Understanding Hazardous Area Classifications and Their Direct Impact on Detector Placement
Hazardous area classification—whether based on Zone (IECEx/ATEX) or Division (NEC/NFPA) systems—forms the foundation for determining where and how gas and flame detectors should be installed. These classifications define the likelihood, duration, and type of hazardous atmosphere present in a given space, directly influencing detector selection, positioning, and performance requirements.
Zone vs. Division: Key Differences in Classification Systems
The Zone system (IEC 60079) divides hazardous areas into three zones based on frequency and duration of explosive atmospheres:
- Zone 0: Continuous presence of explosive gas-air mixtures (≥1000 hours/year)
- Zone 1: Likely presence during normal operation (10–1000 hours/year)
- Zone 2: Unlikely during normal operation, short duration if present (<10 hours/year)
In contrast, the Division system (NFPA 70/NEC 500) uses two divisions:
- Division 1: Ignitable concentration likely under normal or abnormal conditions
- Division 2: Ignitable concentration only under fault conditions
These distinctions are not merely academic—they dictate equipment certification, enclosure types, and detector placement density. For example, Zone 0 demands intrinsically safe or flameproof equipment with redundant detection, while Division 2 may allow standard industrial detectors with lower coverage density.
Detector Placement: From Classification to Practical Layout
Detector placement is governed by three core principles: gas dispersion behavior, equipment risk profile, and classification severity.
In Zone 1 or Division 1 areas, detectors must be placed near potential leak sources—valves, flanges, pumps, and compressors. The minimum detection radius is typically 3–5 meters, but this varies by gas density. For example, methane (lighter than air) accumulates at ceiling level, requiring top-mounted detectors, while propane (heavier than air) pools near the floor, necessitating low-level placement.
For toxic gases like H₂S or CO, detectors must be located at breathing height (1.2–1.8 meters) to protect personnel. In contrast, flame detectors should be positioned with unobstructed line-of-sight to ignition-prone zones, accounting for blind spots caused by equipment layout.
Sensor Technology Selection Based on Classification and Environment
The classification also determines the appropriate gas detection principle. In high-risk zones (Zone 0/1, Division 1), infrared (IR) and laser-based sensors are preferred due to their long lifespan (>5 years), immunity to poisoning, and high accuracy (±3%FS). These are ideal for GDE series detectors from Shanghai Gewei Electronics, which utilize IR/laser sensors with automatic temperature compensation and zero drift correction, ensuring stable performance in fluctuating industrial environments.
In Division 2 or Zone 2 areas, catalytic combustion and electrochemical sensors offer cost-effective solutions. The GDC series supports interchangeable sensor modules—including catalytic, IR, and semiconductor types—enabling flexible deployment across mixed-risk facilities. For example, a refinery may use IR sensors near distillation columns (Zone 1) and catalytic sensors in storage yards (Zone 2), all managed through a unified gas detection system.
Integration with Control Systems and IoT Platforms
Modern hazardous area monitoring requires more than standalone detectors. The GM810/GM820 gas alarm controllers from Gewei Electronics provide centralized monitoring with modular expansion, supporting up to 128 detectors via RS485 or 4G/WiFi connectivity. These controllers integrate seamlessly with cloud-based IoT platforms, enabling real-time data logging, remote diagnostics, and predictive maintenance alerts.
For flame detection, Gewei’s UV/IR and multi-spectrum flame detectors combine AI-powered analysis with wide-angle coverage (up to 120°), reducing blind spots in complex layouts. When integrated with the cloud platform, operators receive instant notifications on mobile clients, including location, gas type, and concentration trends.
Compliance, Calibration, and Maintenance in Classified Areas
Detectors in hazardous areas must meet strict certification standards: Ex d IIC T6 Gb (flameproof), Ex ia (intrinsic safety), or IP66 (dust/water resistance). The GDA series detectors, designed for 1/2 zones, feature dust explosion-proof certification and CPA metering licenses, ensuring compliance with GB15322 and GB3836 standards.
Regular calibration is critical. Gewei’s smart plug-and-play sensors support pre-calibration, minimizing downtime. The automatic zero calibration function adjusts for environmental drift, maintaining accuracy over time. In Zone 0 applications, redundant detection with dual sensors (e.g., IR + catalytic) is recommended to ensure fail-safe operation.
Case Application: Petrochemical Facility Layout
In a typical petrochemical plant:
- Zone 1 (process units): GDE820 IR detectors placed at 5-meter intervals near reactors and compressors
- Zone 2 (storage tanks): GDC810 catalytic detectors installed at tank vents and pump bases
- Flame detection: UV/IR flame detectors mounted on elevated platforms with 360° coverage
- Control room: GM820 controller with 4G module for remote access and alarm escalation
This configuration ensures full compliance with IEC 60079 and NFPA 70, while leveraging Gewei’s integrated detection ecosystem for scalability and reliability.