So my wife and I woke up today to find a strong acidic smell coming from our home office. The door had been closed all night so the smell of vinegar hit us strongly when we entered the room. It wasn’t the normal smell you get from a failed electrical component. I’m well used to dead capacitor smell! The smell was more like vinegar, or a car battery acid smell.
Obviously this sort of strong acetic odour in a confined space is a worry, and with a bit of electrical equipment in the room there is a risk of fire when something goes wrong.
The odd smell was unusual though. In 25+ years in IT I hadn’t smelt anything quite like it in a server room or office, and my nose was not helping me as I started sniffing everything in the room.
To cut a long story short… it was the APC battery backup, or UPS (Uninterruptible Power Supply). It was the first thing I suspected, but before I starting shutting down everything did a quick search on google for “UPS vinegar smell’ and “UPS acid smell” and most articles referred to the rotten egg smell of Hydrogen Sulfide. This smell certainly wasn’t like that, and it wasn’t until I came across this thread ( https://community.spiceworks.com/topic/450206-strange-odor-in-server-room?page=1 ) that I found other people with a similar issue.
Swollen batteries are very hard to remove from UPS
If you smell a strong smell in your office or server room, if it smells like acid, vinegar, used car batteries, sulphur, or rotten eggs… turn off your UPS immediately and unplug it. Move it to somewhere you can safely open it. It’s probably going to be hot, very hot, so grab a towel.
Our UPS was almost too hot to touch. I shut it down, unplugged the power and then unplugged the battery module. After moving the UPS to a work surface I attempted to remove the battery bay and found the batteries had swollen so much it was almost impossible to remove the battery tray. Two of the batteries in particular were extremely hot and their casing buckled.
I’m very glad that we picked up the smell so quickly, and that this didn’t happen while we were away. It is a good reminder that UPS batteries need to be replaced on a regular basis, and you should power off any electrical items you aren’t using for an extended period.
For me, I can add a new smell to my IT troubleshooting toolkit. The smell of acid, the vinegar stench of failed batteries.
Two faulty batteries off-gassing acetic fumes
So if you smell a strong acid odour (or acid odor if you’re American), don’t delay, check your UPS!
Oh, and although I didnt think to do this immediately, VENT THE ROOM. An off-gassing battery may be producing “strong inorganic acid mists containing sulfuric acid” which is a category 1 carcinogen (inhalation). MSDS PDF
An APC battery tray with two swollen and very hot batteries.
