Coal mine inspectors across Pennsylvania and the United States will begin checking this week to see if coal miners can successfully don and operate the emergency oxygen packs they carry underground every day.

Before the disaster at West Virginia's Sago mine, this was a yearly assessment. Now it will happen every three months.

"We're going to try to get to as many as we can in the next two weeks," said Joseph Tortorea, acting district manager for coal mine safety and health in Western Pennsylvania.

"As with any device, if you don't use it every day, or you don't have any experience, it may appear difficult to use."

The self-contained self-rescuers, or SCSRs, have become a focal point for the families of the dead Sago miners after the sole Sago survivor, Randal McCloy Jr., told them in a letter that four of the 12 packs failed when the men tried to use them.

Testimony at last week's hearing in Buckhannon, W.Va., also revealed that even successfully deployed self-rescuers had more oxygen in them -- from 28 percent to 79 percent unused -- when recovered by rescue team members.

"None of them was used up 100 percent, and that's unacceptable," said Russell Bennett, son of miner Marty Bennett, one of the 12 miners who died at Sago after a Jan. 2 methane explosion trapped them.

"I agree with you," replied John Urosek, a ventilation expert for the federal Mine Safety and Health Administration. "That's a question on all our minds, why they were not used fully."

Family members say the self-rescuers malfunctioned and have requested model numbers, serial numbers and manufacturing dates for the Sago devices.

Investigators are not so sure they malfunctioned.

"The tests that we've completed so far indicate that they did start when the miners tried to do that," said Richard Gates of MSHA, the accident investigation team leader. "Exactly what happened, we don't know at this point."

The emergency oxygen packs recovered from Sago are undergoing additional testing at a federal laboratory in South Park.

Les Boord, director of the National Personal Protective Technology Laboratory, said he was "not aware of serious problems" with self-rescuers before the Sago disaster but is currently reviewing that data.

"Like any other respirator, you need to know how to put the unit on and start the unit," he said.

The CSE SR-100 rescuers used at Sago require a multistep process: After looping the pack's strap over his head, the miner lifts a latch to remove both top and bottom covers, pulls an oxygen activator tag, puts the mouthpiece in his mouth and puts on a nose clip and goggles.

The oxygen is activated when the miner breathes into the mouthpiece.

The fact that the self-rescuers at Sago either malfunctioned, were not properly used or were not fully used raises several questions, said Joseph A. Sbaffoni, director of Pennsylvania's Bureau of Mine Safety.

"Did the miners put them on right away? Or did they breathe in carbon monoxide and get disoriented? Maybe they weren't thinking straight," he said. "Carbon monoxide will sneak up on you quick. Maybe they just passed out and stopped breathing."

Even veteran miners might not have a lot of experience using the self-rescuers they carry every day. Mr. Tortorea said the devices are used in emergencies only once or twice a year in Western Pennsylvania's 43 underground mines.

One danger is "over-breathing" -- trying to breathe in oxygen faster than the self-rescuer can produce it. "It will continue to work," said Mr. Sbaffoni, "but it's going to feel like you're not getting enough. It's going to feel like you're sucking through a straw."

Both miners' families and mining officials agreed on one point -- it is time to look at making the oxygen packs better.

"Why have we not improved these things? They're basically the same as they were 20 years ago," said Jack Spadaro, former director of the National Mine Health and Safety Academy in Beckley, W.Va.

At Sago, the 12 trapped miners made at least one attempt to escape before barricading themselves in and waiting for rescue. When the men could not get the four oxygen packs to operate, some shared the remaining ones.

Because it took rescue teams 41 hours to reach the men, it's unlikely that the self-rescuers would have saved more miners. Even when a miner remains sedentary, the devices don't usually last more than four to six hours, officials say.

On the other hand, grieving relatives point out that Mr. McCloy survived -- and many wonder if a few extra hours of oxygen might have brought them a survival miracle, too.