At Lapeyre Stair, we often get asked if we manufacture ship stairs or ships ladders. The short answer is no. But what are ships ladders and why don't we manufacture them?
Ship stairs and ship ladders are addressed by both OSHA and IBC. OSHA uses the terms ship stair and ship ladder interchangeably while IBC uses the term ships ladder. There is one key difference between a ships ladder and a ship stair. The difference is in how these steep devices are descended. A stair is always descended face forward in the direction of travel while a ladder is always descended backing down, facing the device. So while ship stair and ship ladder are often used to mean the same thing, technically, a ship stair is descended face forward while a ship ladder is descended backing down. OSHA requires that all ladders between 60 and 90 degrees be device-facing, so any ships ladder that is angled 60 degrees or steeper must be descended backing down.
OSHA defines a ship stair in section 1910.21(b) as: "A stair that is equipped with treads, stair rails, and open risers, and has a slope that is between 50 and 70 degrees from the horizontal." In essence, a ship stair is just a very steep stair. This image below from OSHA 1910.25 - Stairways shows two ship stairs at different angles.
IBC does not specify a requirement for a ships ladder angle. In general, ship stairs with shallower angles near 50-55 degrees can be designed to be descended face forward as true stairs, while steeper angles must be backed down as ship ladders.
Ships ladders are usually used when you do not have enough space for a standard stair. OSHA section 1910.25(b)(8) says that spiral, ship, or alternating tread-type stairs are used only when the employer can demonstrate that it is not feasible to provide standard stairs. Usually the case is space restrictions prohibiting the use of a standard stair.
OSHA and IBC also have minimum tread depth requirements for ship stairs and ship ladders. OSHA defines the minimum tread depth for a ship stair in 1910.25(e)(3) as 4" while IBC defines it as 5." For comparison, an OSHA standard stair tread depth is 9.5" and an IBC standard stair tread depth is 11", so ship stairs have much shorter tread depth than standard stairs.
Which brings us back to the initial question, why doesn't Lapeyre Stair make ship stairs? Many studies have demonstrated that stairs with shortened tread depth pose a major risk for users. In fact it is the #1 design induced risk factor of stairs. The Lapeyre alternating tread stair is designed to have the same steep angles as ship stairs but with up to twice the tread depth. For example, the OSHA and IBC minimum tread depth for an alternating tread stair is 8.5" compared to either 4" or 5" for ship stairs and ship ladders. More tread depth has been shown over and over again to be safer and more ergonomic for users.
Lapeyre Stair is committed to providing the safest, most ergonomic stair solutions for our customers. Alternating tread stairs are safer and more ergonomic than ship stairs, and we make the choice to offer this solution as the safer alternative.