When it happens, you won't hear it.
The Département du Déminage in France is still very busy. Six hundred engineers have died in the line of duty, and farmers are killed every year.
With the annual ploughing up of old war junk goes the epithet "the iron harvest": Special army patrols still drive around the countryside picking up old grenades which the farmers put in piles beside the road. Even 80 years after the war, every year there are still accidental deaths caused by live ammunition exploding. Farm workers are at greatest risks, because their machines do not discriminate between buried grenades and sugar beets, potatoes or other root-crops, and, of course, because they work on the former battlefield each day. For example, in 1991 a total of 36 farm workers had died when their machines hit duds (today 39).Old grenades, which penetrated deeply when they hit the ground without exploding, slowly make their way towards the surface, like those oft cursed stones in Irish and Swedish fields, which when the frost thaws, reach the surface making life miserable for the poor farmer. This happens not only to stones and duds, but to things like stone age axes and other archaeological artifacts. The stone, thus, rises a little bit each year, due to the frost heave. The same thing happens accordingly with duds, small or large.
The Swedish historian Dr Peter Englund writes in the magazine Vi, no 17/18 (1997), pp. 20-36., that (translated from Swedish) "in Belgium 126 have people died and over 400 been wounded in explosions during the last 50 years" (p. 27.).
Oh, it happens. There's a good deal of unexploded ordnance still lying around places like France, left over from a century's worth of wars. Every so often you'll hear about some poor French farmer who accidentally finds one by hitting it with a plow or some such, and manages to blow himself straight to the moon.
During World War Two, Fort Macon in North Carolina was reactivated and the U.S. Army actively manned the fort with Coast Artillery troops.
The Ripley's "Believe It or Not" cartoon headline was:
CONFEDERATE SHELL WOUNDS YANKEE SOLDIERS.......... 80 YEARS AFTER IT WAS FIRED
I have a Civil War Bormann shell, Parrott shell and a Hotchkiss shell myself as historical relics but they have all been deactivated.
By odd coincidence, I recently sat thru a talk that examined UXO (unexploded ordnance) and how frequently it kills people who handle them. In the US, more than 50 people have been killed by exploding fuzes, bombs, mortars etc. So they do kill folks. I don't know what portion of them were civil war era. I do know that the explosives experts approach ordnance from that era with even more caution than they do modern pieces because of the nature and instability of the explosive.
The really amazing thing about this talk was how many folks find UXO out in a field, pick it up and bring it home to put on the mantle or for the kids to play with. That's how most of the deaths have occurred.
Black powder is very unstable compared to smokeless powder
I own a good sized collection from 1763 Charleville flintlock to 1846-1898 Colts (plus S&W, Allens, Remingtons, Sharps, etc.) and can tell you a still loaded Civil War percussion revolver is still very dangerous - much more so than a smokeless cartridge loaded weapon
All firearms are loaded and all deadly - until carefully proven otherwise
Learning safety with explosives, shells, cartridges, weapons comes before firing and accuracy.
Skipping safety may mean firing and accuracy is never learned.
OK - I'm finished on safety -
Now I need to go kill something outside....
110 years old is not civil war era. 1895 would be Spanish American War era. Things then were actually not that much different, on a fundamental level, than now. We were still using black powder in our Krags, but the Spanish had smokeless for their Mausers. They also had machine guns, while we mostly had old Gatlings, and not many of those. It's a good thing our Navy wasn't as backwards as our Army.
Actually, about 25 years ago in Virginia (I think Goochland County), a kid brought a "Civil War" - ..ahem .. "War Between the States" - artillary shell to school. He had the bright idea of making an ashtray or something out of it in shop class. As he was tightening a vice on it, it exploded killing a couple of kids. The tragedy received a lot of media coverage in Virginia and left quite an impression on me. The town was shell-shocked. So to answer your question, that was the last time I heard of such a shell exploding. The principal did exactly the right thing in evacuating the school and calling in the bomb squad.