Gas monitoring for tunnels and underground

The Grand Paris project is a perfect example of the importance of gas detection in tunnels. This massive project, which aims to improve and extend the transport network around Paris, involves the construction of many new tunnels. 

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Five deaths and many serious accidents have occurred since the work began, revealing once again the major safety challenges on the Grand Paris Express construction sites. This underscores the need for gas detection tools, adequate safety devices, and ongoing worker training.

Workers on these sites face high risks, including toxic and explosive gases and confined working conditions. So multigas detectors, monitoring beacons, or self-rescuers like the OXY SR are essential to ensure their safety and prevent serious accidents.

A confined space is an enclosed volume, and the majority of severe or fatal accidents that occur during work in these environments are related to the presence of explosive, toxic, or asphyxiating substances (lack of oxygen). These will be the first risks to be assessed during a work procedure development for safety with devices to detect gaseous emanations in tunnels.

Which gases to monitor in tunnels

Chronic exposure to exhaust gases can lead to considerable neurological disorders (headaches, dizziness, irritability, drowsiness, convulsions), bronchial irritation, and sometimes lung cancer. Therefore, measuring and constantly monitoring the average values (VME) and limit values (VLE) of exposure is imperative for detecting gaseous products in road or rail tunnels:

• Carbon monoxide
• Carbon dioxide
• Nitrogen oxides (nitric oxide and nitrogen dioxide)
• Sulphur dioxide
• Volatile organic compounds (VOC) including benzene
• Oxygen defficiency

Sensors for gaseous substances in tunnels

Multi-gas detector and area monitoring beacon

Regarding personal protection, the multigas detector, like the 4-gas detector, remains the essential PPE. In addition, you can secure one or more work areas with area gas monitors to better define the safety perimeter. For very long tunnels, we recommend communication solutions, as shown below...

LENS Wireless technology

Particularly suited to tunnels, LENS&#; Wireless technology is a new approach to safety on a worksite. With this solution, when a gas detector or area monitoring beacon goes into alarm following a toxic product hazard, a "man in distress" alarm, or a panic situation, all people in the connected group will immediately know about the danger.

&#; More on the LENS Wireless technology

Gas detection - protection for TBM operators

For operations performed in confined spaces, the most commonly used (and least expensive) model is the portable 4-gas detector (explosive gases, O2, CO, and H2S). But if you want to be more relevant for tunnels, you might choose a multi-gas sensor, ideally configured to detect the CO-CO2-NO-NO2-O2 cells present in the atmosphere. Some can monitor up to 6 gases simultaneously. Available in a diffusion version or with a remote sampling pump, this sensor is perfectly suitable to hazardous areas, potentially explosive, toxic, asphyxiating or containing VOCs environments (volatile organic compounds). 

One of the most reliable tunnel work transmitters is Dräger's X-am portable detector. The world's smallest personal monitoring device detects potentially explosive gases and vapors, lack of oxygen, and concentrations of toxic gases. It frequently comes with accessories such as a clip-on pump, sampling hose, and worksite beacon.

To guarantee safe operation, sensors in the tunneling industry need to be checked regularly. Companies equip themselves with a calibration or a bump test station to check that sensor's operation.

Whether in France or Europe, people working in tunnels must wear respiratory protection equipment such as masks and detection devices.

Area gas monitor &#; X-zone

X-am portable multi gas detector

G7 EXO geolocated area gas monitor

Area gas monitor - Radius BZ1

Respiratory protection and self-rescuer mask

Self-rescuing masks, like Ocenco's M20.2, are respiratory protection devices specifically designed for emergency escape in non-breathable, oxygen-poor, highly smoky, or extremely toxic environments where a filtering device would be ineffective or even dangerous. They were originally designed for emergency evacuation in mines, large tunnels, or work in confined spaces. Easy to use, they guarantee worker safety.

The escape hood is specifically well-suited to protect against a fire in a tunnel. It offers 15 minutes' resistance to vapors, particles, and toxic industrial gaseous substances, and enables users to withdraw from the hazardous zone during smoke extraction, for example.

In addition to gas emissions, tunnels are places where fires, flooding, chemical emissions, and collapses can occur. This is why wearing SCBA equipment is not enough. The company in charge of the work must set up a safety perimeter, and an escape route inside the tunnel is essential. The latter must lead to a passageway under the roadway leading to the outside.

