Final answer:
OSHA standards require the top guardrail to be 42 inches (plus or minus 3 inches) above the working surface to protect workers from falls.
Step-by-step explanation:
The Occupational Safety and Health Administration (OSHA) sets standards for workplace safety, which includes specifications for guardrails to protect workers from falls.
According to OSHA standards for the construction industry, the top guardrail, or top rail, must be 42 inches (plus or minus 3 inches) above the working surface. This height is crucial to prevent workers from falling over or under the guardrail and ensures that workplaces comply with safety regulations to prevent accidents and injuries.