I just got back from the track today. I did wear my respirator at the beginning when the nitro buggy's were running heats.
It was a well organized race and there 24 heats.
Classes are nitro buggy , nitro truggy , E-buggy and SC. It was cool as there was about a 50/50 split between nitro and electric. So they would run 4 heats of nitro than 4 heats of electric.
This way it let the indoor place air out. There was a bit of wind and between the open doors and windows and fans the place was 'not' that bad as the wind picked up a little later in the day.