I opened the door to enter the office building lobby. The sound was loud and unmistakable - an electrical transformer humming away, loudly. Following the sound I found the room about 20 feet away with the door propped open to help ventilate the transformer.
The photo shows a simple steel louver in the door for ventilation, too. Obviously it was not enough to keep the temperature of the electrical room within perceived acceptable limits. The door may have been propped thinking lower temperature would help reduce the humming. For power transformers, the hum is mechanical in nature caused by the core laminations when magnetized. Time and increased temperature can weaken the laminations causing the hum to increase. Additional cooling will not reverse lamination damage, nor reduce the hum.
The humming and temperature were not the only difficulty with this room. The hollow metal door and frame are both fire rated. The rating is unknown because the labels were painted over. And the louver in the door was not a fire rated louver. So the fire rating of the exit access corridor is compromised by this electrical room door, even without being propped open.
The International Building Code (IBC) references NFPA 80 (2007) - Standard for Fire Rated Doors and Other Opening Protectives as the standard for fire rated doors. In the 2007 edition of NFPA 80, annual fire door inspection was added to the standard.
This door is the poster child for why annual inspections are necessary.