Violations pertain to electrical systems, employee training and combustible dust that was trapped in the ceiling and exploded.
West will pay $100,000 in fines and pay $300,000 to local charities who helped on the day of the explosion.
The Labor Department originally issued $602,000 in fines. West negotiated that down to the $400,000. It is building a new plant in Kinston.
U.S. Chemical Safety Board investigators concluded that a dust explosion occurred above an area where rubber strips were coated with moistened polyethylene powder. Investigators said the five conditions necessary for a dust explosion were all met at the West plant: fuel, oxygen, dispersion, confinement and ignition.
U.S. Chemical Safety Board Chairwoman Carolyn Merritt said, "The dangers of explosive dust are not well known, and helping industry to understand this insidious hazard certainly will be a priority."