Under the MSHA plan, miners who rove around underground -- such as safety examiners or water pumping crewmen who don't have easy access to backup caches of units -- must be given a different model SCSR or a backup SR-100 to wear within 30 days. All other miners must be given new or backup equipment by April 26, 2013, and all SR-100s must be out of the mines by Dec. 31, 2013.

MSHA chief Joe Main has defended the nearly two-year timeline for replacing all of the units.

"Due to the large number of CSE SR-100s in underground coal mines, multiple SCSRs available to miners, the low probability of failure and the shortage of immediately available replacements, MSHA and NIOSH have determined that an orderly phase-out will better protect the safety of the miners than immediate withdrawal of the devices," Main said.

The United Mine Workers union has also defended the MSHA plan.

But Main has also said that SCSR manufacturers are able to produce about 6,000 new units a month, meaning the 66,000 SR-100s in the field now could be replaced in a little less than a year.

MSHA officials have said it's not that simple.

"For an orderly transition to take place, a number of steps are involved," said MSHA spokeswoman Amy Louviere. "It takes time to ramp up production, orders, distribution, etc. The various types of SCSRs have different characteristics, and mine operators can choose a particular unit or combination of units to meet the needs of their operation and the regulators."

"While we estimate that 6,000 total units can be produced per month, not all units can be interchanged in caches, on belts, etc.," Louviere said. "In addition, mine operators may want to stay consistent with the model they have chosen for their mine, and not co-mingle different SCSRs, to make training easier and lessen potential confusion for miners."

Last month's long-awaited NIOSH report confirmed a "critical" defect in the oxygen bottles meant to kick-start CSE's SR-100, the mining industry's most widely used model of SCSR.

The U.S. Mine Safety and Health Administration bought 300 new self-contained, self-rescuers, or SCSRs, last year and has ordered another 600 replacements for SR-100 models made by Pittsburgh-based CSE Corp.

In West Virginia, the state Office of Miners' Health, Safety and Training is making an emergency order to replace any SR-100s currently assigned to its mine inspectors.

Late last month, MSHA and the National Institute for Occupational Safety and Health announced a plan to phase-out the coal industry's use of the SR-100, after a NIOSH report confirmed long-standing complaints from miners about problems getting the units to work.

The phase-out announced by MSHA gives mine operators until Dec. 31, 2013, to replace any and all SR-100 units they have with other models of SCSR approved by the agency.

MSHA spokeswoman Amy Louviere said last September's purchase of replacements for more than 300 SCSRs used by agency inspectors was timed as part of the routine replacement process as those units reached the end of their estimated life.

Another 600 were ordered just after last month's announcement of the industry-wide phase-out of the SR-100, Louviere said.

"The ones that are being phased out now are part of the regular replacement cycle for those that are nearing their expiration dates," she said.

State officials are in the process of buying replacement devices for about 40 SR-100s used by West Virginia mine inspectors, said agency spokeswoman Leslie Fitzwater.

CSE stopped making and selling the SR-100 and last year began marketing a new model of SCSR that the company says is smaller, lighter and produces 40 percent more oxygen than the SR-100, which was rated to supply at least one hour of breathable air. Other SCSR makers include Wisconsin-based Ocenco and the German firm Drager.

Under the MSHA plan, miners who rove around underground -- such as safety examiners or water pumping crewmen who don't have easy access to backup caches of units -- must be given a different model SCSR or a backup SR-100 to wear within 30 days. All other miners must be given new or backup equipment by April 26, 2013, and all SR-100s must be out of the mines by Dec. 31, 2013.

MSHA chief Joe Main has defended the nearly two-year timeline for replacing all of the units.

"Due to the large number of CSE SR-100s in underground coal mines, multiple SCSRs available to miners, the low probability of failure and the shortage of immediately available replacements, MSHA and NIOSH have determined that an orderly phase-out will better protect the safety of the miners than immediate withdrawal of the devices," Main said.

The United Mine Workers union has also defended the MSHA plan.

But Main has also said that SCSR manufacturers are able to produce about 6,000 new units a month, meaning the 66,000 SR-100s in the field now could be replaced in a little less than a year.

MSHA officials have said it's not that simple.

"For an orderly transition to take place, a number of steps are involved," said MSHA spokeswoman Amy Louviere. "It takes time to ramp up production, orders, distribution, etc. The various types of SCSRs have different characteristics, and mine operators can choose a particular unit or combination of units to meet the needs of their operation and the regulators."

"While we estimate that 6,000 total units can be produced per month, not all units can be interchanged in caches, on belts, etc.," Louviere said. "In addition, mine operators may want to stay consistent with the model they have chosen for their mine, and not co-mingle different SCSRs, to make training easier and lessen potential confusion for miners."

Last month's long-awaited NIOSH report confirmed a "critical" defect in the oxygen bottles meant to kick-start CSE's SR-100, the mining industry's most widely used model of SCSR.