MASSENA — Massena Central High School Principal Alan C. Oliver has some advice about cellphones.

Don’t take them to bed with you.

His warning came after an incident at the high school on Jan. 23 that led to an “emergency dismissal” for students.

“As everyone knows, we had to do an early dismissal on Friday, the 23rd, due to a cellphone overheating and melting in a classroom. The resulting smoke made it impossible to carry on at school without some time to air out the building,” he said in a Facebook post.

The post included a photo of the melted cellphone and advice from Oliver.

“I am sending along this message as a parent. Both of my kids tend to fall asleep with their phones in their rooms/beds, especially on weekends. As you can see from the picture above (this is the actual phone from Friday), that could be catastrophic,” he said. “Please use this event at MCHS as an opportunity to have a conversation about the dangers of having a phone in your bed with you at night. This message is just as true for adults as it is for students.”

Charging a cellphone on a mattress or under a pillow restricts airflow, causing it to overheat and potentially start a fire.

Superintendent Ronald P. Burke said in this case the cellphone was in a student’s pocket.

“It in fact was a student who simply had the phone in their pocket which is a violation of our policy. It was not in use at the time,” he said.

This is the first year that students have not had access to their cellphones “from bell to bell.” In crafting their policy, district officials consulted with local stakeholders, including employee organizations representing bargaining units, parents and students to develop the policy that prohibits the possession of internet-enabled devices and personal technology by students during the school day on school grounds.

Burke said they do not know the cause of the phone’s meltdown. A melting cellphone is usually caused by a “thermal runaway” in its lithium-ion battery, where overheating leads to fire, smoke and structural failure, often caused by damaged batteries, improper charging or high temperatures.

Immediate risks include toxic fumes and fire, requiring rapid isolation of the device, ideally in a fireproof area, rather than using water.

“High school Principal Alan Oliver has shared with the high school community a cautionary tale that any such device has the potential to have a similar malfunction. His messaging was one of concern as we know many students and adults will often fall asleep with their device in close proximity,” Burke said.