The minimum height requirement for guardrails varies depending on the specific regulations and the type of scaffold. Here's a summary:

• OSHA (29 CFR 1926):
  • For supported scaffolds manufactured or placed in service after January 1, 2000, the top edge of the guardrail must be between 38 inches (0.97 m) and 45 inches (1.2 m) above the platform surface [1].
  • For supported scaffolds manufactured and placed in service before January 1, 2000, and on all suspended scaffolds where both a guardrail and a personal fall arrest system are required, the top edge height must be between 36 inches (0.9 m) and 45 inches (1.2 m) [1].
  • The height of the top edge may exceed 45 inches if the guardrail system meets all other criteria [1].
• Oregon OSHA (Division 2 & 3):
  • The top edge height of top rails or equivalent guardrail system members must be 42 inches (107 cm), plus or minus 3 inches (8 cm), above the walking-working surface 2, 4, 11.
  • The top edge height may exceed 45 inches (114 cm), provided the guardrail system meets all other criteria [2].
• Saskatchewan Regulations:
  • The horizontal top member must be not less than 920 millimeters and not more than 1070 millimeters above the working surface [3].
  • For guardrails installed on or before October 30, 1988, the height must be not less than 900 millimeters nor more than 1 meter above the working surface [3].
• New Brunswick Regulations:
  • A guardrail shall have a height of not less than 900 mm or more than 1.07 m from the floor level [4].

It is important to consult the specific regulations applicable to your location and type of work to ensure compliance.