Hazardous materials teams responded to a reported explosion at a chemical lab Monday afternoon in Andover, Massachusetts.
Firefighters described a strange green cloud outside the Morpho Detection building when they first arrived on scene at about 5:30 p.m.
"I thought it was someone going over a speed bump," said Andrew Kennedy, an office worker who heard the blast from across the street. "It was a large a boom, shook the building a little bit."
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According to the Massachusetts Fire Marshal's Office, there was an explosion when two acids appeared to have come into contact with each other at the Frontage Street building.
"An employee placed a chemical inside a waste container which should not have been a problem," said Andover Fire Chief Michael Mansfield. "There’s some belief that there was another chemical inside that waste container."
The company specializes in equipment that detects drugs and explosives in airports.
Nobody was hurt in the explosion but the roughly 100 workers inside had to be evacuated.
"Engineers that are familiar with the materials that they’re working with," explained Mansfield. "And they were very surprised they had some sort of reaction."
NBC Boston reached out to the company for a comment but so far there has not been a response.