DYFED-Powys Police and partners are dealing with an incident at Builth Wells High School, Builth Wells.
Shortly after 11am today (June 13) police received a call reporting the discovery of a substance causing breathing difficulty and nausea to those exposed to it.
A multi-agency response was activated and is ongoing. The primary focus of this response is to ensure the safety and welfare of all pupils and staff at the school, and members of the public in the surrounding area.
Specially trained officers from all agencies attended the scene and conducted an assessment which has indicated the substance is not believed to be a danger.
Around 20 people were exposed to the substance; they were triaged by Ambulance at the scene and deemed well enough to go home.
We would like to reassure the community there is no wider concern for health or safety in connection to this isolated incident.
A 17 year old boy has been arrested, he remains in police custody and the investigation is ongoing. Police are treating this as an isolated incident which is not believed to be terrorist related at this time.
Health advice has been issued to all affected by this incident, and there is not a concern for the wider public. If anyone affected feels unwell but the problem is not a medical emergency, please call NHS Direct Wales on 0845 46 47 for advice and guidance.
For updates on school closures, visit www.powys.gov.uk which will contain the most up to date information for the school. Parents are encouraged to check this throughout the evening in relation to tomor