According to the FRA, what action is required for a rail with a torch cut end used in classes 3 - 5 track?

The correct answer is rooted in safety regulations outlined by the Federal Railroad Administration (FRA). A rail with a torch cut end presents a serious structural integrity concern, particularly in classes 3 - 5 track, where the operational demands are significant but not as severe as in higher classes. Such torch cut ends can lead to issues like stress concentration, which may compromise the rail's ability to safely support trains.

In non-emergency situations, the use of such rails is prohibited due to potential risks that could affect both the integrity of the track and the safety of railway operations. The restriction placed on using these rails ensures that only those rails that are fully intact and comply with safety standards are in service.

In contrast, the other options do not sufficiently recognize the risks associated with using torch cut rails. Allowing their use without conditions could lead to safety hazards; suggesting that they should always be used demonstrates a lack of acknowledgment of the context. Likewise, recommending immediate replacement or painting for visibility does not address the primary concern of integrity and safety associated with such rails. Thus, the requirement is clear: no rail with a torch cut end should be used except in emergencies, reflecting the utmost priority placed on safety.