The U.S. Mine Safety and Health Administration this morning posted an updated notice about the problems with the most widely used model of self-contained self-rescuers in the nation’s coal-mining industry.

You’ll recall that back in February CSE Corp. announced a recall of about 4,000 of its SR-100 model SCSR units. See our print story about that here and a Coal Tattoo blog post here.

At the time, CSE President Scott Shearer said the problems — related to the oxygen cylinder that jump starts the units — were limited to just one lot of SR-100 units made in May 2009.

But in its new “Notice to Users,” CSE says this:

CSE has progressed in its investigation. 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. CSE is continuing to investigate. Pending final resolution, CSE is notifying all customers of procedures to be followed if there is any question about unit activation.

CSE Corp. President Scott Shearer, with one of his company’s widely used SR-100 SCSRs.

UPDATED:  In an interview this afternoon, Shearer told me that the company now believes that at least two lots of SR-100s — up to 11,000 units — could be affected. And, the company is actually not “recalling” any of the units. Instead, CSE is advising mining companies to simply re-enforce training of miners in how to manually start SR-100s that don’t seem to be working properly.

As we reported previously, the problem now being examined by CSE was similar to problems reported by Sago Mine Disaster survivor Randal McCloy and by other miners who have complained about SCSRs not working properly:

The SR-100 model made and marketed by CSE uses a chemical process to generate the oxygen needed for a 60-minute supply of breathable air.

Generally, SR-100 units are started by pulling a large orange tab that activates an oxygen cylinder. The cylinder inflates a breathing bag. Once a miner starts breathing through the bag, the exhaled gases react with the unit’s chemicals to generate more oxygen for the miner.

… SR-100s can also be started manually if the oxygen cylinder fails to inflate the breathing bag. But that process involves breathing ambient air and exhaling into the mouthpiece to start the chemical reaction.

In its February warning notice, CSE said it had identified “a possible issue with a component part” involving a shipment of oxygen cylinders:

CSE is investigating the potential that the breathing bag in the affected SR-100 units may receive less than the optimum amount of oxygen necessary for full inflation, if the unit is started with the oxygen cylinder.

In its new warning, CSE offered this advice to miners and mine operators:

If for any reason a unit does not inflate the breathing bag, the user should don another unit if one is readily available. If a second unit is not readily available, the manual start should be used.

The SR-100 primarily uses a chemical process to generate the oxygen needed for the 60 minute supply provided by the unit. There are two methods for activating the SR-100. 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 readily at hand, the unit is designed to be quickly started without oxygen from the cylinder. Instructions for the manual start are detailed in the SR-100 User Manual. Instructions are also in the training materials; they are part of the required quarterly training for users.

MSHA and NIOSH have said that they are investigating the problems … but so far, the government agencies haven’t said much of anything about what they’re investigating or what they’ve found.

An estimated 70,000 SR-100s are in the field, in coal mines across the country …