| 1. Risk Assessment | Gas hazard profile | Identify every toxic, flammable, oxygen-deficient, or oxygen-enriched atmosphere that could occur during normal operation, startup, shutdown, cleaning, maintenance, or an accidental release. | Document gas properties, exposure risks, release sources, ventilation conditions, occupancy, and potential accumulation points. | Approved gas hazard assessment, process drawings, safety data sheets, and operating scenario review. |
| 2. Sensor Selection | Detection technology | Match the sensor technology to the gas and operating environment. Common options include electrochemical, catalytic bead, infrared, photoionization, and oxygen sensors. | Check selectivity, cross-sensitivity, response time, expected service life, humidity tolerance, temperature range, and resistance to contaminants. | Application suitability statement and manufacturer technical documentation without relying on brand-specific data. |
| 3. Alarm Levels | Set points and actions | Define low, high, and where necessary, high-high alarm levels based on applicable occupational exposure limits, lower explosive limit requirements, process safety rules, and emergency procedures. | Alarm thresholds must be consistent with the gas type, measurement unit, local regulations, evacuation strategy, and ventilation response. | Cause-and-effect matrix showing alarm level, notification method, ventilation response, shutdown action, and responsible personnel. |
| 4. Detector Location | Placement strategy | Place detectors near credible release points and in areas where gas may accumulate. Consider gas density, airflow, obstructions, access, and worker breathing zones. | Light gases may collect at high points, while heavier gases may collect in pits, trenches, drains, or low areas. Airflow can change the practical location. | Marked detector layout, airflow review, coverage assessment, and documented justification for each detector position. |
| 5. Environmental Conditions | Area classification and enclosure | Select equipment suitable for the hazardous area classification and the site environment, including dust, moisture, vibration, corrosion, and temperature extremes. | Verify ingress protection, electrical classification, materials of construction, cable entries, grounding, and compatibility with cleaning chemicals. | Area classification drawing, equipment certificates, installation records, and environmental compatibility review. |
| 6. System Architecture | Communication and reliability | Choose standalone, controller-based, or integrated architecture according to the required coverage, alarm management, control functions, and consequence of system failure. | Consider wired or wireless communication, power supply monitoring, battery backup, fault indication, signal loss response, redundancy, and integration with ventilation or shutdown systems. | System architecture diagram, power budget, communication test record, and documented fail-safe response. |
| 7. Installation | Mechanical and electrical installation | Install detectors securely, maintain access for testing, protect sensing elements from impact, and route cables according to the site electrical design. | Avoid locations blocked by equipment, exposed to direct process discharge, or made inaccessible by future construction. Follow approved wiring and grounding practices. | Installation inspection checklist, cable test results, device identification, as-built drawings, and photographic records where required. |
| 8. Commissioning | Functional verification | Test each detector, alarm output, fault signal, display, remote notification, ventilation interlock, shutdown command, and emergency power function before placing the system in service. | Use a controlled test gas or approved test method. Confirm that the indicated concentration, alarm timing, and programmed actions match the approved design. | Commissioning certificate, loop test results, alarm response test, interlock verification, and authorized acceptance record. |
| 9. Calibration | Zero and span calibration | Perform calibration using traceable reference gas with a known concentration and a suitable balance gas. Follow the equipment-specific calibration procedure. | Check cylinder expiration, regulator suitability, tubing condition, flow rate, stabilization time, environmental conditions, and sensor response before accepting the result. | Calibration certificate, reference gas certificate, cylinder identification, pre-adjustment reading, post-adjustment reading, date, technician, and next due date. |
| 10. Bump Testing | Routine response check | Expose the detector briefly to an appropriate test gas to confirm that the sensor responds and that the alarm signal reaches the intended control point. | A bump test confirms basic response but does not replace a full calibration. The interval should be determined by risk, regulations, operating history, and sensor performance. | Bump-test log showing detector identification, gas concentration, response time, alarm activation, result, and corrective action if unsuccessful. |
| 11. Maintenance | Preventive maintenance | Inspect sensors, filters, sinters, sample lines, housings, displays, cable glands, batteries, audible alarms, visual indicators, and ventilation interfaces. | Remove contamination, replace consumable parts when needed, investigate repeated faults, and keep spare sensors and test equipment within their usable dates. | Maintenance schedule, work orders, parts records, fault history, corrective action reports, and return-to-service authorization. |
| 12. Record Management | Traceability | Maintain a unique identification and complete history for every detector, controller, sensor, calibration event, alarm event, fault, repair, and configuration change. | Records should be legible, protected from unauthorized changes, available to competent personnel, and retained for the period required by site rules or applicable law. | Asset register, calibration database, alarm history, maintenance log, training records, and controlled system drawings. |
| 13. Personnel and Procedures | Competence and response | Train operators, maintenance personnel, and emergency responders on alarm meanings, evacuation or shelter procedures, detector limitations, testing methods, and reporting requirements. | Define who may inhibit alarms, change set points, perform calibration, approve repairs, and return equipment to service. | Training matrix, competency assessment, written emergency procedures, drill records, and authorization list. |
| 14. Compliance Review | Applicable standards and regulations | Review national and local occupational safety, electrical, hazardous-area, fire, environmental, and process-safety requirements that apply to the facility. | Use the current editions of applicable standards and confirm whether the system is part of a broader safety instrumented, fire and gas, or emergency shutdown function. | Compliance register, inspection findings, corrective action plan, audit report, and management approval of outstanding risks. |
| 15. Periodic Review | Performance and change management | Reassess detector coverage and settings after process changes, ventilation modifications, new chemicals, building alterations, incidents, or repeated false alarms. | Review alarm frequency, missed detections, sensor drift, nuisance alarms, response time, maintenance trends, and lessons learned from emergency exercises. | Periodic performance review, management-of-change record, updated risk assessment, revised drawings, and closed corrective actions. |
