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.
This guide covers the principal detection technologies, the gases they target, selection criteria, and the regulatory framework Singapore facilities must navigate.
Why Gas Leak Detection is Mandatory in Singapore
Singapore's high-density industrial zones — Jurong Island, Tuas, Senoko, and Ayer Rajah — concentrate oil refining, petrochemical processing, pharmaceutical manufacturing, electronics fabrication, and power generation in proximity to residential areas. A gas release incident at any of these facilities has the potential for casualties well beyond the site boundary.
MOM's WSHA (General Provisions) Regulations require employers to assess risks from hazardous substances, implement controls, and monitor workplace air quality. The WSHA (First Aid) Regulations and the WSHA (Risk Management) Regulations add specific documentation and monitoring obligations. For flammable gas installations, the Petroleum Act and the Dangerous Goods (General) Regulations (administered by SCDF) require approved gas detection systems in defined hazardous areas.
Beyond regulatory compliance, a gas leak detection programme reduces unplanned production shutdowns, minimises fugitive emissions (an environmental and EMA licence condition for many facilities), and demonstrates due diligence to insurers and clients. Our article on compressed air leak detection and energy savings covers one specific gas leak application in detail.
Gas Detection Technologies
Catalytic Bead (Pellistor) Sensors
The workhorse technology for combustible gas detection. The sensor contains a catalytic bead that oxidises flammable gas on its surface, producing heat that changes electrical resistance — measured in a Wheatstone bridge circuit. Output is typically 0–100% LEL (Lower Explosive Limit).
Pellistor sensors are robust, cost-effective, and respond to virtually all combustible gases including methane, propane, butane, hydrogen, and solvent vapours. Limitations: they require oxygen to function (fail in oxygen-depleted atmospheres), can be poisoned by silicones and halogenated compounds, and do not detect hydrogen safely above certain concentrations. Calibration is required at least annually per ISA-12.13.02.
Infrared (IR) Sensors
IR sensors measure gas concentration by the absorption of infrared light at a wavelength specific to the target gas. Point IR sensors use an optical bench with a source and detector; open-path IR sensors project a beam across an open area (up to 200 m) and alarm when any cloud of gas in the path reaches alarm concentration.
Advantages over catalytic beads: they work in oxygen-depleted atmospheres, cannot be poisoned, and some designs are intrinsically immune to sensor failures going undetected (they fail to alarm rather than to safe). Disadvantages: higher cost, cannot detect hydrogen (no IR absorption band). IR sensors are suited to hydrocarbon gas detection in confined spaces, offshore platforms, and ATEX Zone 1 locations.
Electrochemical Sensors
Electrochemical cells detect toxic gases by oxidising or reducing the target gas at an electrode, generating a current proportional to concentration. They are highly specific to the target gas — carbon monoxide, hydrogen sulphide, nitrogen dioxide, chlorine, ammonia, and dozens of other toxics each have dedicated electrochemical sensors. Output is typically in ppm (parts per million).
Electrochemical sensors drift with temperature and humidity, have limited lifespans (typically 2–3 years), and are cross-sensitive to some other gases. Regular calibration — at intervals specified by the manufacturer and required by MOM inspection regimes — is essential to maintain alarm reliability.
Photoionisation Detectors (PID)
PID instruments use high-energy UV light to ionise volatile organic compounds (VOCs), generating a measurable ion current. They detect a very wide range of VOCs at extremely low concentrations (sub-ppm) but cannot detect methane, most inorganic gases, or anything with an ionisation potential above the lamp energy. PIDs are used for VOC screening in soil remediation, cleanroom qualification, and industrial hygiene surveys.
Ultrasonic Gas Leak Detectors
Pressurised gas escaping through a small orifice or crack generates ultrasonic noise in the 25–100 kHz range. Ultrasonic detectors pick up this airborne ultrasound independently of gas type, concentration, or wind direction. They are immune to dilution effects and respond to leaks in open, well-ventilated outdoor areas where concentration-based detectors would be unreliable. Coltraco Ultrasonics — one of Unitest Instruments' authorised brands — produces ultrasonic instruments used for exactly this application. View Coltraco Ultrasonics products.
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 Gas Detection
Fixed systems use permanently installed sensors wired to a central controller that annunciates alarms, activates ventilation, and integrates with plant shutdown systems. They provide continuous 24/7 monitoring and are required in ATEX classified zones, confined spaces with permanent access restrictions, and areas where toxic gas releases could occur without personnel present.
Singapore's SCDF requires approved fixed gas detection in facilities storing certain classes of dangerous goods above specified quantities. The system design — sensor placement, alarm levels, response actions — must be documented in a Safety Case or Major Hazard Installation safety report for applicable facilities.
Portable Gas Detectors
Portable multi-gas detectors (typically monitoring O2, CO, H2S, and one combustible gas simultaneously) are mandatory personal protective equipment for confined space entry under MOM's WSHA (Confined Spaces) Regulations. Before any confined space entry, an atmosphere test must be conducted with a calibrated instrument and the result recorded. During work in confined spaces, continuous monitoring is required.
Portable detectors must be bump-tested (functional check) before each use and formally calibrated at intervals specified by the manufacturer — typically 3 to 6 months. All calibrations should use certified calibration gas mixtures and be documented with traceable certificates.
Calibration Requirements for Gas Detectors
Gas detector calibration is not optional — it is a regulatory requirement and a safety imperative. An uncalibrated detector may read low (failing to alarm at a real gas release) or high (causing unnecessary evacuations and production losses). Both failure modes carry serious consequences.
Calibration involves exposing the sensor to a certified calibration gas mixture at a known concentration and adjusting the instrument's response accordingly. Span gas concentration must be at least 25% of the target gas's LEL or alarm setpoint. Calibration gas cylinders must have a certificate of analysis showing the actual mixture concentration and its uncertainty.
Unitest Instruments provides calibration services for gas detection instruments under its SAC-SINGLAS accreditation. Calibration records issued by an accredited laboratory are the strongest evidence of compliance for MOM inspections and ISO 45001 occupational health and safety audits.
Sensor Placement Best Practices
Sensor location significantly affects detection effectiveness. Key principles:
- Density relative to air — gases lighter than air (methane, hydrogen, ammonia) rise and accumulate at ceiling level; sensors should be placed high. Heavier-than-air gases (LPG, H2S, most refrigerants) sink to floor level; sensors go low.
- Near potential leak sources — flanges, valves, pump seals, and relief valve outlets are the most likely leak points; sensors should be downwind of these within 3–5 m.
- Not in dead spots — avoid placing sensors in areas with no air movement, where gas might accumulate without reaching the sensor, or in direct airflow paths that dilute concentrations before detection.
- Accessible for calibration and maintenance — sensors must be reachable without scaffolding or specialist access equipment to enable routine maintenance.
Inspection and Maintenance Obligations
Gas detection systems require a documented maintenance programme. At minimum:
- Daily or pre-shift bump test for portable detectors used in confined space entry
- Monthly functional check of fixed detector alarm outputs and relay functions
- Quarterly or 6-monthly sensor calibration with certified span gas
- Annual sensor replacement for electrochemical cells (manufacturer-specified lifespan)
- Annual review of sensor placement against process changes
Contact Unitest Instruments to discuss gas detection equipment supply and calibration services for your Singapore facility. Our team can advise on sensor selection, calibration scheduling, and compliance documentation.