At least four people were seriously injured in a chemical explosion at Dow Chemical Company's North Andover, Massachusetts, plant on Thursday afternoon, according to authorities
First responders were stll at the scene on Willow Street hours after the explosion was first reported.
State Fire Marshal Stephen Coan said that the investigation will begin once the scene is cleared by hazmat crews, and that it appears a chemical reacting to water - trimethylaluminum - caused the explosion.
Lawrence General Hospital spokesperson said earlier that four patients suffered critical injuries due to shrapnel and burns from the blast. Three of those patients are now stabilized and were transferred to other Boston area hospitals.
A fifth person was not seriously injured and refused treatment.
North Andover Town Manager Andrew Maylor said it doesn't look like there's an ongoing problem at the site.
A Dow spokesperson said that the families of the injured workers have been notified, and that there are no imminent risks to the surrounding community at this time.
A Peabody man was killed at the same chemical plant in a 2013 explosion; however, Coan said there doesn't appear to be a connection between Thursday's explosion and the 2013 incident, which involved a different chemical.
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Federal and state authorities have been alerted. Two inspectors from OSHA were dispatched to the scene, as well as some area haz-mat teams.