The burn temperature of a permitted municipal waste incinerator is much higher than the temperature of a burn barrel. Poisons produced readily in the low heat of a burn barrel are destroyed in a municipal waste incinerator. Incinerators also have filters, and other pollution control devices. Studies have shown that significantly higher levels of poison are produced in backyard burn barrels than in municipal incinerators.
EPA Backyard Burning Webpage
MPCA Backyard Burning Webpage