You are right. MDF dust is horrible (Some are even carcinogenic I believe) so we cant just limit it to MDF. But when in the arena it should not matter. If people are worried, covering the RR arenas top net with say a clear plastic sheet to trap the dust might be a solution to stop it reaching the crowd. Thought with no spinners allowed I cant see there being much dust...

Side: Can you run spinning twack bots like Stinger or Bladerunner (US middle weight) in the RR arena? When at full speed Bladerunner's spike tipped tail was doing around 50mph.