Results are pending in an underground test blast set off Wednesday in Fayette County, the fourth of a series of blasts to determine why a mine seal failed at West Virginia's Sago mine on Jan. 2, leading to the deaths of 12 miners.

The seals, including ones made of Omega Block similar to those at Sago, withstood a test blast Aug. 4 that reportedly had a force of less than 20 pounds per square inch, or psi. This week's test increased the explosive force, although it was not immediately known by how much.

The seals are used to block off a portion of a mine and, until recently, were supposed to be built to withstand a 20 psi force. Following the Sago disaster and the deaths of five miners in Kentucky in May -- both involving the ignition of methane gas -- federal officials have increased the standard to 50 psi.

West Virginia mining officials also have placed a moratorium on seals constructed with the lightweight, dense foam Omega Blocks, and federal officials have placed tighter restrictions on their use.

The tests are being done at the Lake Lynn Laboratory experimental mine near Fairchance.

No public information on the test results is being released by officials at the U.S. Mine Safety and Health Administration, which is conducting the test blast series in conjunction with the National Institute for Occupational Safety and Health and West Virginia Office of Miners' Health, Safety and Training.

The tests are expected to continue through the summer as part of MSHA's investigation into the Sago disaster.