You are correct, there is no mention in the rule book. Why would you think about it? Maybe because a pressurized charge is a bomb? And that bomb is how far away from your vital parts? It's not always the rules that dictates what you should do.
The turbo guys should think about that 150,000 rpm grenade under them.
FIM motorcycle specification:
Superchargers and turbochargers shall be separated from the rider, either by a
cover of steel plate at least 3 mm thick or a ballistic blanket that meets SEMA
specifications 14-1, or by a vehicle or engine structure that provides equivalent
protection.