§ 43.73. Bulkheads.
(a) Whenever the air pressure in a tunnel heading exceeds 21 pounds per square inch above atmospheric pressure, two air chambers shall be in use, except when headings are being started from shafts.
(b) Intermediate bulkheads may be required by the Department and the distances from the intermediate bulkheads to the heading shall not be greater than that prescribed by the Department.
(c) In all tunnels 16 feet in diameter or more, hanging walks shall be provided from working face to nearest lock. An overhead clearance of 6 feet shall be maintained and suitable ramps provided under all safety screens.
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