You can treat fabrics with flame retardent. The product used depends on the actual material. Flame retardents evaporate and leave a salt behind which hinders flame spread. They will still burn as Chris says but at a slower rate.
They would probably want a certificate which you could only really issue if you had the items tested by the fire brigade. The way round that is to issue a notice stating that the fabric has been treated with such & such which complies with BS blah blah (there are a whole list of regulations which will be listed on the product data).