The links in this quote don’t work any more, but this is one of the answers given:
This post gives some of the reasons for the minimum range:
Jurph also mentions a “cold launch” failure. In a cold launch, the missile is propelled out of the silo and then starts its engines, as opposed to a “hot launch” where the missile starts its engines inside the silo and the engines propel it out. In this case, the missile’s engines did not start and the missile went tail first back into the silo and exploded.
So the minimum distance in that case would be zero.
