Sometimes you don't have enough room for a full size stair, but you don't want to use a 90 degree safety ladder because you want an easier climb. For those instances you can use a ships ladder (sometimes called ships stairs). Ships ladders have a safe climbing angle between 50 and 70 degrees and have ladder safety rails on both sides. Those ladder rails can terminate with the top tread for use as a roof hatch access ladder, or can extend above the top tread like the handrail on a standard stair design.
OSHA fixed ladder requirements do not pertain to ships ladders and neither do OSHA stair requirements. You can see the details in the letter from OSHA below the ships ladder sketch below.
The treads on a standard steel ships ladder are up to 12” apart and 24” wide, but this can be adjusted stair to stair depending on requirements. They can be done as either closed diamond plate stair treads or bar grating treads, but the bar grating tread is the standard option due to its superior slip resistance, self-cleaning design and economic price.
To order a ships ladder we will need to the dimensions of (A) and (B) below. Standard finish is black grating treads and gray stringers and handrail. We can also provide ships ladders in a custom paint color or hot dipped galvanized.
You can find the below letter from OSHA here