An investigation into a chemical plant explosion that shook a Massachusetts neighborhood and sent four people to the hospital has found no evidence to suggest that it was caused intentionally.
State Fire Marshal Stephen Coan said Wednesday that investigators plan to bring in independent experts and try to determine what testing might be needed to figure out the cause for Sunday's blast and fire at the Bostik Inc. complex in Middleton, about 20 miles north of Boston.
The plant makes adhesives and sealants.
Bostik Inc. is headquartered in Wauwatosa, Wis., and is part of Bostik S. A. based in France.
Bostik Inc. President and CEO Bill Campbell said "there are no known environmental concerns" and people working in its administration and research buildings have returned to work.