Underground coal miners are facing a new and apparently growing safety threat: the theft of emergency air packs.

Authorities say the devices have been disappearing from mines, particularly in West Virginia, the nation's largest producer of underground coal.

Government regulations have forced the industry to store tens of thousands of extra air packs in unlocked, unguarded boxes underground so they will be readily accessible to escaping miners in an emergency.

The thefts come at a time when manufacturing backlogs have created a desperately short supply of air packs, or self-contained self-rescuers. Mine operators have taken delivery of 86,000 air packs and are awaiting 100,000 more to meet government mandates adopted after the Sago Mine explosion and other deadly disasters.

Authorities say it's tough to quantify the extent of the problem, but the thefts appear to be growing.

Richmond, Va.-based Massey Energy Co., the nation's fourth-largest producer by revenue, says it has lost at least 100 to 200 air packs. Other West Virginia coal companies say they have lost smaller quantities of the devices, which sell for more than $800 each, and Kentucky mines have reported scattered thefts as well.

"That's a lot, especially at the cost of each one of them," Massey spokesman Jeff Gillenwater said. "It's a noticeable problem."

One West Virginia mine operator reported 30 stolen air packs this month and Pittsburgh-based Consol Energy reports losing about 10 per month, said Randy Harris, engineering adviser for the state Office of Miners' Health, Safety and Training.

Authorities do not know who is stealing the air packs or why, but Harris suspects at least some are being sold to mine operators or contractors.

"Most likely the market is out of state for the big quantities," said Harris, who bought one for $25 at a yard sale six months ago that he used during performance testing. He recently found another at an antique store in Oak Hill.

West Virginia made it a felony last year to steal an air pack, yet the devices continue to disappear.

"Sooner or later somebody's going to show up at a cache in an emergency and it'll be empty," Harris said. "That's why we made it a felony in the first place."

Jim Kiser of Greenbrier Smokeless Coal, which lost 21 new air packs in a single theft, said the company has stepped up security, recorded serial numbers and is checking caches weekly.

"We constantly have a few things disappear," he said. "We've put every control we know to mankind in place to hold onto them."

Yet air packs still disappear occasionally, often in the hands of a former employee who takes a job at another mine, Kiser said. In response, Greenbrier is making sure everyone knows it's a felony to steal an air pack.

Massey is considering alarms and easily torn plastic ties on storage boxes, but Gillenwater, like others, hopes there will be fewer thefts becuase of a new Web site, www.minetheft.com, that lists the serial numbers of dozens of missing air packs.

"We think, quite honestly, that it's a good thing the industry is doing it themselves," Harris said. "That may be a very viable solution."

The leading air pack manufacturer, Monroeville, Pa.-based CSE Corp., is adding security detectors. CSE controls about 60 percent of the U.S. market.

"We have working models now, prototypes, and we'll be displaying that to the industry shortly, within a matter of months," company president Scott Shearer said.