OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 41 Work Requiring Rope Access

Section 828 Maximum arrest force, clearance

The behaviour of load components in the system, such as dynamic cow’s tails, load-limiting back-up devices and the extension of the low-stretch rope, can help absorb any forces generated, should there be a limited fall. However, the system generally should be designed to avoid this i.e. it should function as a work positioning system.

Rather than stating a restrictive free fall distance, this section allows a worker to fall an unspecified distance as long as three conditions are met:

(a) the maximum arresting force on the worker is limited to 6 kN – maximum arresting force is the short-duration (milliseconds to tenths of a second), peak dynamic force acting on a worker’s body as the worker’s fall is arrested. The maximum arresting force to which a worker can be exposed during fall arrest in Alberta is limited to 6 kN (1800 pounds-force).

Research studies have shown that the short duration forces that happen during fall arrest are unlikely to cause injury if they act vertically upwards through the buttocks and spine and are limited to no more than 9 kN (2000 pounds-force). The 6 kN limit is therefore considered safe but, as was discovered during the studies, is subject to the following conditions:

(i) the maximum arresting force is applied upwards through the pelvic area;
(ii) the worker’s physical condition is sufficient to withstand such a jolt; and
(iii) the duration of the maximum arresting force is limited to a fraction of a second;

(b) the worker is prevented from striking a lower surface that could cause injury, unless preventing this possibility exposes the worker to other greater hazards; and

(c) the swing-fall hazard is minimized.