What must be posted in areas accessible to persons other than the operator during welding and cutting operations?

The correct answer involves the need for clear communication regarding the potential hazards associated with welding and cutting operations. Posting conspicuous signs that warn "Caution - Hot Work in Progress - Stay Clear" is essential for ensuring the safety of individuals who may enter the area. These signs serve to alert anyone nearby about the ongoing operations, which may involve high temperatures, sparks, and possible toxic fumes, thus minimizing the risk of accidents or injuries.

In environments where welding and cutting take place, the nature of the work creates specific dangers that can affect those who are not actively involved in the operation. Therefore, having a prominent warning sign helps to maintain awareness and encourages individuals who are not operators to keep a safe distance, thus protecting them from hazardous conditions.

The other options do not adequately address the specific requirement of warning nearby persons about the ongoing hot work. While no entry signs might restrict access entirely, they may not inform individuals about the hazards they face. General safety signs might provide some information, but they lack the specificity about the ongoing operations. Similarly, signs indicating protective equipment required could inform operators, but they do not serve to warn other individuals who might inadvertently enter the work area.