What is the minimum height at which a guardrail system must protect employees from falling?

The correct answer is based on regulations outlined by the Occupational Safety and Health Administration (OSHA), which specify that a guardrail system must be in place to protect employees from falling when working at heights of 6 feet or more in general industry settings. This requirement is established to ensure safety and minimize the risk of injuries from falls, which can be severe and often lead to serious harm or fatalities.

In the context of construction environments, the requirement for guardrails may vary. However, for general workplace safety, the threshold for requiring a guardrail system remains consistently set at 6 feet. This height is recognized as a critical point where the risk of falling increases significantly, necessitating the implementation of protective measures.

The other choices do not align with the standard set forth by OSHA for general industry work. While each of those heights may be relevant in different contexts or specific regulations, they do not meet the widely accepted safety threshold established for guardrail systems.