The National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Research Laboratory, (PRL) participated with Barclay Mowlem Construction Ltd. of Queensland, Australia in a joint research program to evaluate the strength characteristics and air-leakage of four seal and two stopping designs and one overcast design for use in underground coal mines. A fundamental safety research area for NIOSH is to eliminate the occurrences of coal mine explosions or to mitigate their effects. One approach to achieve this goal is to develop and/or evaluate new and innovative seal designs that provide increased explosion isolation protection for the mining personnel against ignitions which originate from within the gob or other worked out areas of the mine. Full-scale seals, stoppings, and an overcast were constructed in the PRL's Lake Lynn laboratory experimental mine located near Fairchance, Fayette County, Pennsylvania. Each of the seal designs and the overcast side and wing walls utilized one or more air inflated vinyl bladder assemblies anchored to the mine roof and hitched into the ribs and floor. The air within these bladders was then displaced with a high strength cementitious grout. The overcast deck consisted of a 20-mm-thick reinforced cementitious slab. The grout filled vinyl bladder and surrounding strata were then coated with a gunite material on all exposed surfaces of the overcast and on the intake side of the seals. This was the first time an overcast structure had been explosion tested under full-scale conditions. One stopping design, referred to as a quickseal, consisted of a vinyl bladder inflated with air. The purpose of the test was to determine if the inflated bladder could withstand the explosion pressure pulse without rupturing. The second stopping design consisted of a series of 170-mm diameter water -filled tubes which were joined together to form a full width curtain. The individual tubes of this stopping were designed to release to vent the explosion pressure and then return to their original positions to serve again as a ventilation control device. All of the seals and stoppings and the overcast design passed the air-leakage tests prior to being subjected to a series of explosions with static pressure pulses ranging from 14 to 475 kPa (2 to 69 psi). Instrumentation measured seal and overcast wall displacement as a function of time, providing data to assist in the development of numerical models for future design. The air-inflated vinyl bladder of the quick seal stopping design did not rupture when subjected to a 14-kPa (2.0-psi) static pressure pulse. The individual tubes of water stopping released as planned and returned to their original position, but the 19-kPa (2.8 psi) static pressure pulse from the explosion caused the base of each tube to rupture resulting in a complete loss of water. The 450-mm-thick seal design in the 2.8-m-high third crosscut withstood an explosion pressure of 170-kPa (25 psi), but failed during a subsequent test which generated a peak static pressure of 475 kPa (69 psi) at the seal location. A similar 450-mm-thick seal in the 2.1-m -high second crosscut withstood three higher level explosion tests which generated peak static pressures of 195, 205, and 370 kPa (28, 30, and 54 psi) at the seal location. Next, the overcast design withstood four explosions which generated static overpressures ranging from 16 to 47 kPa (2.3 to 6.8 psi). Finally, two more seals, consisting of a series of attached grout filled vinyl tubes, were evaluated in the third and fourth crosscuts. the 240-mm-thick seal design in the 2.8-m-high third crosscut failed when subjected to a 160-kPa (23-psi) explosion pressure approximately 24 h after its installation. the 165-mm-thick seal design also failed against a static pressure pulse of 115 kPa (17 psi) at the fourth crosscut.