In the US, the American's with Disabilities Act (ADA) specifies a maximum slope of 1:12, complete with handrails (any slope over 1:20 to 1:12 requires the full ADA treatment unless the ramp is 6: in height or less):
https://www.access-board.gov/guideli...and-curb-ramps
If you can get the slope to 1:20 or less, then ADA doesn't consider it a ramp and no handrails are required.