Firefighters were called to the city lot at 714 Charles Street just before 5 a.m. and quickly extinguished the flames.
Three Seattle Police Department patrol cars and a van were damaged in the fire.
City workers spotted a suspicious man just before the fire broke out, said Officer Jeff Kappel with Seattle police. As the workers tried to contact the man, an explosion occurred near the police vehicles and the man took off running.
SeattlePI.com reports a law enforcement source told them there were fliers left behind at the scene that specifically mentioned the case where a King County Sheriff's deputy was accused of beating a 15-year-old girl inside a SeaTac holding cell. The deputy has since been fired, and Seattle police had no involvement in that case.
Thursday's fire sent shockwaves through the neighborhood. A witness in the area said he heard explosions before firefighters arrived.
"(The sound) was more than a gunshot -- I thought it might have been a grenade," said David, who lived nearby. "And then another big boom and that's when I got on 911."
He said he ran outside in his boxers to see what was going on.
"I saw just flames 30 to 40 feet everywhere. I thought it was going to blow the whole yard up," he said.
No one was hurt, but police worried there could be more explosives planted in the yard. So they brought in special remote controlled robot to sniff around for trouble.
Meanwhile, police converged on the area and were searching beneath nearby freeway overpasses for anyone who may have been involved. Police only have a vague description that he was roughly 6 feet tall, wearing dark clothing and was carrying a backpack.
In 2007, someone set fire to a dozen city vehicles at the same facility, including several police cruisers.