30 CFR § 75.207
Pillar recovery.
Pillar recovery shall be conducted in the following manner, unless otherwise
specified in the roof control plan:
(a) Full and partial pillar recovery shall not be conducted on the
same pillar line, except where physical conditions such as unstable floor or
roof, falls of roof, oil and gas well barriers or surface subsidence require
that pillars be left in place.
(b) Before mining is started in a pillar split or lift--
(1) At least two rows of breaker posts or equivalent
support shall be installed--
(b)(1)(i) As close to the initial intended breakline as
practicable; and
(b)(1)(ii) Across each opening leading into an area where full
or partial pillar extraction has been completed.
(2) A row of roadside-radius (turn) posts or equivalent
support shall be installed leading into the split or lift.
(c) Before mining is started on a final stump--
(1) At least 2 rows of posts or equivalent support shall
be installed on not more than 4-foot centers on each side of the roadway;
and
(2) Only one open roadway, which shall not exceed 16 feet
wide, shall lead from solid pillars to the final stump of a pillar. Where
posts are used as the sole means of roof support, the width of the roadway
shall not exceed 14 feet.
(d) During open-end pillar extraction, at least 2 rows of breaker
posts or equivalent support shall be installed on not more than 4-foot
centers. These supports shall be installed between the lift to be started and
the area where pillars have been extracted. These supports shall be
maintained to within 7 feet of the face and the width of the roadway shall
not exceed 16 feet. Where posts are used as the sole means of roof support,
the width of the roadway shall not exceed 14 feet.