Introduction
In the high-stakes world of oil & gas, petrochemical, and chemical manufacturing, the risk of fires, explosions, and toxic gas leaks is a constant concern. One of the most crucial layers of protection against such hazards is the Fire and Gas (F&G) Detection System. These systems form a vital part of the Layer of Protection Analysis (LOPA) and are critical to ensuring timely detection and response to incidents.
A Fire and Gas Detector Location or Mapping Study ensures the strategic placement of flame and gas detectors to maximize area coverage, reduce blind spots, and improve system reliability. It is not just a regulatory formality, but a life-saving engineering practice that ensures operational integrity.
What is a Fire and Gas Detector Mapping Study?
A Fire and Gas Mapping Study is a systematic and risk-based engineering analysis that evaluates the effectiveness of flame and gas detectors in covering high-risk zones. The study uses 2D layouts or 3D digital models to simulate the coverage provided by detectors and determine the optimal quantity, type, and location.
The primary goals are:
- Minimize the time to detect a leak or flame.
- Ensure redundant coverage for critical zones.
- Optimize detector count to balance safety and cost.
- Demonstrate compliance with industry codes and SIL studies.
Why is Detector Mapping Important?
Here’s why the study is vital in any modern process facility:
1. Improves Detection Efficiency
Ensures that no major hazard area is left unmonitored or inadequately covered.
2. Supports Functional Safety
Contributes to achieving SIL (Safety Integrity Level) requirements of the overall safety instrumented system (SIS).
3. Compliance & Risk Mitigation
Helps satisfy regulatory bodies, including OISD, PESO, and international agencies.
4. Reduces False Alarms and Nuisance Trips
Proper detector orientation and type selection reduce false positives.
5. Enables Emergency Response
Timely detection triggers alarms, firefighting systems, and plant shutdown logic.
Types of Detectors Considered
A. Gas Detectors
- Point-type Gas Detectors
- Detect combustible or toxic gases at specific points.
- Best for localized leak detection.
- Open-path Gas Detectors
- Use infrared or laser beams to detect gas across longer distances.
- Ideal for fence-line and corridor protection.
- Ultrasonic Gas Leak Detectors
- Sense high-frequency sound from pressurized gas leaks.
- Effective even in windy or ventilated areas.
B. Fire Detectors
- Flame Detectors
- UV, IR, UV/IR, MSIR (multi-spectrum infrared)
- Require a direct line of sight.
- Smoke Detectors
- Optical or ionization-based.
- More useful in enclosed environments.
- Heat Detectors
- Fixed or rate-of-rise.
- Act slower, used in enclosed or electrically sensitive zones.
Codes and Standards Followed
Below are essential standards and practices that guide detector mapping:
| Standard | Description |
|---|---|
| ISA TR84.00.07 | Guidance on Fire and Gas Detection System Performance |
| NFPA 72 | Fire Alarm and Signaling Code |
| API RP 14C / 14J | Safety System Design for Offshore Production |
| EN 60079-29 | Gas Detection Equipment Requirements |
| OISD Standards (India) | Safety guidelines for oil & gas installations |
| ISO 23251 | Pressure-relief and hazard protection |
👉 Internal Link: List of Process Safety Standards & Guidelines
Methodology for Fire and Gas Mapping Study
The process typically includes the following steps:
1. Input Data Collection
- Plot plans, equipment layout, elevation drawings
- Hazardous area classification (Zone 0, 1, 2)
- Process hazard scenarios (from HAZOP/QRA)
- Ventilation and wind data (if available)
- Equipment and piping that could act as obstruction
2. Define Risk Zones
- Identify high-risk equipment (compressors, furnaces, tanks)
- Define gas release points
- Classify areas based on severity and likelihood
3. Simulation with Tools
- Build or import 3D model (AutoCAD, PDS, SmartPlant)
- Input parameters for each detector type (e.g., cone of vision, range, coverage angle)
- Simulate coverage and identify blind spots
4. Coverage Evaluation
- % area covered for fire and gas hazards
- Heat maps generated for visibility
- Minimum target: 90–95% coverage depending on criticality
5. Optimization
- Rotate or elevate detectors
- Add redundancy where required
- Remove unnecessary detectors
6. Documentation
- Final detector location plan
- Simulation reports
- Justification notes for deviations
- SIL verification support
Software Tools Used
| Tool | Functionality |
|---|---|
| Kenexis Effigy™ | Risk-based F&G mapping with quantitative coverage |
| Det-Tronics FDT | Flame detector placement with cone-of-vision modeling |
| Honeywell Fire & Gas Mapper | Coverage analysis for open-path and flame detectors |
| AutoCAD / Revit | 2D/3D modeling of plant layout |
| PHAST / FLACS | For advanced dispersion modeling and scenario validation |
👉 Internal Link: PHAST-Based Dispersion Study
Detector Placement Guidelines
🔥 Flame Detectors
- Line of sight is critical.
