Investigation of induced recirculation during planned ventilation system maintenance

Area of Science:

• Mining Engineering
• Occupational Health and Safety
• Environmental Science

Background:

• Increasing mine airflow is crucial for underground metal/nonmetal (M/NM) mine worker health and safety.
• Controlled recirculation offers a viable solution for enhancing airflow when increasing overall mine ventilation capacity is not feasible.
• This method involves reusing a portion of return air to supplement intake air, improving contaminant dilution and airflow velocity.

Purpose of the Study:

• To investigate the effects of controlled recirculation on mine ventilation systems and worker exposure during reduced primary airflow conditions.
• To evaluate the impact of controlled recirculation on airflow distribution, contaminant levels, and miner health in an underground M/NM mine.
• To provide data for better planning and implementation of recirculation strategies in M/NM mine ventilation.

Main Methods:

• Field investigation at a Nevada gold mine undergoing shaft rehabilitation with reduced main fan operation.
• Monitoring of ventilation districts under normal operation and during induced controlled recirculation scenarios.
• Measurement of airflow rates, total dust, respirable dust, and diesel particulate matter (DPM) to assess exposure levels.

Main Results:

• Nineteen percent controlled recirculation resulted in no significant change in overall district airflow distribution but a slight decrease in fresh air intake.
• Total and respirable dust levels increased modestly, remaining within acceptable limits.
• Diesel particulate matter (DPM) mass flow increased, yet miner exposure levels showed only minor increases relative to the recirculation percentage.

Conclusions:

• Controlled recirculation can be an effective strategy to maintain airflow and dilute contaminants in M/NM mines, even during periods of reduced primary ventilation.
• While DPM mass flow increased, direct miner exposure levels were minimally affected, suggesting that ventilation modeling incorporating DPM mass flow rates can aid in planning recirculation.
• Proper implementation and monitoring are essential to ensure the health and safety benefits of controlled recirculation in underground mining environments.