You'd have a 20A circuit protected by a 20A breaker. There would be no more risk of a fire than if you had a 40A circuit protected by a 40A breaker. If there's a fire it would be the fault of the 20A breaker for allowing >20A...
Really wouldn't be that much different to how regular 110v outlets are wired. You're allowed to put 10 outlets on a 20A circuit even though each outlet could pull 12A.... 'cause 99.9% of the time you're not going to have more than one thing plugged into that circuit pulling 12A. If you try to run a vacuum and a space heater the breaker trips... no fire... just a tripped breaker. You reset the breaker and move on with life