Leading and Sharp Edges
A leading edge an unprotected edge that is actively or continuously under construction. In other words, any time there is the potential for a lifeline to come into contact with an edge of any material, this could be considered a leading edge application. A key difference in these applications that require a leading edge SRL is that the worker is anchored at foot-level behind them. As a worker walks further away from the anchor point, they are exposed to a potential fall over the edge.
A sharp edge is pretty self explanatory - it is an edge that is not rounded and has the potential to cut most lifelines.
Unique Risks of Leading & Sharp Edges
Increased Fall Distance: Foot-level anchoring increases the distance for fall clearance compared to an SRL anchored above a worker's shoulders.
Lock-Up Speed: A longer fall distance increases the amount of time required to engage the lifeline. When a lifeline accelerates out of its housing at a certain velocity, the self-retracting lifeline engages. When the SRL is anchored at foot-level, the lifeline does not hit the required velocity until the wearer has already fallen a considerable distance.
Increased Fall Arrest Forces: Falling a greater distance increases the potential for a higher impact to the body when the SRL engages.
Higher Potential for Swing Hazards: A longer distance fall can cause a swinging hazard, creating a sawing motion when a lifeline is taut over a leading or sharp edge. This motion compounds the potential danger of a lifeline breaking.
How Does a Leading Edge SRL Help?
There are many situations where an anchor point above shoulder height is unavailable. When foot-level anchoring is required, only a leading edge SRL can be used.
Self-Retracting Lifelines that have been rated for leading edge use include one key component: a shock absorber located above the dorsal anchoring point on a worker's harness. The inclusion of this shock absober is critical.
When a worker falls over a leading edge, a tremendous amount of energy is created and then exerted on the spot where the lifeline comes in contact with that edge. The placement of a shock absorber above the dorsal D-Ring on a harness disperses the energy created by the falling worker before it has the chance to reach the point where the lifeline comes into contact with the edge.
Where the lifeline hits an edge is the most vulnerable point. Stopping the energy/force created by a falling worker before it reaches this spot is a crucial factor that prevents the lifeline from overloading and breaking.
In addition to the shock absorber, SRL-LE's must have steel lifelines (for greater resistance to abrasion) and be rated for LE use by the manufactuer. This means the SRL has gone through what is called dynamic performance testing. To be rated for leading edge use, an SRL-LE is tested by dropping the fall protection device's lifeline over a piece of steel bar with an edge radius of no more than 0.005 inches (five thousandths of an inch) while anchored at foot-level. If the lifeline breaks, is severly damaged, or produces arresting forces outside of a predetermined range, the test is considered a failure.
Wherever there is potential contact between an SRL and an edge, it is best to operate with an abundance of caution and consider it a leading edge.