Which safety equipment must be worn during structural firefighting?

Turnout gear is the correct answer because it is specifically designed for the rigors of structural firefighting. This specialized protective clothing includes pants, jackets, helmets, gloves, and other components that provide thermal protection, moisture resistance, and protection against heavy debris and fire hazards. Turnout gear is critical in safeguarding firefighters from extreme heat and flames, as well as from hazardous materials they might encounter during operations within a burning building.

While standard uniforms may provide some level of visibility or identification, they do not offer sufficient protection against the dangers present in a structural fire. Heavy boots, although important for protecting the feet, do not encompass the comprehensive protective capabilities of complete turnout gear. As for breathing masks, they address air quality and inhalation hazards, but relying solely on them without the entirety of turnout gear would leave the firefighter vulnerable to other significant dangers encountered in a structural firefighting scenario. Thus, turnout gear is essential for comprehensive protection in such environments.