Bathtubs made of plastic are required to be manufactured with what feature due to concerns with accidental exposure to a plumber's torch?

The requirement for bathtubs made of plastic to include fire-resistant chemicals stems from safety concerns regarding accidental exposure to heat sources, such as a plumber's torch. When a plastic bathtub is subjected to a high temperature from a flame, it can melt or deform, posing safety risks during installation and use. By incorporating fire-resistant chemicals into the material during manufacturing, the bathtub can better withstand unexpected exposure to heat, thereby reducing the risk of fire hazards and enhancing durability.

This requirement emphasizes the importance of fire safety in plumbing and construction practices, ensuring that home fixtures can endure typical conditions encountered during maintenance or repairs. Other features like waterproof adhesives, reinforced edges, or anti-slip surfaces serve different purposes, such as enhancing adhesion, structural integrity, or safety in terms of slip resistance, but they do not address the specific concern of fire exposure related to plumbing work.