The maximum allowable gap between guardrails depends on the application (e.g., highway safety, pedestrian protection, or industrial use) and the governing standards (e.g., MASH, OSHA, or AASHTO). Below are key guidelines:

1. Highway & Road Guardrails (AASHTO/MASH Standards)

Between Posts: Typically 6 to 8 feet (1.8 to 2.4 meters) for W-beam and thrie-beam guardrails.

Cable Guardrails: Up to 12.5 to 20 feet (3.8 to 6 meters) between posts due to tensioned cables.

Deflection Limits: Gaps must prevent vehicle snagging (MASH requires crash-tested systems).

2. OSHA Standards (Workplace & Fall Protection)

General Rule: Maximum gap of 19 inches (48 cm) between rails to prevent worker falls.

For Construction: Top rail must withstand 200 lbs of force, with mid-rails or mesh if gaps exceed limits.

3. Pedestrian Guardrails (Building Codes & ADA)

Vertical Pickets (Balusters): Max 4 inches (10 cm) gap to prevent child entrapment.

Horizontal Rails: Avoid (can be climbable); if used, gaps must not allow a 4" sphere to pass.

4. Industrial & Machinery Guardrails (ANSI/ISO)

Safety Barriers: Gaps should not exceed 0.5 inches (1.3 cm) near pinch points.

Key Considerations:

Crashworthiness (MASH TL-1 to TL-4): Highway guardrails must meet impact test criteria.

Local Codes: Some regions have stricter rules (e.g., California’s Caltrans standards).

Would you like details on a specific application (e.g., bridge railings vs. warehouse safety)?