The agencies said they observed the manufacturer’s evaluation of the SCSRs on April 23, using the M-20s that had reportedly malfunctioned.

“The reported units were refilled and tested by the manufacturer and did not malfunction when the units were donned,” officials said.

MSHA and NIOSH urge operators to follow Ocenco’s complete instructions for donning M-20 SCSRs when performing annual tests that are specified in mines’ emergency response plans.

In the meantime, federal officials continue to contact mine operators to determine if any problems have been identified when the annual tests are performed.

“Any problems encountered should be reported to MSHA,” the agencies said.

The two initially issued an alert notice about a report of faulty units late last week after an unidentified mine reported a malfunction involving four of its M-20s.

Those units had been produced in 2008.

An ILN request for comment from Wisconsin-based Ocenco was not returned.

The SCSR maker’s two primary products are the M-20.2, a belt-worn unit designed for 20 minutes of breathable air and the EBA 6.5, often stored in caches, which allows for more than 90 minutes of oxygen.

A guide to the care and maintenance of Ocenco M-20 units is available at www.msha.gov/InteractiveTraining/SCSR/Ocenco%20M-20/lesson06/Instructors_Guide_OCM20.pdf .