Officials investigating the Sago Mine explosion are planning a test blast whose force will be nearly double the current federal standard for underground seals, apparently signaling their belief such forces could have occurred at Sago.

It also raises the possibility they believe the recently established federal standard may still be inadequate.

In the most recent test, set off Aug. 23, the planned blast "destroyed" two 40-inch Omega Block seals, according to a test protocol document obtained by the Pittsburgh Post-Gazette.

Two sources familiar with the test say the blast forces measured nearly 60 psi, exceeding the federal minimum 50 psi standard that seals must withstand.

But those sources also say the blast -- which led to the death of 12 miners -- left large pieces of debris, unlike Sago where the seals were pulverized into powder.

The new protocol calls for a 90 psi pressure pulse to be directed at both Omega Block and concrete seals. "This test is intended to help investigators evaluate the explosion and seal failure that occurred at the Sago Mine," the document states.

Setting the blast at 90 psi means "they must have some reason to believe the pressures reached 90 psi at Sago," said Joe Main, the retired safety director for the United Mine Workers of America.

U.S. Mine Safety and Health Administration spokeswoman Amy Louviere yesterday declined to comment on previous test results, citing the ongoing investigation. She did confirm that the sixth, and final, test "will be in the 80-100 psi range."

"We are evaluating the seals at different pressures in order to determine how they will fare and to see how extensive the damage will be at increasingly intense pressures."

The test blast protocol states that one of the destroyed seals was located in a crosscut, with the blast passing by from the side, while the other was directly in line of the blast.

Two other Omega seals in crosscuts remained intact.

Design specifications call for the seals to replicate the kind constructed at Sago, which differed in several respects from the design used when 40-inch Omega Block was first approved for use in mine seals. While NIOSH laboratories mortared the seals to the floor, and applied Bloc Bond mortar to all sides of the block as they stacked it, workers at Sago testified that they poured dry mortar onto the mine floor, stacked the blocks atop it, and at points squeezed mortar into joints after stacking.

Bennett Hatfield, president of ICG, the mine's owner, later insisted that designs did not call for the blocks to be cemented to the floor, but both MSHA and NIOSH engineers later said that the approved plan called for all joints to be mortared and that the point between the bottom of the wall and the mine floor would be considered a joint.

After building and curing new seals, scientists will conduct the blast Oct. 19 at Lake Lynn Laboratory experimental mine near Fairchance, Fayette County.

Investigators hope to learn more about why the seals at Sago were destroyed.

Regardless of subsequent results, "I think the evidence is already in on the Omega seal. People realize we should not be using those sealing methods in coal mines in this country," said Mr. Main.

The bigger question, he added, is whether the traditional concrete seals can withstand Sago-like forces. "If that thing fails, it's going to raise serious questions about seals in coal mines and whether they are adequate."

The tests are being done under the joint supervision of MSHA, the National Institute for Occupational Safety and Health, and the West Virginia Office of Miners' Health, Safety and Training.

In May, a McMurray-based structural engineer hired by ICG said the explosion at Sago was at least 60 psi and "could have been as high as 90 psi."

The engineer, Stephen Gerard Sawyer, reached that conclusion based on the damage to roof pans, roof bolt plates, brow support arms and belt hangers. Mr. Sawyer said he was unable to analyze the Omega Block seals because they "had been completely dispersed" except for a few blocks on the mine floor and some mortar remnants.

At the time of the Sago explosion, federal law required that underground mine seals be constructed to withstand a 20 psi force. In March, the Post-Gazette reported that a 20 psi seal would be considered substandard in industrialized countries.

When the Mine Improvement and New Emergency Response, or MINER, Act became law in June, it directed the Secretary of Labor to increase the minimum. In July, MSHA raised the standard to 50 psi, but some have questioned whether that is sufficient.

"I don't know what research was used to establish a 50 psi standard," said James M. Dean just before he stepped down as acting director of West Virginia's mine safety office last month.

"I'm thinking it needs to be higher."

Both MSHA and NIOSH engineers are exploring precisely that possibility, with each agency preparing for detailed computer simulations of various mine blast conditions. NIOSH has contacted the Sandia National Laboratory in Albuquerque, N.M., according to NIOSH engineer Mike Sapko.

NIOSH has developed a massive data set from previous explosion tests at its Lake Lynn underground laboratory, and that information would be fed into Sandia's supercomputer to construct various explosion scenarios to find out how to control methane buildups inside sealed mine areas, as well as what forces to expect when explosions occur.

At the same time, MSHA has already announced plans for a more focused computer simulation in an attempt to pin down the precise pressure exerted by the Sago blast.

Officials with that agency say they consider it important to determine the psi at Sago because, as the incident that spurred a temporary revision of the psi standard for blast-proof walls, it is likely to become the baseline for deciding how strong a seal wall should be.

One potential outcome of both simulations, though, is a look not only at the strength of walls, but the dynamics of gas buildups behind them. Mr. Sapko noted that some mines in Australia pump nitrogen or carbon dioxide into sealed areas to fill them with an inert gas to lessen the possibility of an ignition.