You can choose any pfas provided it meets the osha requirements in section 1926 502 d.
Osha standards for roof access ladders.
For through ladders the steps or rungs are omitted from the extensions and the side rails are flared to provide not less than 24 inches 61cm and not more than 30 inches 76 cm of clearance.
When there is a break in elevation of 19 inches 48 cm or more and no ramp runway embankment or personnel hoist is available employers must provide a stairway or ladder at all worker points of access.
Under the new regulations a ladder over 24 feet high will require a personal fall arrest system or ladder safety system.
Occupational safety and health standards.
For a parapet ladder the access level shall be the roof if the parapet is cut to permit passage through the parapet.
A ladder that is less than 24 feet high does not require a fall arrest system of any sort.
The side rails of through or side step fixed ladders shall extend 42 inches 1 1 m above the top of the access level or landing platform served by the ladder.
Following osha standard strictly could leave you and your company with a liability should an accident occur.
In general the standards require the following.
When a ladder safety system is provided the maximum clearance between side rails of the extension must not exceed 36 inches 91 cm.
Per osha 1910 23 d 4 the side rails of through or sidestep ladders must extend 42 inches above the top of the access level or landing platform served by the ladder.