Anonymous
when you open the vent if because you is thinking the drum is cool low temperature less 250F and pressure less 2 psig, (when you open the vent for an operator expert he can tell you if the drum still hot; for the sound or amount of the steam , etc) and then the operator procedure to drain the drum (there is some refinery after opening the vent they open the top flange) this take between 20 t0 30 minute