THE COHEN GROUP
  Environmental Health & Safety Consulting Services

The Cohen Group Newsletter - Volume 18  Issue 2, Article 5.  May 2007

 Gas Testing in Tunneling and Mining
By Dustin Christensen

Despite advances in knowledge and safety regulations workers in tunnels and mines are at risk of injury due to the possibility of the presence of hazardous gases.  In order to help protect these workers Cal/OSHA has requirements for air testing and ventilation in tunnels and mines.

For work being done in the areas of tunnel construction, pipejacking, boring, pipeline operations or mining meeting certain criteria, Cal/OSHA requires a Certified Gas Tester to be present on the job site.  The criteria for tunnels with a diameter of 30 inches and over are set out in Tunnel Safety Orders T8CCR 8424(a) which states that tunnels that contain or are suspected of containing dangerous airborne contaminants shall be tested before employees begin to work in the tunnel.  The tests must be made by a person who has been certified by Cal/OSHA.  Similar regulations are made in Mine Safety Orders, T8CCR 7104(c).

 Dangerous airborne contaminants may include flammable gas mixtures, gases that cause adverse health effects or contaminants that cause the oxygen concentration in the tunnel to be greater than 22% or below 19.5%.  Tunnels may be classified according to the concentration of flammable gas compared to the gas’ lowest concentration that could result in an explosion.  If a flammable gas mixture reaches 20% of its’ lower explosive limit all persons must be removed from the tunnel until re-entry has been authorized by Cal/OSHA.

Proper ventilation must be maintained in tunnels to ensure that persons are not exposed to dust, vapors, and gases above the permissible exposure limits listed in Table AC-1 of the California General Industry Safety Orders.  During dust-producing activities in tunnels up to 30 feet in diameter, a minimum ventilation velocity of 60 feet per minute must be maintained.  A ventilation velocity of 30 feet per minute is required in tunnels with diameters of 30 feet or larger.  The airflow may need to be increased to ensure that each person receives 200 cubic feet per minute of fresh air or that an additional 100 cubic feet per minute of fresh air is supplied for each braking horsepower of diesel equipment being operated. 

Through proper air testing and ventilation, dangers to workers in tunnels and mines can be greatly reduced.  If your worksite requires a Cal/OSHA certified gas tester or have any questions contact The Cohen Group.