The long-awaited 24-page report was released by the agency on Monday and in it researchers said they found their answer to the crux of the research – whether there was a prevalence of a lack of sufficient start-up oxygen in the widely used SR-100s.

“NIOSH developed a protocol to test [and] determine if the failure rate of the start-up oxygen in the population of 70,000 field-deployed units exceeded 1 per cent,” the research group said, adding that it used American Society for Quality sampling procedures.

After pulling 500 units at random from across US coal mining operations, NIOSH assessed the group to determine if the units could be accepted as meeting the limiting quality rate of 1.25% for start-up oxygen performance – or no more than three failures from the entire lot.

“NIOSH observed five start-up oxygen failures in the 500 units it tested,” it said.

“The maximum number of failures allowed under the LQ rate of 1.25% was exceeded, therefore, the 1 per cent maximum allowable failure rate under the protocol was not met.”

The units selected were taken in phases and included various manufacture dates and places of origin.

An initial inspection for visual failures also removed a total of 10 rescuers from the first pool.

NIOSH found the units it observed that exhibited excessive start-up oxygen loss had been carried by a worker for at least some portion of their deployed lives and exhibited typical conditions of conforming fielded units.

It noted the unit with the largest total start-up oxygen loss was also the oldest of the group but it said the next largest total loss measured was in one of the two newest units.

In a May 2010 user notice, Pennsylvania-based CSE said it recommended redundancy in the event of an oxygen starter failure.

“If for any reason a unit does not inflate the breathing bag, the user should don another unit if one is readily available,” the company instructed.

“If a second unit is not readily available, the manual start should be used.”

Because “the availability of sufficient start-up oxygen is critical to the performance of the SR-100”, NIOSH director Dr John Howard penned a letter to MSHA Assistant Secretary of Labor Joe Main to share the researcher’s findings and called for its assistance for the next steps.

“Based on the findings of the investigation, the field‐deployed CSE SR‐100 units no longer conform to the minimum requirements for certification under 42 CFR part 84, subpart E,” he said.

“NIOSH looks forward to participating with MSHA in the planning and resolution of issues arising from the technical report … by providing appropriate user notices for mine users and other users and considering revocation jointly.”

An ILN request for comment from CSE was not immediately returned.