The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) conducted joint research to evaluate explosion blast effects on typical U.S. mine ventilation stoppings in the NIOSH Pittsburgh Research Laboratory's (PRL) Lake Lynn Experimental Mine (LLEM). An innovative Australian-designed brattice stopping was also evaluated. After mine explosion accidents, MSHA conducts investigations to determine the cause(s) as a means to prevent future occurrences. As part of these postexplosion investigations, the condition of underground stoppings, including the debris from damaged stoppings, is documented as evidence of the approximate strength and the direction of the explosion forces. Permanent stoppings are used to control and direct the ventilation airflow through underground coal mines to dilute and render harmless methane, entrained coal dust, and other contaminants at the working face and other areas of the mine. 30 CFR 75.333 requires that permanent stoppings be built and maintained between intake and return air courses beginning at the third connecting crosscut outby the working face and to separate other air courses and direct air as specified. To perform the intended function and meet the requirements of 30 CFR 75.333, permanent stoppings are to be constructed in a traditionally accepted method and of materials that have been demonstrated to perform adequately or in a method and of materials that have been tested and shown to have a minimum strength equal to or greater than the traditionally accepted in-mine controls. A few examples of traditionally accepted 61 Fed. Reg. 9764 (1996)] stopping construction methods are as follows: (1) 8-in (20-cm) and 6-in (15-cm) concrete block (both hollow-core and solid) with mortared joints, (2) 8-in (20-cm) and 6-in (15-cm) concrete blocks, dry-stacked and coated on one or both sides with a strength-enhancing sealant suitable for dry-stacked stoppings, and (3) steel stoppings (minimum 20-gauge) with seams and perimeter sealed with a suitable mine sealant. Unlike mine ventilation seal structures that are commonly used to isolate unused sections of the mine, stoppings are not intended to withstand explosion overpressures. Unfortunately, mine explosions do occur. Depending on the location and severity, explosions can result in fatalities and injuries to underground mining personnel and cause considerable underground damage to equipment and structures. In the mine explosions in Alabama in 2001 and West Virginia in 2006, ventilation stoppings were destroyed. Mine Safety and Health Administration (MSHA) personnel conduct investigations into these types of explosion accidents to determine the root cause(s) as a means to prevent future occurrences. As part of postexplosion investigations, the location and condition of underground ventilation structures and debris are mapped. This information helps the investigators determine the strength and the direction of the forces of the explosion.