How a fire sprinkler works (155°F = 68°C)

They don't trigger in widespread areas, onky one at a time.
https://home.howstuffworks.com/home-improvement/household-safety/fire-sprinker-system.htm

There's no way to manually trigger it? That seems like less than a good idea

Personally I would think the pressure change of one triggered should cause a default activation of those nearby to control any spread. As for manually triggering, that has too much potential for abuse. Think how many people pull fire alarms for pranks. The damages caused by false sprinkler triggers would be crazy.

Well the sprinklers would be over_fire (;-) ) and if the fire spread the coverage would spread. The pressure drop doesn’t cause chain release, there are many sprinkler heads broken by accident during construction and renovation and chain release would be catastrophic.

But it would be safer to have the area already wet to prohibit or at least slow the spread in the first place.