The federal agency responsible for mine safety announced yesterday that it has more than doubled the minimum standard for mine seal construction.

Beginning immediately, walls built to block off portions of an underground mine must be able to withstand a force of 50 pounds per square inch, or psi. The previous standard was 20 psi.

The U.S. Mine Safety and Health Administration announcement said mine operators and MSHA officials will check the thousands of existing seals built under the 20 psi standard "to determine whether additional measures are necessary to protect miners."

In March, the Pittsburgh Post-Gazette first reported that the 20 psi standard in U.S. mines was far below those in other industrialized nations, including Australia, Canada and South Africa.

David G. Dye, acting administrator for MSHA, cited the explosions this year at the Sago mine in West Virginia and the Darby mine in Kentucky as reasons for the change.

In both instances, Omega block seals failed to withstand methane gas explosions, leading to the deaths of 17 miners.

Based on investigations of the two tragedies, the higher standard is needed "to better protect miners from explosions behind sealed areas of underground coal mines," Mr. Dye said.

The MSHA announcement also noted that preliminary data "suggest that there are problems with the construction of some alternative seals in use in underground coal mines."

Under the new regulation, designs for alternative seals will have to be certified by a professional engineer and the construction certified by a senior management official.

Luke Popovich, spokesman for the National Mining Association representing coal mine operators, said the group has no objection to the higher standard.

"I'm sure it's fully justified," he said.

But Dennis O'Dell, administrator for occupational health and safety for the United Mine Workers of America, said he doesn't think the new standard goes far enough.

"I don't know what science they used to come up with that," he said. "I think they've jumped too soon," noting that seals testing by federal officials since Sago have not been completed.

Australia sets a minimum standard of 50 psi, but Mr. O'Dell said that comes with restrictions such as a required evacuation of a mine as the methane gas buildup behind a seal moves through the 5 percent to 15 percent explosive range. Once methane exceeds 15 percent, there is insufficient oxygen for an explosion to occur.

Said Mr. O'Dell: "I hope that maybe this is just a baby step, and they will increase it" beyond 50 psi.