In the before time (late 90s) I worked for a company that worked for a company that worked for a company that provided software engineering services for NRC regulatory compliance. Fallout radius simulation, security access and checks, operational reporting, that sort of thing. Given that, I spent a lot of time around/at/in nuclear reactors.

One day, we're working on this system that uses RFID (before it was cool) and various physical sensors to do a few things, one of which is to determine if people exist at the intersection of hazardous particles, gasses, etc.

This also happens to be a system which, at that moment, is reporting hazardous conditions and people at the top of the outer containment shell. We know this is probably a red herring or faulty sensor because no one is present in the system vs the access logs and cameras, but we have to check anyways. A few building engineers climb the ladders up there and find that nothing is really visibly wrong and we have an all clear. They did not however know how to check the sensor.

Enter me, the only person from our firm on site that day. So in the next few minutes I am also in a monkey suit (bc protocol), climbing a 150 foot ladder that leads to another 150 foot ladder, all 110lbs of me + a 30lb diag "laptop" slung over my shoulder by a strap. At the top, I walk about a quarter of the way out, open the casing on the sensor module and find that someone had hooked up the line feed, but not the activity connection wire so it was sending a false signal. I open the diag laptop, plug it into the unit, write a simple firmware extension to intermediate the condition, flash, reload. I verify the error has cleared and an appropriate message was sent to the diagnostic system over the radio, run through an error test cycle, radio again, close it up. Once I returned to the ground, sweating my ass off, I also send a not at all passive aggressive email letting the boss know that the next shift will need to push the update to the other 600 air-gapped, unidirectional sensors around the facility.