All Class I permit holders must have a current copy of _____________ on file at each of their branches.

The correct answer is B, NFPA 54 and NFPA 58.

NFPA 54, also known as the National Fuel Gas Code, sets the minimum safety requirements for the installation of gas piping systems, including those using propane, to ensure safe operation and minimize risks associated with gas utilization. NFPA 58, the Liquefied Petroleum Gas Code, specifically addresses the safe storage, handling, and use of liquefied petroleum gases. For Class I permit holders, maintaining a current version of these codes at their branches is crucial to ensure compliance with safety regulations and industry standards. This helps to ensure that all installations and operations are carried out according to the latest safety practices, which is a fundamental aspect of operating in the propane industry.

The other options, while relating to safety and installation standards, do not apply specifically to propane and its handling in the context of Class I permits. NFPA 70 relates to electrical systems, NFPA 60 deals with the storage of cryogenic fluids, and NFPA 25 addresses the inspection, testing, and maintenance of water-based fire protection systems, making them irrelevant in this specific scenario regarding propane safety regulations and requirements.