NORTH ANDOVER (CBS) — Five people were injured in an explosion at the Dow Chemical facility in North Andover.

Three of the injured were taken by medflight to Boston hospitals, one was taken to Lawrence Memorial Hospital and another was treated at the scene.

Dr. George Kondylls, an emergency room physician at Lawrence Memorial Hospital says the victims are suffering from burns related to the blast involving the chemical trimethylaluminum.

Emergency crews responded to the plant on Willow street around 2:30 p.m. Thursday.

The explosion occurred in a lab and caused damage to the building. State Fire Marshal Stephen Coan says the explosion occurred when the chemical reacted with water or air.

“What we know is that the chemical we speak of here is highly reactive to water and to air,” Coan said. “So that’s why the investigation is leading itself in that direction.”

Trimethylaluminum is a key ingredient in making LED lights.

Coan says as of Thursday night, investigators had not been able to gain access to the lab where the explosion happened.

Four lab workers were seriously injured, but were able to walk to the ambulance before they were transported.

There is no threat to surrounding residents and businesses, town manager Andrew Maylor told WBZ-TV. Chemicals were not released into the air, Maylor said.

A spokesperson for Dow said “Our thoughts and prayers are with the families, friends and colleagues during this extremely difficult time. An investigation is underway to determine the cause of the incident.”

A worker was killed in an explosion at the same facility in 2013. Coan said that incident involved a different chemical and is not related to Thursday’s explosion.