What must the CNG service hose be protected from?

The correct answer highlights the importance of protecting the CNG service hose from fretting and extremely high heat. Fretting refers to the wear that occurs when there is relative motion between materials in contact, which can compromise the integrity of the hose over time. This wear can lead to leaks or failures that pose safety risks in the handling and transport of compressed natural gas.

Additionally, extremely high heat can cause the materials used in the construction of the service hoses to degrade or even fail. CNG hoses are designed to withstand certain temperatures, and exposure to excessive heat can lead to deformation, loss of flexibility, or rupturing, ultimately creating a hazardous situation.

While the other options mention valid considerations—such as mechanical damage referring to physical impacts and electrostatic discharge impacting electrical properties—they do not encompass the critical vulnerabilities of fretting and high heat that can directly compromise the hose's functionality. Water and moisture can be a concern for specific applications, but they are not as critical to the CNG service hose's integrity as the threat posed by high heat and fretting. Thus, focusing on the prevention of these two factors is essential for ensuring the safe operation of CNG systems.