RCW 49.24.130
Air chambers—Hanging walks.
(1) Whenever the air pressure in a tunnel heading exceeds twenty-one pounds per square inch above atmospheric pressure, two air chambers shall always be in use, except for such time as may be necessary when headings are being started from shafts; and whenever practicable the pressure in the outer chamber shall not exceed one-half the pressure in the heading;
(2) In all tunnels sixteen feet in diameter or over, hanging walks shall be provided from working face to nearest lock. An overhead clearance of six feet shall be maintained and suitable ramps provided under all safety screens.
[ 1941 c 194 § 6; Rem. Supp. 1941 § 7666-14.]
Structure Revised Code of Washington
Chapter 49.24 - Health and Safety—Underground Workers.
49.24.020 - Compressed air safety requirements.
49.24.030 - Medical and nursing attendants.
49.24.040 - Examination as to physical fitness.
49.24.080 - Requirements for underground labor.
49.24.100 - Lighting appliances.
49.24.130 - Air chambers—Hanging walks.
49.24.150 - Explosives and detonators.
49.24.160 - Air plant—Feed water.
49.24.170 - Electric power requirements.
49.24.190 - Cars, cages, buckets—Employees riding or walking.
49.24.200 - Speed of vehicles.
49.24.210 - Oil supply restricted.
49.24.220 - Explosives, use of—Blasting.
49.24.230 - Firing switch—Warning by blaster.
49.24.240 - Inspection after blast.
49.24.260 - Requirements as to caissons.
49.24.270 - Shields to be provided.
49.24.280 - Caissons to be braced.
49.24.290 - Cages—Hoisting apparatus.
49.24.300 - Buckets in vertical shafts.
49.24.310 - Telephone system for tunnels.
49.24.320 - Location of lights.
49.24.330 - Generators, transformers, etc., to be grounded.
49.24.340 - Electrical voltage.
49.24.350 - Lamps to be held in reserve.
49.24.360 - Insulators required.