Nearly one-third of emergency oxygen packs similar to those used at the Sago and Kentucky Darby mines failed inspection in federal tests performed before disaster struck at the two mines.

The problems with the CSE SR-100 model self-contained self-rescuers ranged from torn and stuck hoses, to dented and cracked casings, to damage from moisture, according to a newly released report by the National Institute for Occupational Safety and Health.

"I think what this points to is the importance of doing those daily inspections and doing them in the proper manner, adhering to the manufacturer's instructions," said Les Boord, director of NIOSH's National Personal Protective Technology Laboratory in South Park, which oversaw the tests.

The report, available on the NIOSH Web site, is based on evaluations of more than 400 SCSRs made by four different companies. The units were collected from mines throughout the country, then tested in two phases between 2000 and 2004.

It was in the second phase that NIOSH investigators found that 30 percent of the 98 SR-100 units they collected failed inspection. There was no information immediately available on the age or inspection record of the units.

"What we don't understand is, why is NIOSH testing damaged units?" asked Stacey Vernallis, legal counsel for the Monroeville-based CSE Corp., which makes the SR-100. If they're damaged, they should be taken out of service, she said.

The units, said Mr. Boord, were collected randomly from miners at the end of their shifts, without consideration of any obvious damage. NIOSH has been running such a program for years, sampling a few hundred self-rescuers each year and replacing damaged ones.

Ms. Vernallis questioned the reliability of such an approach.

"It would be interesting to see if the mine operators agree that these were randomly chosen," she said. If they know NIOSH is coming to replace damaged units, she said, "the operator is going to take 20 of their worst units so they can exchange them for 20 brand-new units."

Mr. Boord said the field evaluation results should not be extrapolated to the mining industry as a whole. And he noted that even those units that did not meet inspection standards still had the minimum one-hour of oxygen when tested.

Based on the most recent findings, however, Mr. Boord said NIOSH will likely expand its sampling program. "We do recognize the importance and the need to redesign the program so we can attain more statistically significant data from the samples."

The NIOSH report seems certain to draw renewed attention to the self-rescuers, which all miners have been required to carry underground since 1981.

After 12 miners died at Sago in January, survivor Randal McCloy Jr. reported the doomed crew could not get four of the units to work.

Paul Ledford, who survived a methane explosion at the Kentucky Darby Mine in May, later told family members that his SR-100 lasted only five minutes.

Since then, the federal Mine Safety and Health Administration has increased miners' self-rescuer training from one to four times a year and there has been added emphasis on inspecting the units.

But questions about the self-rescuers -- and their maintenance, in particular -- have persisted.

In July, the Pittsburgh Post-Gazette reported that one of the tested self-rescuers at Sago was past its 10-year service expiration date, and six others were within two years of expiration.

Under the grueling conditions of underground mine work, self-rescuers get battered and scraped daily, and may be exposed to extreme heat and moisture.

Scott Shearer, president of CSE, said the company in recent years has added indicators to show if the unit's integrity has been compromised from wear and tear, high temperatures or moisture. It also has a reusable training unit in production that will simulate breathing through a real self-rescuer.

"Our No. 1 focus is to make sure miners have a unit that's going to work when they need it," said Mr. Shearer. "But we're kind of like Ford. We can sell you the car, but we can't make you change the brakes."

The NIOSH field evaluation found problems with other models, too.

Self-rescuers made by Ocenco had inspection failure rates of 19 and 23 percent in the two phases, while the Draeger and MSA models were 5-8 percent. The MSA Life-Saver 60, which had a 5-6 percent failure rate, is no longer in production.

Nearly all of the testing was done on a simulator. According to the report, humans testing the units started coughing because of corn starch particles. The particles were meant to prevent saliva from entering the unit's chemical bed where it would speed up the reaction with potassium superoxide, unnecessarily using up oxygen. The corn starch is no longer used.

Each model met the one-hour oxygen supply standard, and the Ocenco EBA 6.5 tested at more than 100 minutes.

The market-leading SR-600 had the highest inspection failure rates, 19 percent in the first phase and 30 percent in the second. It had other problems as well:

More than 10 percent of the units had "little or no starter oxygen," requiring the wearer to manually start it.

In the second phase test, 18 of 98 units had hoses stuck to each other, some of which tore when extended out.

Hoses on about 10 percent of the units had punctures or slits.

Five of the 98 were described as difficult to open.

Dirk Fillpot, spokesman for the U.S. Mine Safety and Health Administration, said yesterday that agency experts "are reviewing the NIOSH studies and it is premature to comment at this time on NIOSH's results."

What they do know, said Mr. Boord, is that their work is not done.

"Clearly the test did find degradation of material, and they found various factors that made the device less than optimal, which then goes back to looking at ways to improve SCSRs."