety rules and site risk assessment. |
| Carbon Monoxide (CO) | 0–500 ppm | 1 ppm | Electrochemical | 35–50 ppm low; 100–200 ppm high | Combustion areas, boiler rooms, garages, mining, and emergency response | Check cross-sensitivity to hydrogen and other interfering gases, especially in industrial environments. |
| Hydrogen Sulfide (H₂S) | 0–100 ppm | 0.1 ppm | Electrochemical | 5–10 ppm low; 10–20 ppm high | Oil and gas, wastewater, sewers, agriculture, and confined spaces | Use a low-range sensor for toxic exposure monitoring; high concentrations can rapidly impair the sense of smell. |
| Sulfur Dioxide (SO₂) | 0–20 ppm | 0.1 ppm | Electrochemical | 1–2 ppm low; 5 ppm high | Combustion plants, metal processing, pulp and paper, and chemical handling | Verify humidity performance, cross-interference, and whether the selected detector supports the required sensor module. |
| Nitrogen Dioxide (NO₂) | 0–20 ppm | 0.1 ppm | Electrochemical | 1–3 ppm low; 5 ppm high | Diesel exhaust, tunnels, underground work, welding, and engine rooms | Allow sufficient response time and confirm compatibility with other installed electrochemical sensors. |
| Ammonia (NH₃) | 0–100 ppm | 1 ppm | Electrochemical or photoionization-based configuration | 25 ppm low; 35–50 ppm high | Refrigeration, fertilizer production, food processing, and livestock facilities | Check sensor lifetime, material compatibility, temperature limits, and recovery time after high exposure. |
| Chlorine (Cl₂) | 0–10 ppm | 0.1 ppm | Electrochemical | 0.5–1 ppm low; 2–5 ppm high | Water treatment, disinfection, chemical plants, and swimming-pool facilities | Confirm the detector’s resistance to corrosive atmospheres and its recommended calibration procedure. |
| Volatile Organic Compounds | 0–2,000 ppm | 0.1–1 ppm | Photoionization detector, typically with a 10.6 eV lamp | Site-specific; often 10–50 ppm | Solvents, petrochemical operations, coatings, laboratories, and spill response | Readings depend strongly on the compound’s ionization potential; apply correction factors for individual VOCs. |