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Combustible Gas Detectors vs. Heat/Smoke Detectors in Detail: 2024 Industrial Fire Protection System Selection and Integration Guide
In industrial sites, commercial complexes, energy facilities, petrochemical projects, and other fields, fire and explosion risk prevention and control have become a core component of system integration projects. Selecting appropriate detection front-end equipment for different hazard sources directly determines the response timeliness, false alarm suppression capability, and compatibility with BMS, SCADA, PLC, and other platforms of the entire fire alarm and linkage system.
Nexisense, as a supplier specializing in industrial-grade sensors, offers a series of modules including laser methane, infrared combustible gas, heat, and photoelectric smoke detectors, widely used in system integrator and general engineering contracting projects. This article, from an engineering perspective, systematically compares combustible gas detectors with heat/smoke detectors, focusing on technical selection, installation specifications, communication interfaces, linkage strategies, and actual project implementation experience, providing references for project design and procurement in 2024-2025.
1. Core Functions and Hazard Prevention Positioning Comparison
| Device Type | Core Monitoring Object | Main Prevention Target | Typical Engineering Application Scenarios | Priority Scenarios (System Integration Perspective) |
|---|---|---|---|---|
| Combustible Gas Detector | Methane, propane, hydrogen and other combustible gas concentrations | Prevent leakage → explosion accidents | Gas boiler rooms, chemical plants, LNG filling stations, oil and gas pipeline rooms | Explosion-proof zones (Zone 1/2) with risk of explosive gas accumulation |
| Heat Detector | Abnormal increase in ambient temperature or rate of temperature rise | Early warning in the high-temperature stage of fire development | Underground garages, drying workshops, power distribution rooms, cable interlayers | Environments with low smoke, high dust, high-temperature steam |
| Smoke Detector | Smoke particles in the early stage of combustion (smoldering/flaming) | Early warning of fire (smoldering stage) | Office areas, hotel rooms, archives, clean workshops | Conventional civil/commercial buildings, locations where obvious smoke is generated in the early stage |
Essential Differences Summary
Combustible gas detectors are pre-prevention devices, aimed at interrupting the initial link of the explosion chain (gas accumulation → ignition source).
Heat/smoke detectors are in-process warning devices, providing alarm signals when a fire has already occurred or is about to develop.
In large-scale projects, a “combustible gas detector + smoke/heat composite” strategy is usually adopted to form a multi-level risk prevention and control system.
2. Technical Principles and Performance Parameter Comparison
1. Combustible Gas Detector
Mainstream detection principles (Nexisense mainstream product line):
Laser Absorption Spectroscopy (TDLAS): such as TX911-A series, targeted at specific gases like methane, strong resistance to cross-interference, long lifespan (>10 years), suitable for long-distance pipeline monitoring.
Infrared Absorption: such as TX721-A1B low-power series, broad-spectrum detection of various hydrocarbon gases, strong resistance to poisoning and poisoning recovery.
Catalytic Combustion: traditional industrial mainstream, fast response, but requires regular calibration, susceptible to poisoning by silicones and sulfides.
Key trigger thresholds: usually graded alarms at 10%-50% LEL, typical first-level alarm set at 10%-20% LEL (for example, methane 5% vol = 100% LEL, then 0.5%-1% vol triggers).
Response time: catalytic/infrared type<10-15s, laser type <5s (depending on optical path).
2. Heat Detector
Fixed Temperature Type: triggers when ambient temperature reaches fixed thresholds such as 57℃/70℃/90℃ (common A2, B classes).
Differential Temperature Type: triggers when temperature rise rate >5-10℃/min.
Differential-Fixed Temperature Composite Type: combines both characteristics to improve response reliability.
Application limitations: slower response to slow-rising temperature fires (such as cable overload).
3. Smoke Detector
Photoelectric Type (current mainstream): utilizes the scattering/obstruction principle of smoke on infrared light, high sensitivity, excellent response to smoldering fires.
Ionization Type: gradually phased out (environmental and false alarm issues).
Response time: 30-90s in smoldering stage, faster in flaming stage.
3. Installation Location and Engineering Specification Requirements (2024 Latest Reference)
| Item | Combustible Gas Detector | Heat Detector | Smoke Detector | Main Reference Standard |
|---|---|---|---|---|
| Installation Height | Lighter-than-air gases (methane, hydrogen): near ceiling; heavier-than-air gases (LPG): 0.3-0.6m from floor | ≤0.3m below ceiling | Center of ceiling or highest point | GB 15322 series / GB 50116-2013 |
| Distance from Leakage Source/Risk Point | Horizontal distance from gas appliance/valve ≤4m | — | — | GB 15322.1-2019 and subsequent revisions |
| Protected Area/Spacing | Depending on site diffusion model, generally 8-12㎡ per unit | Depending on type, common 50-80㎡ per unit | 60-100㎡ per unit (ceiling height<6m) | GB 50116 Appendix E |
| Avoid Interference Sources | Avoid direct blowing of oil fume and steam; keep away from exhaust outlets | Avoid air conditioning outlets ≥1.5m | Avoid kitchen oil fume, 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 that detector installation must consider gas density, airflow direction, ventilation conditions, and explosion-proof rating.
