Hazardous polymerization

Polymerization is the normal basis of plastics manufacture, but in a controlled reactor the heat is removed. In a storage drum, the same reaction can run away, because heat speeds the reaction and the reaction creates more heat. Monomers such as styrene, vinyl chloride, acrylic acid and some acrylates are examples that can polymerize under the wrong conditions.

Triggers include heat, sunlight, contamination with metals, acids, bases or peroxides, and loss of an inhibitor. Suppliers usually add a stabilizer to prevent the reaction, but stabilizers are consumed with time or can depend on a little dissolved oxygen, so long storage and inert blanketing can be a problem.

Controls focus on keeping the product within the supplier's temperature range, observing shelf life, avoiding contamination and keeping stock rotation in order. Never heat a frozen monomer drum casually, as this can create hot spots without inhibitor. Instructions on thawing come from the supplier.

Signs of trouble include rising container temperature, bulging, hissing, or thickening of the contents. These are emergencies: move people away and call for help rather than trying to cool or open the container.