The facility was licensed by the town to store 12,000 gallons of flammable chemicals, but had about 24,000 gallons on site, according to the state fire marshal's code compliance investigation.
The explosion in the facility, shared by ink manufacturer CAI Inc. and paint and adhesive maker Arnel Company Inc., destroyed 19 surrounding buildings, including some homes, and damaged 250 other buildings as well as cars and boats. Twenty people were hurt, but there were no deaths.
Prior investigations have blamed the early morning explosion, felt 25 miles away, on a buildup of combustible gases that ignited.
The report also found that nitrocellulose, a flammable solid, was stored on the site without a license.
Four non-criminal citations were issued to the companies, with fines totaling $800.
A non-criminal citation was also issued to the plumber who installed two oil tanks at the site without a permit, with a fine of $100.
Neither company immediately responded to requests for comment.
The report also made three recommendations to prevent similar incidents, including legislation governing chemical processing safety; better cooperation between licensing and fire and building permitting authorities; and improved inspections of chemical storage facilities.
''One of our main objectives is to learn from this tragedy,'' Fire Marshal Stephen Coan said. ''Today we present not only our findings in the