4.12.714 TANK CAR OPERATIONS
(1) Caution signs shall be so placed on the track or car as to give necessary warning to persons approaching car from open end or ends of siding. These signs shall be left up until after car is unloaded and disconnected from discharge connections. Durable signs shall be at least 12 by 15 inches in size and bear the words "Stop-Tank Car Connected" or "Stop-Men at work". The word "Stop" shall be in letters at least 4 inches high and the other words in letters at least 2 inches high on a background of contrasting color.
(2) The track of a tank car siding shall be substantially level.
(3) Brakes shall be set and wheels blocked on all cars being unloaded.
(4) Tank cars of anhydrous ammonia shall be unloaded only at permanent storage locations.