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Detailed Comparison of Combustible Gas Detectors and Heat/Smoke Detectors: 2024 Industrial Fire Protection System Selection and Integration Guide
In industrial facilities, commercial complexes, energy infrastructure, and petrochemical engineering projects, fire and explosion risk prevention has become a core component of system integration projects. For different hazard sources, selecting the appropriate front-end detection devices directly determines the response timeliness, false alarm suppression capability, and compatibility with platforms such as BMS, SCADA, and PLC.
As a supplier specializing in industrial-grade sensors, Nexisense provides a comprehensive portfolio including laser methane detectors, infrared combustible gas detectors, heat detectors, and photoelectric smoke detectors. These products are widely deployed in system integrator and EPC projects. From an engineering perspective, this article provides a systematic comparison of combustible gas detectors and heat/smoke detectors, focusing on technology selection, installation standards, communication interfaces, linkage strategies, and real-world project implementation experience, offering reference guidance for project design and procurement in 2024–2025.
I. Comparison of Core Functions and Hazard Prevention Positioning
| Device Type | Core Monitoring Target | Primary Prevention Objective | Typical Engineering Application Scenarios | Priority Scenarios (System Integration Perspective) |
|---|---|---|---|---|
| Combustible Gas Detector | Methane, propane, hydrogen, and other combustible gas concentrations | Leak prevention → explosion prevention | Gas boiler rooms, chemical plants, LNG fueling stations, oil and gas pipeline rooms | Explosion-risk areas with combustible gas accumulation potential (Zone 1/2) |
| Heat Detector | Abnormal ambient temperature rise or rate of temperature increase | Mid-to-late stage fire temperature warning | Underground parking garages, drying workshops, power distribution rooms, cable interlayers | Low-smoke, high-dust, high-temperature steam environments |
| Smoke Detector | Smoke particles during early combustion (smoldering or flaming) | Early-stage fire warning (smoldering phase) | Offices, hotel rooms, archives, clean workshops | Conventional civil and commercial buildings with visible early smoke generation |
Summary of Fundamental Differences
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Combustible gas detectors are pre-incident preventive devices aimed at interrupting the initial link of the explosion chain (gas accumulation → ignition source).
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Heat and smoke detectors are in-incident warning devices that provide alarm signals after a fire has already occurred or is about to develop.
In large-scale projects, a “gas detector + smoke/heat detector combination” strategy is commonly adopted to establish a multi-layered risk prevention system.
II. Comparison of Technical Principles and Performance Parameters
1. Combustible Gas Detectors
Mainstream Detection Principles (Nexisense Product Lines):
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Tunable Diode Laser Absorption Spectroscopy (TDLAS): e.g., TX911-A series, targeting specific gases such as methane, with strong resistance to cross-interference and long service life (>10 years), suitable for long-distance pipeline monitoring.
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Infrared Absorption: e.g., TX721-A1B low-power series, broadband detection of multiple hydrocarbons, resistant to poisoning and aging.
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Catalytic Combustion: traditional industrial mainstream, fast response but requires regular calibration and is susceptible to silicone and sulfur compound poisoning.
Key Alarm Thresholds: Typically graded alarms at 10%–50% of LEL. A common first-level alarm is set at 10%–20% LEL (for example, methane 5% vol = 100% LEL, so 0.5%–1% vol triggers the alarm).
Response Time: Catalytic/infrared <10–15 s; laser-based <5 s (depending on optical path length).
2. Heat Detectors
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Fixed-temperature type: triggers at preset thresholds such as 57°C / 70°C / 90°C (common A2, B classes).
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Rate-of-rise type: triggers when temperature rise exceeds 5–10°C/min.
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Rate-of-rise and fixed-temperature combined type: integrates both features to improve reliability.
Limitations: Slow response to slow-developing fires (e.g., cable overload heating).
3. Smoke Detectors
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Photoelectric (mainstream): detects infrared light scattering or obstruction by smoke particles, high sensitivity and excellent response to smoldering fires.
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Ionization: gradually phased out due to environmental and false alarm issues.
Response Time: Smoldering phase 30–90 s; faster in flaming fires.
III. Installation Locations and Engineering Standards (2024 Reference)
| Item | Combustible Gas Detector | Heat Detector | Smoke Detector | Primary Standards |
|---|---|---|---|---|
| Installation Height | Lighter-than-air gases (methane, hydrogen): near ceiling; heavier-than-air gases (LPG): 0.3–0.6 m above floor | ≤0.3 m below ceiling | Ceiling center or highest point | GB 15322 series / GB 50116-2013 |
| Distance from Leak/Risk Source | ≤4 m horizontal distance from gas appliances/valves | — | — | GB 15322.1-2019 and subsequent revisions |
| Coverage Area / Spacing | Based on dispersion model, typically 8–12 m² per unit | Typically 50–80 m² per unit | 60–100 m² per unit (ceiling height <6 m) | GB 50116 Appendix E |
| Interference Avoidance | Avoid oil fumes, steam jets, and exhaust outlets | Keep ≥1.5 m from air-conditioning outlets | Avoid kitchen oil fumes and bathroom steam | GB 50116-2013 |
2024 Update Note: Refer to GB/T 20936.2-2024 (Selection, Installation, Use, and Maintenance of Gas Detectors for Explosive Atmospheres), emphasizing installation considerations for gas density, airflow direction, ventilation conditions, and explosion-proof ratings.
