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. 

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.

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

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...

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

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 5000 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.

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.