A small explosion in a Nevada high school caused a lock-down and a partial evacuation this week. The cause? According to USA Today, Washoe County School District police are blaming an e-cigarette.

Around 10:15 am Monday morning, a faculty member reported a fire in the gym. School officials subsequently called the police. Principal Kevin Carroll then evacuated the roughly 150 students who were in the gymnasium and surrounding classrooms.

District spokeswoman Victoria Campbell said that the initial cause of the explosion was not released right away and that the investigation of the incident was ongoing. She says that the students were “messing with” an e-cigarette but had no intentions of causing the explosion.

The incident may be a result of the students operating the e-cigarette incorrectly.

E-cigarettes are usually constructed of three different parts: a cartridge to hold the nicotine-infused liquid solution, a heating device, and a battery.

Although many people feel that e-cigs are safer for smokers’ health than traditional cigarettes, experts say that incorrect use of e-cigarettes could be dangerous — especially in regard to the battery and charging. Since not all chargers are compatible with all e-cigarettes, there is a risk of malfunction if the wrong charger is used. This may have been the case in the Nevada incident.

“First and foremost, e-cigarettes are not intended to be used by minors,” said Matt Taylor, manager at Studio Vapor. “The community provides numerous vape shop locations to inform others about the safety uses and the hazards of devices and accessories if used improperly. We encourage any e-cig user to seek out and utilize the information your local vape shop has to offer so problems like this could be avoided.”

E-cigarettes are gaining popularity in the United States, since they are an alternative to traditional tobacco cigarettes. There about about 2.5 million e-cigarette users in the U.S.