Common Engineering Pitfalls:
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Installing natural gas detectors near the floor (incorrect; should be near the ceiling).
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Using standard smoke detectors in oily environments (prone to false alarms; prioritize heat detectors or kitchen-specific smoke detectors).
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Ignoring minimum clearance requirements from beams and ducts.
IV. System Integration and Communication Compatibility
Nexisense sensors support multiple industrial communication interfaces:
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RS485 / Modbus RTU: most common, compatible with most PLCs and fire alarm panels.
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LoRaWAN / NB-IoT: suitable for wireless retrofit projects and large campuses.
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4–20 mA: traditional analog input.
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Wireless Mesh: supported by selected models for no-wiring scenarios.
Typical Linkage Solutions:
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Combustible gas alarm → shutoff solenoid valve + start explosion-proof fan + sound & light alarm + upload to fire control room.
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Smoke/heat composite alarm → activate sprinklers or gas fire suppression + fire shutter descent + elevator recall + smoke exhaust fan.
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Multi-detector networking → “two detectors alarm simultaneously” confirmation mechanism to reduce false alarms.
V. Practical Selection Decision Process (Engineering Version)
Does the site have combustible gas leakage risk?
├─ Yes → Prioritize combustible gas detectors (laser/infrared preferred over catalytic)
│ └─ Is it a hazardous area? → Select Ex d / Ex ia rated products
└─ No → Is it a high-temperature, dusty, oily environment unsuitable for smoke detection?
├─ Yes → Prioritize heat detectors (rate-of-rise & fixed-temperature composite)
└─ No → Prioritize photoelectric smoke detectors (high sensitivity, low false alarm)
└─ Need ultra-early warning? → Consider aspirating smoke detection (ASD)
VI. Real Project Application Cases (Simplified)
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An LNG receiving terminal deployed Nexisense TX911-A laser methane detectors with Modbus networking, linking emergency shutoff valves and ventilation systems, achieving <10 s response after leakage and meeting SIL2 safety integrity requirements.
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An underground commercial parking garage retrofit replaced smoke detectors with Nexisense A2-class heat detectors, combined with smoke exhaust linkage, reducing false alarms by over 85%.
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A chemical industrial park deployed a mixed configuration of combustible gas, smoke, and heat detectors, enabling graded alarms and zone isolation, integrated into the park’s SCADA platform.
VII. Frequently Asked Engineering Questions (FAQ)
Q1: Should kitchens use combustible gas detectors or smoke detectors?
A: Combustible gas detectors are mandatory (semiconductor or infrared recommended). Standard smoke detectors are highly prone to false alarms. Kitchen-specific photoelectric smoke detectors may be used as auxiliary devices.
Q2: Why are heat detectors preferred over smoke detectors in underground parking garages?
A: Vehicle exhaust and dust easily cause smoke detector false alarms, while early vehicle fires are dominated by high temperatures, making heat detection faster and more reliable.
Q3: How can false alarms from combustible gas detectors be reduced?
A: Select detectors with strong anti-poisoning and anti-interference capabilities (laser or infrared), set graded alarm thresholds appropriately, and perform regular calibration every 6–12 months.
Q4: Can heat detectors completely replace smoke detectors?
A: No. Heat detectors respond slowly to smoldering fires. Standards require smoke detectors in areas where visible smoke is expected. Combined use is recommended.
Q5: Are wireless solutions reliable in industrial projects?
A: LoRaWAN/NB-IoT perform well in large-area, multi-node scenarios, but signal penetration, battery life, and redundancy must be carefully evaluated.
Q6: How should detector service life be managed?
A: Combustible gas detectors: 3–8 years (depending on type); heat/smoke detectors: 8–10 years. Establish full lifecycle management including calibration records and spare part planning.
Q7: How to integrate with fire alarm panels?
A: Via RS485/Modbus to alarm panels or 4–20 mA to traditional loops. Multi-protocol gateways are recommended for unified management.
Q8: How can new projects comply with the latest explosion-proof and fire standards?
A: Refer to GB/T 20936.2-2024 (gas detectors) and GB 50116-2013 (fire alarm systems), and prioritize products certified with CCC and SIL.
Conclusion
In industrial fire protection system design, combustible gas detectors and heat/smoke detectors are not an “either-or” choice, but rather a scientifically combined solution based on hazard characteristics, environmental conditions, and regulatory requirements. Nexisense sensors provide high reliability, rich communication interfaces, and engineering-grade stability, delivering dependable front-end sensing for system integrators.
If your organization is advancing related projects, you are welcome to contact the Nexisense technical team for site surveys, solution design, sample testing, and integration support. We are committed to being your long-term partner in industrial safety sensing, working together to build safer and smarter industrial environments.
