They took a man into custody for questioning at Cornerstone Academy in San Jose after he gave them a hard time while they tried to fight the fire.
He was later arrested for outstanding warrants and held on a mental health hold.
"There was a person of interest on scene that was hampering our firefighting operations. That person was detained by San Jose Police and arson investigators. (He was) yelling at the fire engine crews, they had hose lines dropped on the ground and he was getting in the way, just erratic behavior that didn't make any sense," said Captain Brian Palodichuk of the San Jose Fire Department.
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The fire at the school on Lucretia Avenue was set just outside the school's central office. The principal got the call at 6a.m.. By school time, she had decided not to cancel classes.
"The kids are safe. The classes are going on. The WiFi is up. So it wasn't really what we anticipated our Friday morning to be. There have been a lot of challenges this year. This is another one we have to deal with," said Principal Marion Dickel.
Firefighters had already been to the area on Lucretia Avenue for a few small fires before the big fire at the school's office at 6a.m.
"There were just small piles of rubbish that were found across the street from the school. From 3a.m. to 6a.m. there were three to four small fires. The final one was the big one," Captain Palodichuk said.
Investigators don't think the school was targeted.
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"We have no reason to believe that right now. The investigation is ongoing. I spoke to the principal there, she doesn't believe the school is being targeted. It's unknown why this fire was started in this area," he said.
The school fire followed two other large fires. Investigators do not think they are related.
The first of the three happened at 10:53p.m. Thursday night on Eastside Drive and N. White Road. It started in some storage units in a communal area of some residences.
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"It ended up burning four different residences. There are homes in six different detached structures. They were like in-law quarters. That was a big fire, it was three alarms, it tied up a lot of our resources," he said.
The second one happened Friday morning on Park Johnson Place and Honolulu Drive.
"The second fire came in at 2:00 in the morning. That was a residential fire, which had a heavy fire load in the side and back yards. It was tough for our crews to get in there and get access. That tied up a lot of our resources. And then the fire that came in at 6:00 in the morning (at the school). I'd like to add the same crews were at the fires. It was a long night. They are tired. We are proud of the work they have done," the Captain said.
No injuries were reported.