The Farmington Hills Fire Department in Detroit conducted a test of how real and artificial trees react in a house fire. Three identical rooms were setup and then set on fire in the exact same manner. One room contained a well cared for and regularly watered real tree, the second contained an uncared for (and thus dry) real tree, while the third contained an artificial tree of the type sold by big box stores that was labeled as “fire retardant”.
You can read the original account of the event (which was published in the Spring 2005 copy of the Christmas Tree Journal) here.