Underground Face Airflow, Velocity, and Diesel Dilution

Which is why a velocity check can pass while the air is short. Enough velocity to sweep the face, enough volume to dilute diesel exhaust for every machine working there, enough to clear blast fumes in the required re-entry time, and enough to control dust and any gas the strata make. Diesel dilution is very often the governing one, because the required air per unit of engine power is large and it is ADDITIVE across machines. An 18 by 14 ft heading is 252 sq ft, and a fan rated 25,000 cfm delivering 70% through the tubing puts 17,500 cfm at the face -- 69 fpm, comfortably over a 60 fpm sweep minimum. Then check the diesel: a loader and a haul truck at 10,000 cfm each need 20,000, and the heading has 17,500. THE VELOCITY CHECK PASSED AND THE HEADING IS STILL SHORT. The number that gets missed is TUBING LEAKAGE, and it is the fixable part. Twenty-five thousand at the fan and seventeen and a half at the face means 7,500 cfm is going out through the couplings. Bring tubing efficiency to 80% and the heading clears the diesel requirement with no new fan and no new tubing -- couplings and repairs. That is a maintenance job a measurement at the FACE identifies and a measurement at the fan never will, and measuring at the face is the discipline this supports. The tubing end setback matters as much as the quantity: air discharged too far back short-circuits and returns along the heading, leaving a dead zone exactly where people work. A comparison of delivered airflow against requirements the user supplies. It does not calculate tubing leakage, pressure loss, or fan selection, and it does not determine the required diesel ventilation rate, which is set by regulation per unit of engine power and differs between MSHA metal and nonmetal, MSHA coal, and other jurisdictions. It does not evaluate methane or other strata gas, which in gassy mines governs everything and carries its own statutory limits and monitoring, and it does not evaluate radon, silica, or diesel particulate exposure, which are health standards with their own sampling requirements. Underground ventilation is a regulated, engineered system: the mine ventilation plan, the ventilation engineer, and MSHA govern.

heading area = width x height; delivered airflow = fan rating x tubing efficiency; face velocity = delivered / area; the governing requirement is the LARGER of area x minimum sweep velocity and the summed diesel dilution demand.

The face-velocity relation and the additive diesel dilution requirement by name, with the required air per unit of engine power entered because it is set by regulation and differs between jurisdictions. The mine ventilation plan, the ventilation engineer, and MSHA govern.

Division and comparison on the user's own heading and equipment data; no regulatory rate table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: heading_width_ft, heading_height_ft, fan_airflow_cfm, tubing_efficiency_pct, diesel_units, diesel_cfm_each, min_face_velocity_fpm, heading_area_sqft, delivered_cfm, leakage_cfm, face_velocity_fpm, diesel_required_cfm, governing_cfm, efficiency_needed_pct

• Diesel dilution usually governs the rate per unit of engine power is large and it adds across machinesMSHA ventilation requirements
• Measure at the FACE, not the fan the gap between them is tubing leakage and it is a maintenance findingmine ventilation practice
• Tubing setback creates a dead zone air discharged too far back short-circuits and never reaches the facemine ventilation plan