English to Russian Tech/Engineering Petroleum Eng/Sci

Since it can be very difficult to decoke a Coke Drum that has been in coking service for less than 4-6 hours, stopping the feed to a Coke Drum before that point is not recommended for a normal shutdown.
Dealing with a Coke Drum that has unconverted residuum in it can be very dangerous.
It is important to note that the shutdown of a Coke Drum prior to the Coke Drum being in service for 4 hours will produce a tarry drum.