I have a story too, related to this.
I used to work in a medium sized supermarket in the UK around 2007. We had no backup generators. Even the back office computer had no backup power - no UPS. The cash registers were small windows machines, and any EFT payments were done via the computer in the back office. The store was big enough that people could easily hide in the store in the event of a blackout.
The residential areas in the village often lost electrical power in winter but usually the store would be OK as it was on a different part of the grid along with the doctors surgery and some other businesses. We weren't that lucky that day.
I worked evening shifts, and once the power did go out during my shift. Store policy was to get all customers to leave and secure the store, locking yourselves inside until you can contact the alarm company to verify that the alarm is indeed still working and can be armed. We were then supposed to cover the chillers to keep the heat out and wait out the outage with the emergency lights (or go home if it got too close to closing time, meaning the store would not be reopened that day).
The building was badly maintained. While it looked clean and modern on the shop floor (ground floor) it was actually a very old building, and the upstairs floor (staff only, where we keep the big walk in fridge/freezers and stock) looked like it hadn't been refurbished since the 1950s. It was a very dangerous floor - sharp metal shelving sticking out, discarded refrigeration units, all sorts of things. And that's just the part of the upstairs we usually visit. There is also a back section to the upstairs floor that NO ONE likes to visit - rumour is it is haunted (I don't believe that but it has very dark walls and a high roof so it looks scary at night). The back section of that floor housed the control gear for the 30 year old walk in fridge/freezer - big control panels with neon lamps, and a no longer used (for over 30 years) butchery room with a dumb waiter. I wish I had taken photos of this stuff.
I was serving on the cash register. The lights flickered, and about a minute later - poof, everything went dark. The emergency lights did not come on so no one could see anything. My supervisor remembered that I always carried around a light - a Fenix P1D CE at the time - and shouted out for it. We herded the customers out of the store and locked the main door. I needed to go upstairs to get a second light (only 1 light for 3 people? not enough!) and everyone followed me as they were too scared to be left alone in the dark store.
As soon as we started to go upstairs, there were some very weird noises from up there - clanging sounds. My other colleagues screamed, so I bumped my light up to max output and scanned the area. It calmed them down, but the inky black walls swallowed the lumens like a cave. We ran to the staff break room and I retrieved another light from my bag upstairs and lent one to the supervisor. By the way, the upstairs floor had no emergency lights fitted at all. The noises? It was coming from the ancient walk in freezer. It doesn't like power being cut to it suddenly.
We checked the office and could not find a single flashlight for use by the employees. If it were not for my lights, we could have been in a dangerous situation with customers hiding in the store and stealing stuff (sadly, the area was dangerous). Sure we had some 2xAA incan lights in stock to sell and we could have opened up a couple in an emergency but you would need to find them in the pitch black store - plus they would have not been that helpful especially on the upstairs floor.
Power came back on, but it was too close to closing time so instead we decided to just make sure everything was OK for the night. My supervisor asked me to check upstairs. The lights were working now which was a relief, but the freezer didn't come back on. We were supposed to call our maintenance department but my supervisor had enough and wanted to go home, so asked me to go and check the control panels incase it was something simple.
I had to go to the section of the upstairs floor no one wants to go near. I approached the hall way to that section, and.... the light switch didn't work. Out comes the P1D. I notice that this section of the floor has old fashioned incan fittings rather than tube fluorescents (weird), and that the incan bulb directly above me is smashed and the rest are missing! That did send a bit of a chill up my spine, but armed with my P1D I went to the control room. This room did have a working light but it was a really dim incan. I examined the control panel and toggled the start switch for the freezer. Thankfully it did start up.
A few weeks later someone came and replaced all of the emergency lights.
After this incident, I was known as the guy with the lights, and I was always tasked with checking the upstairs portion of the store at lockup time. Part of the reason for that is the light switch for the upstairs area is in the most stupid place ever - it's in the middle of the upstairs floor. So you have to look blindly for it if you don't have a light.... a health and safety disaster to be honest.
This brings to mind the fact that the store registers may not be opened, and they may not be able to give cash change. It may be wiser to carry five $20 bills instead of a single $100. Just a thought.
