Which aspect is NOT a requirement for lifeline cords in a mining environment?

The requirement for lifeline cords in a mining environment focuses heavily on safety and visibility. Regarding the material being lightweight, while it can be beneficial for ease of handling and installation, it is not a fundamental safety regulation compared to the other choices. In contrast, flame resistance is critical to prevent fires and protect miners in hazardous environments. This attribute ensures that the cord can withstand high heat and potential flames common in mining incidents.

Reflective markers every 25 feet enhance visibility, allowing miners to locate the lifeline easily in low-light conditions. Directional indicators that do not exceed 100 feet help ensure that the lifelines are effectively laid out for navigation, providing clear guidance without excessive distances that could lead to confusion or misdirection in an emergency. Therefore, the emphasis on flame resistance, reflective marking, and directional indicators is rooted in enhancing safety and operational efficiency, while the lightweight nature of the material, although beneficial, does not specifically align with essential safety requirements.