For horizontal slide gates, what is the minimum guard height above ground to prevent a 2 1/4 inch diameter sphere from passing through?

• A. 6 feet
• B. 4 feet
• C. 3 feet
• D. 2 feet

Answer: (A)

Guard height is set so that a 2 1/4 inch diameter sphere cannot pass through openings around a horizontal slide gate. Using this sphere as a test object means the barrier must be tall enough that, in any orientation or during gate movement, there’s no gap the sphere could slip through. Six feet is chosen because it provides a substantial vertical barrier, ensuring the entire opening around the gate remains too small for the sphere to pass. Shorter heights—four feet, three feet, or two feet—leave lower gaps or misalignment opportunities where the sphere could maneuver through during operation or contact with moving parts. In this context, six feet is the safe minimum that reliably blocks passage of a sphere of that size.