Reminds me of an incident at work about 20 years ago!
Alarm bell rings on station, both Fire Aplliances despatched to fire.
After a minute or so a message comes over the radio 'Can you stop immediately theres a mechanic on the roof.'
You should have seen his face, I've never seen anyone so white
He had arrived on station to carry out a minor repair and had failed to inform anyone. I dont think he ever made that mistake again.