(CNN) -- Police cars and fire trucks surrounded Jefferson County Open School in Colorado Monday, as hazmat crews decontaminated students outside -- spraying them down, fully clothed, in cordoned-off sections under a blue tent.
Students coming in after recess had reported eye and skin irritations. Thirty kids and a teacher's aide were eventually treated for symptoms similar to an allergic reaction, according to CNN affiliate KUSA. A handful were taken to the hospital. The rest were evacuated to a church down the street.
The K-12 Colorado school remained closed on Tuesday as investigators tried to figure out what "toxic irritant" had been released on the playground.
They quickly figured out that it wasn't fertilizer or pepper spray, KUSA reports.
Six habanero chili peppers caused this hot mess.
Investigators found the spicy fruits scattered in the wood chips near the playground, school district communications director Lyyn Setzler told CNN. It isn't known how the peppers got there, she said.
Habaneros generally score between 100,000 and 350,000 units on the Scoville scale, which measures chili pepper hotness.
"The scale is actually a measure of the concentration of the chemical compound capsaicin, which is the active component that produces the heat sensation for humans," according to ChiliWorld.com. For comparison, jalepeno peppers usually score 2,500 to 5,000 units.
When you grind (or step on) habanero peppers, capsaicin particles can be released into the air. Breathing them in or getting them in your eyes can cause a burning sensation.
"As a person who grows some painful peppers, I have learned the hard way to take heed when handling them," says CNN Eatocracy editor Kat Kinsman. "It's all fun and games until you get some pepper juice in your eye, and then it's as if the sun is exploding."
The school is washing down the playground equipment and surfaces that may have been exposed to the pepper oil, KUSA reports. The wood chips are also being replaced.
All the students who were brought to hospital for evaluation were released the same day, and all are fine, according to the local fire department.
Setzler says the school expects to re-open tomorrow morning.
CNN's Stefan Simons contributed to this story.