On Saturday, “an individual committed arson on a newly purchased ICE building” by breaking a window, igniting a fire and throwing a propane tank into the building, according to a U.S. Department of Homeland Security spokesperson.
“The fire was quickly extinguished by the interior sprinkler system,” DHS said, noting that the suspect fled the scene after setting the fire. “The matter remains under investigation by the FBI.”


You can easily release the sprinkler pressure from the outside before setting the building on fire.
Just out of curiosity, how?
Break a couple of sprinklers that are accessible outside. The system is pressurized. They last about 30 minutes depending on how many valves are open.
Commercial fire systems treat a sprinkler activation as an alarm condition. You wouldn’t be able to wait around for 30 afterwards. Fire department would be there which would cause issues for your plan.
Modern commercial fire systems are very good. There are no simple solutions for arsonists. They would need physical access to the building disable the fire systems, or to be able to produce enough fire to overwhelm the spriniler’s abilities to extingush it.
Few have both the will and ability.