The No. 3 mine was a low coal mine, with a seam height averaging 21 to 24 inches.  The mine featured one working section consisting of a series of entries with connecting crosscuts.  However, the No. 1 Right entry and the intersecting No. 9 Right crosscut had both been mined excessively to the right of center, and the No. 8 crosscut had been mined excessively to the left of center.

Because of these deviations, the No. 9 and No. 8 entries did not - as stipulated in the mine plan - parallel one another; instead they formed an acute angle.

At about 12:30 p.m. on July 31, the section foreman delivered two cases of explosives to the shot firer.  The shot firer used some of these explosives for routine production blasting in the 3-way faces in the No. 1 Right entry crosscuts.

Operations continued normally until about 2:00 p.m., when an explosion occurred.  Three miners who had been working in the No. 8 crosscut were instantly killed; two others were hospitalized for smoke inhalation, and another avoided injury.

MSHA investigators determined that management had failed to ensure that entries and crosscuts were mined in the proper direction and alignment.  As a result, the No. 8 and 9 crosscuts drifted, reducing the thickness of the coal pillar separating them.

In addition, explosives, detonators, and miners were directly aligned with explosive forces from the production blasting conducted in the right crosscut of the No. 1 Right entry.  These forces penetrated the coal pillar, and detonated the unused explosives located near the victims.

Source:
	Historical Summary of Mine Disasters in the United States - Volume II