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Welding, Cutting, and Heating (Hot Work) >>

Tunnels and Tunneling

Employees working on tunneling operations are exposed to numerous hazards, including (1) tunnel collapses; (2) hazardous atmospheres; and (3) explosive atmospheres. When employees work in tunnels and in underground chambers of any depth and in shafts exceeding 20 ft. in depth, the following operations are subject to the TSOs:

• Pipe-jacking and boring
  
• Micro-tunneling
  
• Mechanized tunneling
  
• Drill and blast work
  
• Excavation
  
• Ground support work
  
• Repair and maintenance
  
• Tunnel renovations
  

The Mining and Tunneling (M&T) Unit of Cal/OSHA enforces these safety orders, which include:

A. Classifications: The M&T Unit is required to classify the gas hazards of each tunnel. These classi cations are (1) nongassy;
(2) potentially gassy; (3) gassy; and (4) extra hazardous. 8422 (a),(b)

Note: The request for classifi cation must be sent to the nearest M&T Unit office.

B. Pre-job safety conference: Before underground excavation may begin, the M&T Unit must conduct an on-site, pre-job safety conference with the project owner, the general contractor, the tunnel contractor, and the tunnel contractor’s employees. The goal of the conference is to ensure that all of the employees are aware of the conditions under which the tunnel will be driven and that all of the safety issues are discussed and problems resolved. 8408

C. Certified persons: Cal/OSHA requires the persons performing the duties of gas tester or safety representative to be certified by passing a written and an oral examination administered by the M&T Unit. 8406(f),(h)

1. A gas tester is required for the following operations:
   
   1. All classifications other than non-gassy
      
   2. Projects during which diesel equipment is used underground
      
   3. Hazardous underground gas conditions. 8470
      
2. A safety representative must direct the required safety and health program and must be on-site while employees are engaged in operations during which the TSOs apply. 8406(f)
   The safety representative must have knowledge in underground safety, must be able to recognize hazards, and must have the authority to correct unsafe conditions and procedures subject to the TSOs. 8406(f)
   

D. Diesel engines: Diesel engines are the only type of internal combustion engine acceptable for use during tunneling operations, provided that the following requirements are met:

1. Cal/OSHA must issue a permit for engine operation.
   
2. Conditions of the permit must be observed.
   
3. Ventilation and fresh air flow must meet the required minimum standards.
   
4. Air concentrations of nitrogen dioxide, carbon monoxide, and carbon dioxide in the tunnel must be determined at least once during each shift at the peak of diesel operation and kept at or below the PELs.
   
5. A written record must be kept of the above readings.
   
6. PELs of the above air contaminants or any other contaminants must not be exceeded.
   
7. A certified gas tester must conduct the testing (see additional requirements in 8470).
   
8. An approved exhaust purifier must be installed and maintained (see the requirements in 8470).
   

E. Licensed blasters: All blasting at tunnel sites shall be carried out or directed by California licensed blasters as required by TSO 8560.