Plenum optical fiber raceways must be listed as having what characteristics regarding fire safety?

Plenum optical fiber raceways are required to have ample fire-resistance and low smoke-producing characteristics due to the critical nature of safety in plenum spaces. These areas often serve as pathways for air circulation in heating and cooling systems, making it essential that any material used does not contribute significantly to the spread of fire or the generation of toxic smoke.

Materials that exhibit good fire resistance ensure that they can withstand high temperatures without igniting easily or propagating flames. Low smoke-producing characteristics are crucial because, in the event of a fire, smoke can quickly obscure visibility and significantly affect evacuation efforts. Thus, materials that generate minimal smoke help enhance life safety by reducing hazards during a fire incident.

The other options mention characteristics such as high heat resistance and low smoke, high thermal conductivity and minimal odor, and good flexibility and low cost, which do not comprehensively address both the fire-resistance and smoke-producing criteria critical for plenum-rated materials. Therefore, the best answer emphasizes both the need for ample fire-resistance and a significant reduction in smoke production.