The Pennsylvanian manufacturer notified the US Mine Safety and Health Administration this week that it had progressed its investigation of specific serial numbers outlined in the earlier announcement, but that the source of the issues with those units had still not been found.

“Until the root cause can be identified, we must assume that the potential for start-up oxygen cylinders to fail may extend to any field deployed unit, and not just the serial numbers that were previously identified,” the company said.

“Pending final resolution, CSE is notifying all customers of procedures to be followed if there is any question about unit activation.”

While it did not detail the recall of more units, CSE did urge miners in any emergency situation to don a second SCSR unit, if one is available, if for any reason the first one does not inflate the breathing bag. If a second unit is not readily available, individuals should manually start the unit.

“The SR-100 primarily uses a chemical process to generate the oxygen needed for the 60-minute supply provided by the unit,” CSE explained, pointing out that there are two activation methods.

“The oxygen cylinder is designed to inflate the breathing bag when the user pulls the large fluorescent orange oxygen actuator tab while donning the SR-100.

“In the event the compressed oxygen starter does not activate or the oxygen vents through the mouthpiece because the plug is left out of the mouthpiece during activation, the user has an alternative start procedure available.”

If another unit is not available, it added, the SCSR can be started quickly without the cylinder’s oxygen. Instructions for manual donning are included in the SR-100 user manual, as well as in the training materials for the rescuers which are part of federally required quarterly training.

“As CSE continues to investigate, we will be contacting any customer that may have purchased a unit required for our continued research. In the meantime, any questions may be directed to our customer service representatives at 412-856-9200,” the company said.

CSE’s February statement said that some of the units targeted might be receiving less-than-optimum oxygen during start-up.

“Through its quality control program, [we] identified an oxygen cylinder received from its supplier that presented an issue that CSE is investigating as to the potential that the breathing bag in an affected SR-100 unit may receive less than the optimum amount of oxygen necessary for full inflation, if the unit is started with the oxygen cylinder,” the company elaborated this week, saying that its investigation was continuing.

The initial recall was believed to have involved only a small portion of one lot of 4000 SR-100s that were produced in May 2009.

CSE told various media Tuesday that, while the concern had now expanded to two lots and as many as 11,000 units, it had opted to take the extra precaution of informing everyone.