I've found an incredibly simple method to successfully prevent most tantrum spirals.
If you run the rest of the fort properly, this method can easily make your industries run smoothly while getting dozens of dwarves killed.
The big evil source of all tantrum:
Meeting halls.
Having no meeting halls prevents tantrum spirals:
-If you have a meeting hall, dwarves will meet.
-When dwarves meet, they become friends.
-When half your population commits to !!science!! or other fun, the remaining half which were friends of them go out of control.
So, it is as simple as this:
-No meeting halls: No meeting.
-No meeting: Limited amount of relationships
-Weak relationships: Low amount of sadness when Urist McScience undergoes an unforeseen lethal event.
-Low amount of sadness: No tantrums
The downside is that you will have idle dwarves wandering outside and in tunnels, solvable by burrows or by physically locking them in with forbidden doors and the like. However: the further they spread out the better!
Combining this with something that makes the dwarves happy, like masterfully engraved personal bedrooms will allow them to take the emotional hit of losing a handful of Urist McSockgrabbers during an ambush without shedding a tear.
Last but not least, have a coffin ready for every dwarf. This limits the emotional impact of deaths substantially.
You will never have enough coffins. If you run out when needing them, it is over.
Build a few hundred. You are gonna need them.
So:
No meeting -> no friends -> no sadness -> no tantrum.
A lonely dwarf is a happy dwarf.
In my fortresses it is the other way around. Meeting halls (combined with dining halls and a personal 3x3 room for everyone) are the things that prevent Tantrum spirals from happening. At all. I'm playing DF for a few years now and I NEVER EVER had a tantrum spiral. That said, three essential things I have in every fort are:
Meeting hall, often decorated with statues. When I train my smelters I usually process raw ore in masses, if there are valuables amongst them (like gold or silver) the meeting hall gets floored with it.
Dining hall, often with tables and seating for 90+ dwarfes. Simply entering the room causes a huge happiness rise because of all the furniture (90+ tables and seats, surplus statues and maybe gold floor plating)
Personal 3x3 room for everyone, simple, with a bed, coffer and cabin. Also reduces the amount of XXstuffXX lying around a lot.
And thats it. These three things make dwarfes so happy that they ignore half the fortess and all of their family dying.
That said, meeting halls can be huge tantrum spiral preventers if correctly utilised
I'm with you. Can't remember the last time I had a tantrum spiral -- maybe 20 or 30 forts ago. I always make a dining hall, smoothed and engraved, with high-quality tables, chairs, and statues. I give each dwarf a nice 3x3 bedroom, usually smoothed but not engraved, with a quality bed, door, and cabinet. Always build 2 or 3 statue gardens and a high-quality well for them to hang out at. Always build paved roads with good (like marble) to high-quality (like gold or platinum) material. I don't like the idea of keeping them isolated.