When talking about fall protection which rule applies?

There are several heights at which employees must be protected.

• The four foot rule: If you are doing general industry type work, such as storing lumber or other supplies at your company’s warehouse, the general industry regulations require some type of fall protection (guardrail, personal fall arrest, etc.) for any wall opening or unprotected edge that is four feet or more above a floor or ground level.
• The six foot rule: For construction activities, Subpart M of the construction regulations (fall protection) says that employees working on unprotected sides and edges; leading edges; in hoist areas; around holes; on formwork and reinforcing steel; over excavations; and other situations where the employee could fall six feet or more must be protected by a fall protection system. The fall protection rule also says that for scaffolds; certain cranes and derricks; steel erection activities; certain tunneling operations; construction of electric transmission and distribution lines; and stairways and ladders; the six foot rule doesn’t apply. For these situations, you need to go that OSHA regulation for the fall protection requirements.
• The ten foot rule: For scaffolding, it is pretty straight-forward. The rule says: Each employee on a scaffold more than 10 feet above a lower level shall be protected from falling to that lower level. Guardrail, and personal fall arrest systems are the primary fall protection methods. This rule is consistently one of the most violated rules by construction companies each year.
• The fifteen foot rule: For steel erection, deckers in a CDZ and connectors must be protected at heights greater than two stories or 30 feet. Connectors between 15 and 30 feet must wear fall arrest or restraint equipment and be able to be tied off or be provided another means of fall protection. All others engaged in steel erection at heights greater than 15 feet require fall protection.