Understanding CO and NOx Accumulation in Underground Environments
Tunnels, subway systems, underground parking, and utility corridors present unique challenges in **air quality management**. Unlike open environments, these confined spaces trap gases such as carbon monoxide (CO) and nitrogen oxides (NOx) due to limited natural ventilation and high vehicle or equipment emissions. Over time, even low-level accumulation can reach dangerous thresholds, posing serious health and safety risks to workers and the public.
Effective **long-term monitoring** is not optional—it is a regulatory and operational necessity. Without continuous data collection and real-time analysis, ventilation systems operate blindly, leading to either energy waste or hazardous conditions. The solution lies in integrating intelligent gas detection networks with automated control systems.
The Role of Advanced Gas Detection Systems
A robust gas detection strategy must account for multiple gas types, environmental variability, and long-term reliability. Traditional point detectors often fail under high humidity, temperature fluctuations, or dust exposure—common in tunnel environments. Modern systems, such as those offered by Shanghai Gewei Electronic Safety Equipment Co., Ltd., utilize **infrared and laser-based sensing technologies** to overcome these limitations.
The GDE series, for example, employs high-precision infrared sensors with automatic temperature compensation and zero-point calibration. These features ensure stable performance across a wide temperature range (-40°C to 70°C), making them ideal for deep tunnels and underground utility vaults where thermal gradients are significant.
Sensor Technology Selection: Matching Principle to Application
Selecting the correct detection principle is critical. In underground spaces, **infrared (IR) sensors** are preferred for combustible gases due to their immunity to poisoning, long lifespan (>5 years), and minimal drift. For toxic gases like CO and NOx, **electrochemical sensors** are more appropriate, offering high selectivity and low detection limits (typically in ppm range).
The GDC series supports interchangeable sensor modules, allowing operators to deploy catalytic, infrared, or semiconductor sensors based on the dominant gas hazard. This modularity enables future-proofing and reduces total cost of ownership through pre-calibrated smart plug-in sensors that minimize downtime during replacement.
System Integration and Data Transmission
Standalone detectors are insufficient for large-scale tunnel networks. A comprehensive solution requires seamless integration into a centralized control architecture. The GDC and GDA series support 4-20mA analog output, RS485 Modbus, and relay outputs, enabling direct connection to PLCs, SCADA systems, or building management platforms.
For remote monitoring, Gewei’s IoT-enabled gas detectors can be paired with 4G/WiFi modules and linked to the company’s proprietary cloud platform. This setup allows real-time data logging, historical trend analysis, and mobile alerts—critical for maintenance teams managing multiple tunnel segments across a city.
Ventilation Control: From Reactive to Predictive
Ventilation is the primary method of mitigating gas accumulation, but fixed-speed fans are inefficient and costly. A smarter approach uses **closed-loop control** driven by real-time gas concentration data. When CO levels exceed 30 ppm or NOx surpasses 5 ppm, the system automatically activates exhaust fans at variable speeds, adjusting airflow based on actual demand rather than time-based schedules.
The GM810/GM820 gas alarm controllers serve as the brain of this system. With modular design, automatic bus addressing, and built-in circuit protection, they support up to 256 detectors per unit and can trigger cascading responses—such as activating emergency lighting, closing dampers, or sending alerts to mobile devices via the cloud.
Reliability and Safety Certification
Underground installations demand equipment with proven durability and compliance. All Gewei detectors are certified for use in hazardous areas (Zone 1 and Zone 2), featuring explosion-proof (Ex d IIC T6 Gb) and dust ignition-proof (DIP A20 TA T6) enclosures. The IP66 rating ensures protection against water ingress, essential for tunnels exposed to condensation or washdowns.
Each unit undergoes rigorous testing for electromagnetic compatibility (GB16838), ensuring stable operation even in high-noise electrical environments common in power tunnels and metro systems.
Long-Term Maintenance and System Longevity
A well-designed monitoring system reduces maintenance burden. Gewei’s **zero-drift compensation** and self-diagnostic features allow for extended calibration intervals—up to 6 months for infrared sensors—while maintaining measurement accuracy within ±3% FS.
The inclusion of color LED displays (visible up to 25 meters) and non-intrusive infrared remote control eliminates the need for physical access during routine checks, minimizing disruption in operational tunnels.
For critical infrastructure projects, the combination of multi-sensor fusion, cloud-based analytics, and automated ventilation control represents the next generation of underground safety management. Shanghai Gewei’s integrated ecosystem—from flame detection to gas detection systems and IoT connectivity—provides a scalable, future-ready solution for long-term CO/NOx monitoring in any underground environment.