Emergency escape breathing device M20.2

Chemical oxygen self-rescuer OXY SR 30 / OXY SR60

Self-rescuer mask &#; SSR 30/100

High autonomy self-rescuer mask &#; EBA 6.5

Demand for ultra-precise and reliable navigation systems has grown, especially in autonomous, aerospace, and industrial applications. There is also recognition that traditional inertial solutions alone are not sufficient for the challenges in far more diverse environments; space, subsea, urban canyons, underground and contested areas.

At the heart of many inertial systems lies the gyroscope, a critical component for maintaining stability, orientation, and accuracy. Our gyroscopes precisely measure rate of turn (°/s) without a fixed reference point. This sets them apart from traditional rotation measurement tools like tachometers or potentiometers. Uniquely, all our gyros use a patented VSG resonating ring technology to detect rotation rate through the Coriolis phenomenon.

Let&#;s explore the key product parameters to help you choose the right gyroscope:

1. Precision and Accuracy:

Whether you need high-precision navigation for a space application, or a simple stabilisation solution for a camera, selecting a gyroscope with the appropriate performance level is crucial. For example, bias instability for our PinPoint® is 12°/hr to 80°/hr and is used in commercial applications. Whereas the CRH03 achieves a comparable DTG and FOG grade performance at <0.03°/hr to 0.1°/hr. This gyro is typically used in challenging environments that require ultra-precise performance.

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2. Environmental:

Will the gyroscope be exposed to extreme temperatures, vibrations, or electromagnetic interference? Opting for a gyroscope with a robust environmental performance ensures reliability and longevity in challenging operating environments. Downhole drilling is a great example of a challenging environment that requires a reliable and robust inertial solution. The CRS39A is a tactical-grade gyro specified to work up to 110°C while delivering an industry-leading low noise performance at 0.006°/s rms.

3. Size and Weight:

Size and weight constraints are often critical factors in inertial, particularly unmanned aerial vehicles (UAVs), and autonomous underwater vehicles (AUVs). It is also important to select a compact and lightweight gyroscope without compromising on performance. Whilst the CRH03 is the perfect solution for these applications, we have developed an OEM version for applications where space and weight are limited.

4. Power Consumption:

For battery-powered devices or applications where energy consumption is a concern, selecting a gyroscope with low power consumption is fundamental. All our gyroscopes benefit from low power consumption, the PinPoint® has a typical consumption at 4mA whereas our highest performing gyros current consumption is still only 30mA.

5. Integration and Compatibility:

Integration with existing systems can play a significant role in choosing a new gyro. Selecting a gyro that interfaces seamlessly with your system architecture, providing the right data output, is crucial for certain applications. All our gyroscopes have an analogue interface, while our PinPoint® is our only gyro that has the flexibility of an analogue and Digital SPI® interface.

Silicon Sensing Solutions:

Now, let&#;s delve into a comparison of all our gyroscopes:

Features: Class-leading bias and noise over temperature, tiny size, available in flat and orthogonal formats, ultra-low power consumption.

Ideal for: Industrial and commercial applications that require a robust and affordable mass-produced gyroscope. Commonly used in attitude sensing, precision navigation, robotics, antenna platform pointing applications that require a miniature footprint, low power consumption and excellent performance over temperature.

Features: FOG-grade performance. Two temperature sensors and MEMS frequency output for precision thermal compensation, it is optimised for low-rate range environments. In-band quiescent noise of 0.03°/s rms and an operating temperature range of &#;10°C to +110°C. This gyro is designed for mounting within a 25mm inside diameter cylinder.

Ideal for: Ultra-high-stability applications in severe environments, such as downhole drilling operations. A cost-effective and extremely rugged alternative to fiber optic and dynamically tuned gyros with significant performance enhancements in critical areas such as bias instability, angle random walk, noise and vibration tolerance.

Features: FOG and DTG comparable bias characteristics. Compact design, providing superior stability performance over time and temperature, the ultimate product where performance in bias instability, angle random walk and low noise are of critical importance.

Ideal for: Space and satellite applications demanding reliability and precision attitude control. Autonomous Vehicles and ROVs, surveying, guidance, avionics and heading control.

Conclusion

Choosing the right gyroscope is an important decision that can significantly impact the performance and reliability for your application. By considering factors such as precision, environmental, size, power consumption, and compatibility, you can make an informed choice tailored to your specific requirements. At Silicon Sensing, we have making gyroscopes for over 25-years. We manage every aspect of our product range in-house, ensuring the highest quality on the market. If you have a question about our products, our highly skilled team provide expert technical support.

Contact us to discuss your requirements of perimeter intrusion detection system. Our experienced sales team can help you identify the options that best suit your needs.