4. The methomyl-solvent mixture was fed to the residue treater before the residue treater was pre-filled with solvent and heated to the minimum safe operating temperature.
5. The incoming process stream normally generated an exothermic decomposition reaction,
but methomyl that had not crystallized due to equipment problems greatly increased the
methomyl concentration in the residue treater, which led to a runaway reaction that
overwhelmed the relief system and over-pressurized the residue treater.