Mining Publication: Doing the Math: The Effectiveness of Enclosed-Cab Air-Cleaning Methods Can Be Spelled Out in Mathematical Equations

Enclosed cabs are a primary means of reducing equipment operator's silica dust exposure at surface mines. The National Institute of Occupational Safety and Health The various factors evaluated were intake filter efficiency, intake air leakage, intake filter loading, wind infiltration, use of a recirculation filter, and the use of an intake pressurization fan. The result of this laboratory testing has shown that the two most important factors for an effective filtration system on an enclosed cab were the efficiency of the intake filter and the use of a recirculation filter. A higher-efficiency intake filter considerably increased the quality of the intake air that was delivered into the enclosed cab. It also was determined that air leakage around the intake filter noticeably reduced its air cleaning effectiveness. The second key factor is the use of a recirculation filter, which was shown to improve the air quality in the enclosed cab by six to 12.7 times more than the intake filter alone. The reason for the significant improvement was that the cab air was constantly drawn through the recirculation filter, thus continually filtering the dust out of the air. These cab protection factor calculations represent operating conditions at steady-state conditions within a sealed, pressurized cab (doors and windows closed). Actual cab protection factors over a working shift will vary below this calculated value, depending on the frequency and time that the operator opens the cab door and windows. Therefore, keeping the cab tightly sealed and pressurized is a key aspect in achieving the highest protection factor for an operator. The higher the protection factor achieved on a cab reduces the operator's exposure to the outside dust. Finally, an effective cab filtration system reduces the dust and dirt that infiltrates the HVAC system, increasing its thermal effectiveness and reducing wear on its internal components.