30 CFR § 57.4660
Work in shafts, raises, or winzes and other activities involving hazard areas.
During performance of an activity underground described in Table C-2 or when falling sparks or hot metal from work performed in a shaft, raise, or winze could pose a fire hazard--
+---------------------+-----------------+-------------------------+
| Activity | Distance | Fire hazard |
+---------------------+-----------------+-------------------------+
| Welding or | | More than 1 gallon of |
| cutting with | | combustible liquid, |
| an electric arc | | unless in a closed, |
| or open flame | | metal container. |
| Using an open flame | Within 35 feet | More than 50 pounds of |
| to bend or heat | of-- | non-fire-retardant |
| materials | | wood. |
| Thawing pipes | | More than 10 pounds of |
| electrically, | | combustible plastics. |
| except with | | |
| heat tape | | |
+---------------------+-----------------+ |
| Soldering or | Within 10 feet | Materials in a shaft, |
| thawing with | of-- | raise, or winze that |
| an open | | could be ignited by |
| flame | | hot metal or sparks. |
+---------------------+-----------------+-------------------------+
(5) Cover or bulkhead the opening immediately below and
adjacent to the activity with noncombustible material to prevent sparks or
hot metal from falling down the shaft, raise, or winze. This alternative
applies only to activities involving a shaft, raise, or winze.