The Guardian Fall Team Blog

In August of 2012, ANSI, in their Z359.14-2012 Safety Requirements for Self-Retracting Devices for Personal Fall Arrest and Rescue Systems (since revised to Z359.14-2014), divided SRLs into two classes. These classes are defined based on an SRL’s maximum potential arrest distance and maximum potential average arrest force. SRLs with a maximum arrest distance of 24 inches are labelled Class A, and those with a maximum arrest distance of 54 inches are labelled Class B. Average arrest forces are capped at 1,350 lbs. for Class A SRLs, and 900 lbs. for Class B SRLs, with the maximum arrest force of 1,800 lb. for both classes.

Breaking It Down.

Going only by the numbers, it seems no matter which SRL you choose you will be trading arrest force for arrest distance. On its face, that’s true. But if we take a more nuanced look into the real-world meaning of those numbers, it becomes clear that what seems like a compromise is actually a means to provide the most appropriate solution for a given fall protection scenario.

First, it’s important to understand that both classes of SRLs are OSHA 1926.500 subpart M compliant because they both, “limit [the] maximum arresting force on an employee to 1,800 pounds (8 kN) when used with a body harness.” This means that no matter what class of SRL you choose, you can rest assured of OSHA compliance. When it comes to the difference in average arresting force between the two classes (1350 lb. and 900lb., respectively) it is really just a by-product of how quickly the SRL stops a fall.

SRL Classes Explained - Guardian Fall Protection

Think about it this way: if I tie a rope to a boulder and toss it off a bridge, then tell you to stop the boulder in 24 inches, the average arresting force exerted on the boulder (and your hands) will be a heck of a lot higher than if I gave you 54 inches to stop it. The more distance you have to stop the falling boulder, the more time you have to spread out the arresting force and keep it from peaking suddenly. Same goes for stopping a car: slam on the brakes going 65 and you feel a lot more force than slowly applying your brakes over half a mile.

Why have classes at all…and why do I need a calculator?

In a nutshell, it’s not a one-size-fits-all world. Each fall protection scenario is different and requires the proper solution to, well, keep you from reaching bottom, as it were. The single most important factor in determining which class SRL you should use is Fall Clearance. Fall Clearance is the TOTAL calculated distance required to stop a fall in addition to a 3’ safety factor. (For a bit more on Fall Clearance, have a look at the instructions for our Diablo Class A SRL).

If your calculated Fall Clearance is only 7 feet and you have a Class B SRL, you will only leave yourself with about a 1’ safety factor – this isn’t enough. In this scenario, a Class A SRL would be the correct choice because of its shorter arrest distance. Even with the slightly higher average arrest force of the Class A SRL, the choice between it and the alternative is a no-brainer.

ANSI safety requirements aren’t arbitrary. ANSI engineers don’t sit around the lunch table telling jokes and making up regulations just for fun. OK, maybe it is fun for them, but in the end their work is serious, and when ANSI creates a regulation, such as making a distinction between SRLs based on maximum arrest distance and average arrest force, it’s for a good reason. We go home to them every night.