About one-half of all continuous mining faces in the United States are using extended cutting, i.e., advancing more than 20 ft past the last row of bolts. Most of these extended-cut approvals are for cutting depths of approximately 40 ft. Almost all of the continuous miners on these faces are equipped with machine mounted dust scrubbers and water spray systems for dust control. Little is known about ow much ventilation air reaches the box-cut face during various parts of the cutting sequence. This is of particular concern when a 40-ft, two-pass, extended cut is taken, because at the start of the 40-ft slab cut, the continuous miner is located 40 ft from the point of deepest penetration-the face of the 40-ft box cut. NIOSH, Pittsburgh Research Laboratory, undertook a study to evaluate this situation.