- Avoid obstruction from pipes, vessels, or structures.
- Height: Typically 2.5–3.5 meters above grade.
💨 Gas Detectors
- Point detectors at ~0.3m (for heavier gases like propane) or ~1.5m (for lighter gases like H₂).
- Near potential leak sources: pumps, flanges, valves.
- Near ventilation outlets and drains.
Redundancy
- Overlapping coverage is mandatory in high-risk areas.
- Use 2ooN voting logic to avoid false shutdowns.
Example Coverage Criteria
| Zone Type | Target Gas Coverage | Target Fire Coverage |
|---|---|---|
| Critical Zone (e.g., compressor deck) | >95% | >90% |
| Non-critical Open Zone | 70–85% | 60–75% |
| Enclosed Zone | Full redundancy | Near-total fire coverage |
Case Study: Refinery Pump House
Scenario: High-density hydrocarbon processing unit with multiple pump skids
- Risks Identified:
- Diesel and naphtha leak points
- Electrical ignition sources
- Detectors Proposed:
- 8 flame detectors (UV/IR)
- 10 point IR gas detectors
- 2 open-path detectors (10m path length)
- Simulation Results:
- Fire coverage = 92%
- Gas coverage = 96%
- 2 blind spots resolved by adding flame detector at 3.2m elevation
- SIL Study: Compliant with SIL 2 requirement
Integration with Safety Instrumented Systems (SIS)
- Detectors output signals are integrated with Fire & Gas Control Panel (FGCP).
- Interlinked with Emergency Shutdown (ESD) systems.
- Configured with SIL-rated PLCs for reliability.
- Alarms categorized based on consequence:
- Local Alarm
- Shutdown Logic Initiation
- Fire Water Deluge Trigger
Validation and Maintenance
Commissioning Stage
- Site verification of detector positions
- Line-of-sight checks for flame detectors
- Test alarm circuits and shutdown interlocks
Operational Stage
- Routine calibration (as per O&M manual)
- Quarterly inspection of visibility and accessibility
- Annual performance testing
Common Pitfalls and How to Avoid Them
| Mistake | Correction |
|---|---|
| Overdependence on vendor layout | Validate using 3rd-party F&G mapping |
| Obstruction not considered | Import full 3D model with piping |
| No allowance for future expansion | Consider spare detectors or flexible layout |
| One detector per area | Apply redundancy for high-SIL areas |
| No review of wind dispersion | Use PHAST or CFD |
India-Specific Challenges
- Limited availability of plant 3D models
- Cost pressures pushing for fewer detectors
- Gaps in understanding of ISA TR84.00.07
- Resistance to third-party reviews
- Difficulty in validating detector placement on-site
FAQs
Q1: How many detectors are typically needed?
It depends on the size and risk profile, but a typical medium unit might have 10–15 flame detectors and 20–30 gas detectors.
Q2: How do you ensure there are no blind spots?
Use mapping software to simulate coverage and adjust placement iteratively.
Q3: How does wind affect gas detector coverage?
It can blow lighter gases away from detectors. That’s why dispersion modeling is crucial.
Q4: Is the mapping study required by law?
Not explicitly, but required to meet functional safety and design expectations per industry standards.
Conclusion
Fire and Gas Detector Mapping Study is no longer a luxury or post-incident remedy. It is a proactive safety measure that forms the backbone of risk mitigation in hazardous industries. With advanced tools, standards like ISA TR84.00.07, and third-party validations, facilities can now ensure maximum coverage, faster detection, and greater plant integrity.
By investing in such studies, organizations not only comply with safety norms but also protect lives, assets, and the environment — a true win-win for everyone.
👉 Internal Link: List of Process Safety Studies in Oil & Gas
