It is widely considered that the act of removing covers from electrical equipment could in itself increase the risk of an arc flash.

Removing the last screw with your knee jammed into the cover while trying to keep it in place can be interesting - especially when the cover slips. Also a less than desired experience is when the cover is removed and something unexpected that was left by the last person mysteriously drops and you hear that heart stopping "ping" as it hits something in the panel.

So here is this week's question.

Have you (people you know) ever had an arc flash from opening or removing covers on equipment?

Yes
No
I/We don't perform electrical work

Stories are encouraged!

Yes! When I was an electrician in the field in 1996, I was working on an 800amp 480v electrical panel in a plant. I was working with another Journeyman and we were taking the cover off of the panel. When we were taking the screws off the right hand side of the panel, an arc flash occured. The only thing we could figure was the screw had been tightened into the insulation but not faulted and we disturbed it causing the fault. The side of the panel blew out and the main tripped. We did not have arc flash PPE on but the cover of the panel shielded us from the shrapnel.
Interestingly enough, 6 months later this same journeyman was working on this panel again and tightened one of the "wing" clips into a 500mcm conductor causing another arc flash!

I was involved in an arc flash incident - while collecting data for an arc flash report. The front cover of a small transformer was being removed when it was discovered the entire top of the transformer needed to be removed in order to remove the front. This was a 480V-208/120V transformer. The process involved a running process that could not be "shut down". The transformer was a 3R type. In the bottom a mouse had made a nest and when the cover was moved the mouse jumped toward the person startling them which caused the front cover to short the on the leads. No one was injured and the process did get shut down when the fuses blew.

The take away - arc flash generally happens when you are doing something and you never know when the arc flash will happen.

Been doing this for 35 +years, and have never had this happen,
or known it to happen to anyone I have worked with.

There have been a couple of "near misses" though, including one
where there was NO WAY we were putting the cover back on, without a shutdown.

What was the purpose of removing the transformer housing (for an arc flash study)?

Same answer as the others. Opening a panelboad. The outer cover slipped and fell into the bus work. Minor fault though so no injuries.

I noticed throughout all of the above commentary though a similar thread. My thoughts about "failure modes" on covers in general is that covers held on by bolts only can and do fall into live equipment for a variety of reasons. There are four exceptions to consider when it comes to whether arc flash PPE should be needed for covers:
1. Exposed live bus or cables behind the panel. Newer equipment more and more is "touch safe", so even if a panel fell into the interior for whatever reason, an arc flash is not likely.
2. Cables installed WAY too long on the idea that if they have to be reterminated over and over again eventually the ends will be so short they won't reach. NEC 8" rule should apply here, and should not increase in length just because the cable size/voltage is higher. Failure to follow this results in overstuffed troughs in MCC's (hazardous in itself for overheating) and potential pinches cables. So this goes back to "properly installed and maintained".
3. Various bits of metal stuck into the door and not secured to cover holes, especially after modifications. What can I say, "proper installation"...one arc flash case in the OSHA accident investigation summary database details about the only case I could find of "normal operation" of a breaker initiating an arc flash because a piece of metal fell into the panel.
4. Round covers, like manholes, can't fall into anything.
5. Hinged doors, at least if they are "properly maintained" (not bent/broken), again can't fall into anything.
6. Again from OSHA accident investigation logs, parts/tools on top of a panel or sitting on a ledge in a panel that roll off and into the bus. I've had more than one time where this happened but fortunately it didn't set off an arcing fault. In some plants this could also take the form of electrically conductive dusts or mud. One of my standard practices is that before I open a door, I first sweep the top of thedoor and the panel (and sides) off of any debris that could fall into the panel. More than once this has saved me from further problems.

I've sent electricians to the ER when they were (against instructions) working on live panels and dropped something that created an arc. Looking back on some of the things I did when I was an electrician, I'm amazed I'm still in one piece.

Yes - In 2008 I was working with a third party developer of a large wind farm to turn it over to the utility that I worked for. As part of the OEM commissioning and turn over process for the hundreds of turbines, a crew would travel ahead of us and take off the metal panel covers in the base of the towers. These would be left off so we could go from turbine to turbine to verify phase and voltage. Then a follow up crew would reinstall the covers. While installing a cover this crew left a tower door open. The wind caught a panel cover and blew it into the 600 V terminations causing an arc flash. One technician was severely burned and had smoke inhalation, the other jumped or was blown out the door and had minor scratches. The turbine was a total loss after the fire. The OEM later added a hinged non conducting cover to protect from contact with terminations along with changes to the verification process.