One explosion happened on the second floor of 'S' building while the other happened in the school's commons area, prompting the evacuation of the campus.
Wednesday morning around 9 a.m., Spokane firefighters responded to the school for the first pop bottle explosion. According to a firefighter, the 2-liter bottle that exploded was filled with dye.
Spokane Public Schools spokesperson Terren Roloff said there was not hazardous material in the bottle and there was no threat to students or staff.
Then, around 11 a.m., there was a second explosion at the school. Soon thereafter school officials confirmed they were evacuating the campus.
"All Ferris High School students are being released early today as a precaution, so that fire department officials can continue their investigation of the materials that caused the two plastic bottle explosions today. Students who ride the bus will be taken home on their regular routes," Kristy Mylroie from Spokane Schools said in a media release.
A janitor suffered some skin irritation cleaning up chemicals from one of the pop bottle devices.
The police department commented about the incident via Twitter, calling the situation "more of a malicious mischief nuisance than any threat to students," and identified in broad strokes, the devices that exploded as a "distraction device."
Adams Elementary, located across 37th Avenue from Ferris High School, was not evacuated.
The school is working with both the Spokane Police Department and Spokane Fire Department to determine what materials were used in both explosions, as well as search the campus to see if there were any other pop bottle devices.
Several students are being questioned by authorities but no arrests have been made.
Spokane Schools said that this is finals week and classes will resume Thursday. Fire officials said that these types of incidents are common across the country during finals week.