Shock Absorbers in Dual Main Rope Systems

In the world of rope access, technical rescue, and industrial work-at-height, the adoption of dual main rope systems has become a gold standard for redundancy and safety. Yet, as systems become more robust, the nuances of energy management — particularly through the use of fall arrestor shock absorbers — are often overlooked. This blog addresses a critical question: When are shock absorbers necessary in a dual main rope system, and why?

Why Shock Absorbers Matter in Redundant Systems

A dual main system provides two independently tensioned ropes to support a load or worker. While this setup reduces single-point failure risk, it does not eliminate the dangers of dynamic falls or unexpected shock loading. That’s where fall arrestor shock absorbers enter the picture.

These small, often underestimated components are designed to dissipate kinetic energy during a fall, reducing peak force on the harness, anchor, and rope system. But they aren’t always required — and misuse can even compromise efficiency.

Understanding the Fundamentals

Before diving into application, it’s essential to define the key concepts:

• Fall Arrestor Shock Absorbers: Devices that limit force transmission by absorbing energy during a fall.

• Dual Main System: Two parallel primary lines intended for load sharing and redundancy.

• Fall Factor: A measure of fall severity (fall distance ÷ rope length available).

• Redundancy: The practice of having multiple backups in case one element fails.

Each of these concepts plays into the decision-making framework for whether a shock absorber is necessary in a given setup.

Situational Assessment: When Are Shock Absorbers Needed?

Shock absorbers aren’t universally required in dual main systems. Their use must be based on context and risk assessment. Consider these core factors:

1. Risk Environment

• Are edge transitions sharp or uncontrolled?

• Is a fall of any significant distance possible?

• Is the terrain dynamic, vertical, or exposed?

If any of these are true, force management becomes more critical.

2. Standards and Compliance

Different regulatory standards offer varied guidance:

• ANSI Z359 and ANSI Z459 may mandate shock absorbers depending on system type and use-case.

• Work-at-height policies often require energy-absorbing lanyards or fall arresters in environments with a fall factor above 1.

Understanding what your team is bound to legally and contractually is as vital as knowing what’s technically possible.

3. Load and System Behavior

Even with two lines, if one line is more tensioned or friction-restricted than the other, shock force may not be shared equally. This means the “backup” line may suddenly catch a load — essentially becoming a single main under shock conditions.

• Without shock absorbers, this event can overload anchors or harness connections.

• With them, the load is controlled and distributed more evenly.

Integrating Shock Absorbers into System Design

If a shock absorber is warranted, placement and compatibility matter:

• Install between the harness and the device (or anchor point) to reduce force to the user.

• Verify rating compatibility with the rest of the system — including carabiners, lanyards, and harness connection points.

• Ensure unobstructed deployment space: if the absorber activates, it will extend under load.

Regular inspection is non-negotiable. Shock absorbers degrade over time, especially in environments with moisture, UV exposure, or particulate buildup.

Making the Decision: A Logic-Based Framework

To help determine if you need shock absorbers in your system, ask:

• Is there any chance of a fall with slack in the system?

• Are you operating near edges or potential cut points?

• Does your system have true dual-tension (not just dual-anchor) configuration?

• Do applicable regulations require fall arrest capabilities with energy absorption?

If “yes” to any of these, a shock absorber should at least be considered, if not mandated.

Case Snapshot: What Happens Without One?

In a utility tower rescue simulation, a technician operating with dual main lines (but no absorbers) fell roughly 1 meter during a re-anchor maneuver. One line slipped through a descender, while the second line caught abruptly. The peak load spiked above 10 kN — enough to damage the rope sheath and stress the anchor bolts. Had a shock absorber been integrated, the load peak could’ve been halved, and equipment integrity preserved.

Common Misconceptions

Let’s clear up some confusion:

• “I have two ropes, so I don’t need absorption.” False. Two ropes can’t prevent force; they only provide backup.

• “I’m only going a short distance.” Even short falls can be violent if the rope is static or taut.

• “Energy absorbers complicate the system.” They might, but safety isn’t always about simplicity.

Closing Thoughts

Shock absorbers aren’t just accessories — they’re force management tools. In dual main rope systems, they serve as a safeguard against uneven tensioning, dynamic loads, and human error. While not always required, their thoughtful integration into the system can be the difference between a clean catch and catastrophic failure.

Review your systems. Revisit your assumptions. Train with real-world dynamics in mind.

The best system is the one that anticipates failure before it happens — not after.

Peace on your Days

Lance