CITY (AP) - Police officers spent two hours investigating a suspicious plastic container found behind a Missouri sandwich shop before determining it was a high school science experiment.

KMBC-TV reports that police were summoned Tuesday to a Jimmy John’s in Platte City on the northern edge of the Kansas City metropolitan area.

The plastic container they encountered was filled with blue fluid attached to other items. Officers eventually determined it was an experiment meant to demonstrate how hydrogen can be used as power.

The student who built the project demonstrated it to friends inside the Jimmy John’s then left it behind the store so other friends could see it. But a worker at a nearby convenience store spotted the gadget and called 911.

No charges are expected.