Final answer:
Safety tips for using thermal styling irons include recognizing that celluloid combs are flammable, overheating irons can cause damage, and that holding the iron firmly ensures even curls. Testing the iron's temperature on tissue paper is incorrect and unsafe due to its flammability.
Step-by-step explanation:
In the context of safely using thermal styling irons, it is important to recognize safe practices and the incorrect option among those provided. Celluloid combs are flammable is a true statement, especially relevant when working near open flames or heat sources like styling irons, as celluloid can catch fire.
Overheating irons can cause damage is another valid safety tip, since excessive heat can harm both the hair and the styling tool. The recommendation of holding the iron firmly to ensure even curls is also correct, as it suggests control and precision during styling, which can help prevent accidental burns or uneven heat application. However, the statement to always test the temperature of irons on tissue paper is the exception here because tissue paper can easily ignite and is not a safe way to test the temperature of a styling tool. Instead, a safer method to check the iron's temperature is on a piece of cloth that is designed to withstand heat or a specially made heat testing strip from a beauty supply store.