Common Engineering Misconceptions:
Installing natural gas detectors on the floor (incorrect, should be near the ceiling).
Using ordinary smoke detectors in oily fume environments (prone to false alarms, priority should be given to heat or special kitchen-type photoelectric smoke detectors).
Ignoring the minimum spacing requirements between detectors and beams, air ducts.
4. System Integration and Communication Compatibility Focus
Nexisense series sensors support multiple industrial communication interfaces for easy integration:
RS485 / Modbus RTU: most common, compatible with most PLCs and fire alarm hosts.
LoRaWAN / NB-IoT: suitable for wireless renovation projects and large campuses.
4-20mA: traditional analog input.
Wireless Mesh: some models supported, suitable for no-wiring scenarios.
Typical Linkage Schemes:
Combustible gas detector alarm → shut off solenoid valve + start explosion-proof fan + sound and light alarm + upload to fire control room.
Smoke/heat composite alarm → start sprinkler/gas fire extinguishing + fire shutter descent + elevator forced landing + smoke exhaust fan.
Multi-detector networking → adopt “two same-type detectors alarming simultaneously” confirmation mechanism to reduce false alarms.
5. Selection Decision Flow (Practical Engineering Project Version)
Does the project site have combustible gas leakage risk?
├─ Yes ──> Prioritize combustible gas detector (laser/infrared preferred over catalytic combustion)
│ └─ Is it an explosion-proof zone? ──> Select Ex d / Ex ia level products
└─ No Is it a high-temperature, dust, oil fume or other environment unsuitable for smoke detection?
├─ Yes ──> Prioritize heat detector (differential-fixed temperature composite type)
└─ No ──> Prioritize photoelectric smoke detector (high sensitivity, low false alarm type)
└─ Need ultra-early warning? ──> Consider aspirating smoke detection (ASD)
6. Real Project Application Cases (Simplified Version)
A certain LNG receiving station project deployed Nexisense TX911-A laser methane detectors + Modbus networking, linked with emergency shut-off valves and ventilation systems, achieving<10s response after leakage, meeting SIL2 safety integrity level requirements.
Underground commercial garage renovation: original smoke detectors had high false alarm rate, replaced with Nexisense heat detectors (A2 class), combined with smoke exhaust linkage, false alarms reduced by more than 85%.
Chemical park comprehensive monitoring: mixed deployment of combustible gas + smoke + heat, achieving graded alarms and area isolation, connected to the park SCADA platform.
7. Common Engineering Problem FAQ
Q1: Should combustible gas detectors or smoke detectors be installed in kitchen areas?
A: Combustible gas detectors must be installed (semiconductor or infrared type recommended), ordinary smoke detectors are extremely prone to false alarms from oil fume. Kitchen-specific photoelectric smoke detectors can be used as auxiliary.
Q2: Why prioritize heat detectors over smoke detectors in underground garages?
A: Vehicle exhaust and dust easily cause false alarms in smoke detectors, while vehicle spontaneous combustion starts with high temperature, making heat detectors respond faster and more reliably.
Q3: How to reduce the false alarm rate of combustible gas detectors?
A: Choose sensors with strong anti-poisoning and anti-interference capabilities (such as laser/infrared), reasonably set graded alarm thresholds, 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. Specifications require priority for smoke detectors in places with obvious smoke; the two are often used in combination.
Q5: Are wireless solutions reliable in industrial projects?
A: LoRaWAN/NB-IoT performs well in wide coverage and multi-node scenarios, but signal penetration, battery life, and redundancy design need to be evaluated.
Q6: How to manage detector lifespan?
A: Combustible gas 3-8 years (depending on type), heat/smoke 8-10 years. It is recommended to establish full lifecycle management, including calibration records and spare parts planning.
Q7: How to link with fire alarm host?
A: Access alarm host via RS485/Modbus, or traditional loop via 4-20mA. It is recommended to use multi-protocol gateways for unified management.
Q8: How to meet the latest explosion-proof/fire regulations for new projects?
A: Refer to GB/T 20936.2-2024 (Gas Detectors), GB 50116-2013 (Fire Alarm Systems), prioritize products with CCC and SIL certification.
Conclusion
In industrial fire protection system design, combustible gas detectors and heat/smoke detectors are not simply an “either-or” choice, but a scientific combination based on hazard source characteristics, environmental conditions, and specification requirements. The Nexisense series sensors provide reliable front-end perception capabilities for system integrators with high reliability, rich interfaces, and engineering-grade stability.
If your company is advancing related projects, welcome to contact the Nexisense technical team for on-site survey, solution design, sample testing, and integration support. We are committed to becoming your long-term partner in the field of industrial safety perception, jointly building a safer and smarter industrial environment.
