In a multi-page letter from West Virginia Office of Miners’ Health, Safety and Training director CA Phillips issued Friday, shelter manufacturers have until October 31 to inspect all underground mine shelters after a discovery that some brass valves and fittings failed.

Cracks that were found in some can render the units inoperable.

An incident with the fittings at an unidentified mine in the state was first discovered earlier this year and resulted in an investigation by both state and federal officials.

The WVOMHST said the unit was constructed by AL Lee and that an initial determination revealed a “catastrophic failure” where the pressure build-up from inside the unit forced both the deployment and air-lock doors open, ejecting contents from inside onto a mine rib.

“The demonstrated unpredictable service life of the [components] is troublesome,” Phillips said in the letter. “The current situation, left unchecked, represents a safety hazard.”

Phillips added that any further delay in an inspection push could result in more failures.

The WVOMHST has also mandated that all West Virginia operators replace all of the brass valves and fittings on all units’ compressed oxygen cylinders by December 31, 2013.

The agency will enforce the order by requiring that all of the state’s mines add an addendum to its emergency shelter plan with a refit certification and submit that documentation to officials.

“We have to make sure [shelters] are going to operate the way they are designed to operate," Phillips said.

Mine shelters, also known as refuge chambers, began to be used widely across the US industry following a string of incidents in 2006 where workers died because they could not be reached for rescue before being overtaken by the dangerously gassy and smoky environment.

The shelters, along with air supply caches, then became mandated under the Mine Improvement and New Emergency Response Act of 2006, or the MINER Act.