The thing that concerns me the most is how different people react to caffeine. With some, caffeine has little effect on them physiologically, but for some, blood pressure goes way up, heart rate is increased, etc, etc. We advise not to drink coffee after a hard workout session, so how is drinking it after a job any better???
Maybe it'll raise the already elevated blood pressure of a bunch of firefighters that just got done working hard to a dangerous level. But I don't really think a cup or two of joe is really gonna be the straw that broke the camels back so to speak, though it could.