Three children were rushed to a hospital after a "stink bomb" was reportedly released inside their classroom.
Multiple ambulances rushed to Fairfield Elementary School in Chicago, Illinois, on Thursday morning, after reports that students were affected by an aerosol irritant.
It is unknown who was responsible for the release of the harmful gas, which turned out to be a "stink bomb", a device designed to create an unpleasant smell.
"Stink bombs" are widely available products and range in effectiveness - from being used as simple pranks to military-grade malodorants or riot control chemical agents.
Paramedics transported three students to nearby Holy Cross Hospital, and said the trips were mainly precautionary.
Two of them were in good-to-fair condition and another in fair-to-serious condition, reported the Chicago Sun Times.
Thirteen more students and one adult were evaluated by paramedics at the scene but refused to be taken to the hospital.
The type of chemicals specifically released is unknown.
Back in 2018, a 16-year-old boy was arrested at Builth Wells High School in Powys, south Wales, UK, after he allegedly set off a stink bomb in the school.
About 500 children had to be evacuated from the school after the release of - what police described as - a discharge of a noxious substance.
Local reports described it as a stink bomb, and the school building had to remain closed for two days.
Staff reported that a ground-floor corridor appeared full of smoke.
Chief Superintendent Vicki Evans had said at the time: "We recognise that there may be concern among residents and visitors and wish to reassure everyone that the area was immediately contained to minimise any risk effectively.
"Communities may experience an increased policing presence, which should not cause any alarm – this is merely to reassure and support following this incident.
"The safety of those attending Builth High School and the wider public is our main priority, and as a result, we have made the difficult decision that the school will remain closed on Friday with a view to re-opening on Monday.
"The closure also currently affects Builth Wells Leisure Centre. We would wish to reassure you that we are aware that the closure of the school is a significant concern for parents, children and local communities and that we are making every effort to conclude this as soon as possible.
"Contingencies have been put in place by education partners to ensure minimal disruption to those children sitting examinations.
In a statement, the school had said: "We would like to reassure pupils sitting exams that if the school remains shut alternative arrangements are in place.
"Any concerns that have been raised will be taken up with the relevant authorities."
