1. When you have done too much cocaine and you need to use a downer to even you out
2. Similar to a sniff safe, a fail safe against a bad comedown from cocaine, the blow brake is used to slow you down when you're too high.
Friend 1: What's the matter with you?
Friend 2: Dude my heart is racing, I think I might be od'in.
Friend 1: Just relax man, you're fine.
Friend 2: No man I'm grindin my teeth dull in there, people probably think I'm a scumbag coke head. Dude, engage the blow brake.
Friend 1: Alright man four beers comin right up!