A passenger was told he couldn't bring his table tennis ball on board the train during security check because it was made of the flammable solid celluloid material.
However, there is another type of table tennis ball made of environmentally friendly cellulose acetate, with a melting point of over 200 degrees Celsius, which can be transported by rail.
Differentiating between the two materials is simple: balls marked with "40+" are made of the newer, safer material, while those without markings or marked as "40" are the prohibited celluloid material.