“That appears to have been either a water main or a sprinkler main that broke prior to the collapse”
A sprinkler main break should have caused the fire alarm to sound.
It will cause an alarm if it is past the riser. There is a 8” main or so coming in from the street that is unmonitored except by the water meter. Once inside the building it may be above or below the ground.
A waterflow alarm should not be silenceable until the flow has stopped by code.