During the burning of Atlanta when Rhett and Scarlett are heading out of the city, the cameras zoom in on the boxes filled with ammunition. They say, " highly inflammable" not "highly flammable"!
This is not a slip up. "Inflammable" and "flammable" mean exactly the same thing. Namely, they both mean "burns easily." The word "flammable" actually did not start getting used on warning labels until the 1920s, due to the fact that previous labels of "inflamable" caused confusion for the general public. So, during the Civil War, when this movie takes place, the "inflammable" label is accurate.