Industrial gas leak detection is a safety-critical discipline that uses specialised instruments to identify fugitive emissions of combustible, toxic, or asphyxiant gases before concentrations reach dangerous levels. Preventing explosions, fires, and occupational health incidents. In Singapore, the Workplace Safety and Health Act (WSHA) and its subsidiary regulations, enforced by the Ministry of Manpower (MOM), place clear obligations on employers to monitor workplace atmospheres where hazardous gases may be present. The Singapore Civil Defence Force (SCDF) additionally regulates storage and use of flammable and toxic substances under the Fire Safety Act and Dangerous Goods regulations.
Why Gas Leak Detection is Mandatory in Singapore
Singapore's high-density industrial zones (Jurong Island, Tuas, Senoko, Ayer Rajah) concentrate oil refining, petrochemical processing, pharmaceutical manufacturing, electronics fabrication and power generation near residential areas, so a gas release at any facility risks casualties beyond the site boundary. MOM's WSHA (General Provisions) Regulations require employers to assess hazardous substance risks, implement controls and monitor workplace air quality, with WSHA (First Aid) and (Risk Management) Regulations adding documentation obligations; for flammable gas installations, the Petroleum Act and SCDF-administered Dangerous Goods (General) Regulations require approved gas detection systems in defined hazardous areas. Beyond compliance, a gas leak programme reduces unplanned shutdowns, minimises fugitive emissions (an EMA licence condition for many facilities), and demonstrates due diligence to insurers — see our related article on compressed air leak detection.
Gas Detection Technologies
Catalytic bead (pellistor) sensors are the workhorse for combustible gas detection: a catalytic bead oxidises flammable gas, producing heat measured as resistance change via a Wheatstone bridge, output typically 0–100% LEL. Robust and cost-effective, responding to virtually all combustible gases (methane, propane, butane, hydrogen, solvent vapours), but requiring oxygen to function, susceptible to poisoning by silicones and halogenated compounds, and needing annual calibration per ISA-12.13.02. Infrared (IR) sensors measure gas-specific infrared light absorption — point IR uses an optical bench, open-path IR projects a beam across up to 200m and alarms on any gas cloud in the path. They work in oxygen-depleted atmospheres, can't be poisoned, and some designs fail to alarm rather than fail to safe, but cost more and can't detect hydrogen — suited to hydrocarbon detection in confined spaces, offshore platforms and ATEX Zone 1 locations. Electrochemical sensors detect toxic gases by oxidising or reducing the target at an electrode, generating current proportional to concentration in ppm, with dedicated sensors for CO, H2S, NO2, chlorine, ammonia and dozens of other toxics — they drift with temperature and humidity, have limited 2–3 year lifespans, and need regular calibration for alarm reliability. Photoionisation detectors (PID) use high-energy UV light to ionise VOCs, detecting a wide range at sub-ppm concentrations but missing methane, most inorganic gases and anything above the lamp's ionisation potential — used for VOC screening in soil remediation, cleanroom qualification and industrial hygiene surveys. Ultrasonic gas leak detectors pick up the 25–100 kHz ultrasonic noise generated by gas escaping through an orifice or crack, independent of gas type, concentration or wind direction, immune to dilution and effective in open outdoor areas where concentration-based detectors are unreliable — Coltraco Ultrasonics produces instruments for this application.
Gas Detection for Specific Target Gases
| Gas | Hazard Type | Recommended Sensor | Key Alarm Threshold |
|---|---|---|---|
| Methane (natural gas) | Combustible | Catalytic bead or IR | 10–20% LEL |
| LPG (propane/butane) | Combustible | Catalytic bead or IR | 10–20% LEL |
| Hydrogen | Combustible | Catalytic bead (H2-spec) or thermal conductivity | 10% LEL |
| Carbon monoxide | Toxic | Electrochemical | 25 ppm TWA / 100 ppm STEL |
| Hydrogen sulphide | Toxic | Electrochemical | 1 ppm TWA / 5 ppm STEL |
| Ammonia | Toxic / combustible | Electrochemical or IR | 25 ppm TWA / 35 ppm STEL |
| Chlorine | Toxic | Electrochemical | 0.5 ppm TWA / 1 ppm STEL |
| Oxygen (deficiency/enrichment) | Asphyxiant / oxidiser | Electrochemical | <19.5% or >23.5% |
| VOCs (general) | Toxic / flammable | PID | Application-specific |
Alarm thresholds for toxic gases are set relative to MOM's permissible exposure limits (PELs), which align with Singapore's Workplace Safety and Health (Chemical Agents) Regulations. TWA = time-weighted average over 8 hours; STEL = short-term exposure limit over 15 minutes.
Fixed versus Portable Gas Detection Systems
Fixed systems use permanently installed sensors wired to a central controller that annunciates alarms, activates ventilation and integrates with plant shutdown systems, providing continuous 24/7 monitoring required in ATEX classified zones, confined spaces with permanent access restrictions, and areas where toxic releases could occur without personnel present — SCDF requires approved fixed detection in facilities storing certain dangerous goods classes above specified quantities, with system design documented in a Safety Case or Major Hazard Installation report where applicable. Portable multi-gas detectors (typically O2, CO, H2S, plus one combustible gas) are mandatory PPE for confined space entry under MOM's WSHA (Confined Spaces) Regulations — an atmosphere test with a calibrated instrument must be conducted and recorded before entry, with continuous monitoring during work. Portable detectors need a bump test before each use and formal calibration at manufacturer-specified intervals, typically 3–6 months, using certified calibration gas mixtures with documented traceable certificates.
Calibration, Placement and Maintenance
Gas detector calibration is a regulatory requirement and safety imperative — an uncalibrated detector may read low (failing to alarm at a real release) or high (causing unnecessary evacuations), both carrying serious consequences. Calibration exposes the sensor to a certified calibration gas mixture at a known concentration and adjusts the response accordingly; span gas concentration must be at least 25% of the target gas's LEL or alarm setpoint, with calibration cylinders carrying a certificate of analysis showing mixture concentration and uncertainty. Unitest Instruments provides calibration services for gas detection instruments under SAC-SINGLAS accreditation, the strongest evidence of compliance for MOM inspections and ISO 45001 audits. Sensor placement significantly affects detection effectiveness: gases lighter than air (methane, hydrogen, ammonia) rise, so sensors go high; heavier-than-air gases (LPG, H2S, most refrigerants) sink, so sensors go low; sensors should sit within 3–5m downwind of likely leak points (flanges, valves, pump seals, relief valve outlets); avoid dead spots with no air movement or direct airflow paths that dilute concentrations; and sensors must be accessible for calibration without scaffolding. A documented maintenance programme should include daily/pre-shift bump tests for portable detectors in confined space entry, monthly functional checks of fixed detector alarms and relays, quarterly or 6-monthly sensor calibration with certified span gas, annual electrochemical cell replacement per manufacturer lifespan, and annual review of sensor placement against process changes.