When the PoCo went to disconnect service for non-payment, the meter ring came apart, leading to a service fault to ground.
The meter base was probably made just before WWII. Manufactured by Square D, the box cover had little slots, into which tabs on the ring were press-fit. Unfortunately, the meter socket was also attached to the ring- so when the ring came forward with the meter, the socket also cam forward, contacting the box.
At about 2 O'clock on the cover, you can see a round notch in the cover, caused by this arc.
Farther down the line, you can see the scorch mark on the EMT, caused by this fault arcing between the two pieces of EMT.
Best I can tell the meter-puller had to stand there, in the winter cold, confronted by hostile non-English speaking tenants, holding the meter in place- while waiting for assistance to come, and disconnect power at the pole!
Had a similar failure some years ago doing a service change working for EC here in So. Cal.
The cross piece holding the LINE side clips broke free while I was pulling the meter. The explosion shot the meter across the yard. Despite the fact that I was very stupidly not wearing proper PPE (just sunglasses and a t-shirt) all I got was a huge scare and ringing ears.
I climbed the ladder, cut the drop and removed that panel with a 20lb sledgehammer! The meter met the same fate. (Luckily for me, the POCO was going to upgrade the meter anyway. They laughed when I told them what happened.)
I'll be back with an edit of this post, to put up a link to a device designed to help safely pull and install meters. Don't touch that dial!
Anytime I come across a metercan that old (my utility has used ringless since the mid-60s), I climb a ladder and cut the drop before messing with it. If I'm not there to change the service, I don't mess with it. Ones I have opened are just too scary!