Final answer:
Top rails as per OSHA standards must be 42 inches, plus or minus 3 inches, high above the walkway or working level to provide safety to workers.
Step-by-step explanation:
The question you're asking relates to the safety requirements for construction or similar work environments, specifically to the height of top rails used in guardrail systems.
In the context of occupational safety and health standards, the required height for top rails, according to the Occupational Safety and Health Administration (OSHA), must be 42 inches, plus or minus 3 inches, above the walkway/working level. This rule ensures that the rails provide proper protection to workers from falling off of elevated work surfaces or walkways.