The current regulations for seals, known as MSHA 30 CFR 75.335, were drawn up in two subsections that were both part of a ventilation directive update in 1992. The first, (a)(1), includes the use of solid concrete blocks, or “Mitchell-Barrett” blocks, and (a)(2) outlines alternative methods and materials based on a pass-fail test of 20psi minimum.
A series of public information bulletins, or PIBs, were issued on the subject during June and July following the incident, Sherer said at the MSHA/NIOSH/UMWA ventilation summit held recently at the MSHA Academy in Beaver, West Virginia. All were rescinded except for PIB P06-16, outlining 50psi alternative seals, on July 19.
In P06-16, new alternative seals must be capable of reliably withstanding overpressure of up to 50psi. Additionally, the seals must be designed with their end use in mind – the design must match the conditions, they must be certified for use by a structural professional engineer (PE), and senior mine management at the operation installing them must certify the materials used for construction.
In terms of existing seals, MSHA’s responsibility will be to inspect all that are already constructed and in use for construction accuracy. In terms of the alternative seals, the agency inspectors will evaluate the atmosphere behind them as well as look at the seals’ integrity.
The PIB also outlined items for 20psi alternative seals under explosive atmosphere (3-20% CH4 and +10% O2) and high-risk seals. To remediate these units, Sherer outlined inerting the atmosphere, reinforcing the seals to 50psi, constructing an additional alternative seal able to withstand 50psi for that area, and the construction of additional Mitchell-Barrett seals.
For those considered “high risk”, however, including a hazard that would affect miner safety, the agency has put forth that additional actions be taken, such as the periodic monitoring of the atmosphere behind the seal structure.
Ventilation issues were also taken into account in the PIB, with vent plan information required for each mine. The requirements include a map of the area to be sealed, the details of the seals to be used, the size of the opening, any data relating to geotechnics and geology, associated construction drawings and specifications, all quality control procedures and the PE’s certification of the design and application of the seals.
Also illustrated in the directive is the requirement for a detailed seal design, which encompasses an engineer’s analysis or information on the material and its durability.
Moving forward, Sherer said the agency is working hard on the seals section of the MINER Act, all of which is set to be put into place in the industry before year’s end. It is currently revising that seal standard and a proposed rule on the topic is expected in May.
