Final answer:
The top rail of a guard rail system should be 42 inches high, with an allowable margin of plus or minus 3 inches to ensure safety by preventing falls.
Step-by-step explanation:
The top rail of a guard rail system must be within plus or minus 3 inches of 42 inches in height.
When it comes to the safety measures concerning guard rail systems, it's crucial that the top rail is placed at a specific height to provide adequate protection.
In the case of guard rails, the Occupational Safety and Health Administration (OSHA) specifies that the height of the top edge of the top rails must be 42 inches, plus or minus 3 inches, above the walking-working surface. This height ensures that the rail provides a barrier that can help prevent falls from elevated work surfaces.