Two of the DTS engine dyno shops I use to use in SO CA had positive dyno room pressure with the intake and exhaust fans running with the engine being tested running at idle or anything less than WOT shock
Once I figure out that meant the motor being tested had from 1 to 4 lbs. of boost being added at WOT I had them leave the dyno room doors open after that up
I have seen them turn the inlet fans off after a pull and open the dyno room doors with the exhaust fans left on and then forget to turn the inlet fans back on before starting the next pull, they could tell the difference in sounds at WOT at the beginning of the pulls which would make them stop the pull to turn on those fans and restart the pull over work shruggy
As W.J. the professor said many times , we don't race dyno, do we whistling

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)