It's relative compared to cellulose nitrate (ie. guncotton). Cellulose acetate has lower flammability but that isn't saying much. Have a look at the Pathé vid

It's relative compared to cellulose nitrate (ie. guncotton). Cellulose acetate has lower flammability but that isn't saying much. Have a look at the Pathé video of the Hindenburg disaster. The "skin" is clearly on fire.