The state's mine safety office warned coal mine operators Tuesday that heat damage to emergency air packs could be more widespread than originally thought.

Recent tests and an inventory of emergency air packs prompted the Office of Miners' Health Safety and Training to warn underground mine operators and contractors to make sure air packs aren't exposed to heat sources, such as hydraulic lines and heavy equipment.

The notice sent out also directed mine operators to remove any air packs suspected of exposure to high temperatures and to notify the agency.

The testing and inventory were conducted in reaction to the Sago Mine disaster that killed 12 miners in January, and another mine accident later that month in which two men died in a conveyor belt fire.

The state sent a similar notice in August after preliminary tests of air packs carried by its mine inspectors found evidence of heat damage. That notice focused on air packs made by Monroeville, Pa.-based CSE Corp., which has about 65 percent of the national market. CSE manufactured the emergency air packs used by the Sago miners.

On about a fourth of the 10,500 air packs in use across the state, potential damage from heat exposure couldn't be determined because they don't have sensors, said mine safety chief Ron Wooten.

The biggest concern involves the CSE air packs. The inventory shows about 2,500 CSE air packs lack temperature sensors, while temperatures sensors had been tripped on 63 newer units.

The inventory also found about 70 air packs made by Pittsburgh-based Draeger Safety that lack temperature sensors and 15 made by Pleasant Prairie, Wis.-based Ocenco Inc. with heat damage.

CSE President Scott Shearer said the notice and an accompanying report highlighted his own concerns. He mining industry must undergo a culture change to prevent poor care and handling of air packs.

"It takes the industry to address this," he said.

CSE has been under scrutiny since the Jan. 2 explosion at the Sago Mine. Survivor Randal McCloy Jr., who has sued CSE, has said four members of his 12-man team could not get their CSE air packs to work. Federal testing shows the devices were able to generate oxygen.