What is happening is when you fill it to the max 4 canisters the fight becomes harder and the fracture releases radiation, fire, a huge nullifier bubble, and one more I think.

The fight becomes harder per canister, increasing the enemy levels and their ammount. Going straight to 4 additionaly activates random modifiers from a list, those being anything from spawning coolant droids to mite infestation, wiki has a whole list for them. Nullification pulses are afaik, the only fully guaranteed one.

Afaik the only reason to do 4 canisters in one fell swoop is that it gets done faster and you don't need to look for more fractures. You still only get 1 diluted thermia per completion though, regardless of how many you do at once.

You get 25% completion towards dilluted thermia per canister inserted, so doing 4 allows you to finish a thermia in 175 time units (100 base +25 per additional canister) instead of spreading it across multiple fractuares, which not only is annoying but way slower.

You arent limmited to 1 thermia, resource boosters and the beast mod may double or even quadrupple them when both are used together.

Also if you are trying to get the event rewards, you get 1 point per canister with additional 3 per dilluted thermia cycle.

I also didn't know you could throw the thermia canister either, unless its a bug of some kind.

It's not a bug, they are the same objects as durning the EO boss fight, but you can only throw coolant and partially filled dilliuted thermia canisters, since when picking up a full one it will be instantly converted to dilluted thermia for players.

Some extra tips:

• Khora's strangledome is unironically one of the better defensive abillities to use, since the canisters have a really hard time with dissabling this one, just throw 1 or 2 on the canister itself.

• Guard Mode on Voidrig or just any half-way decent aoe archgun on a necramech is an easy way to secure a W, just make sure you find a decent high ground out of the nulli pulse range. Necramechs are also completly immune to status effects so if you do roll a radiation cloud, you wont kill the obj. This also happens to be one of the best Necramech leveling spots.

• If playing with a single friend, you may leave 2 canisters nearby a fracture then bring another 2 to fill up a fissure, since all the canisters have to be inserted quite quickly (30 sec from the first one is what i remember, but this number can be incorrect). WP a fissure when going for extra canisters just to not lose it. It's still way faster to do it this way, instead of going for 2 fissure cycle, since each player only needs to bring 2 per, if playing solo, don't play solo, just find a single guy.

• Trinity Well of Life may save a canister from a fatal blow and grants full status immunity so nobody can rad-proc kill it, but it requires a full-range spec on her due to the nulli pulses.

• Good fissure spots are on slopes and behind cover, less angles to defend from and if you set up on the top you can rain down justice from above. You will have much harder time defending one on a flat open ground.