OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 9 Fall Protection

Section 152 Anchor strength – permanent

Anchors used for attachment of a personal fall arrest system must have a minimum breaking strength of

(a) at least 16 kN (3600 lbs) per worker attached, in any direction required to resist a fall, or
(b) two times the maximum arresting force per worker attached, in any direction required to resist a fall.

The required anchor strength required by this edition of the OHS Code was reduced from the previous 22.2 kN (5000 lbs) to the present 16 kN (3600 lbs) for the following reasons;

(a) with today’s equipment, lower forces are readily achievable;

(b) most jurisdictions in Canada use a lesser value;

(c) despite the previous requirement for a 22.2 kN anchor strength, any worker using a self-retracting device (SRD) today is effectively being protected by a fall arrest system limited to a maximum strength of approximately 16 kN. This is the strength of the wire rope used in the SRD, which sets the limit for the entire fall arrest system. The wire rope strength is limited to 16 kN as a compromise between safety and minimizing the weight and bulk of the SRD;

(d) the lesser value of 16 kN is used throughout the countries of Europe, in Australia, and New Zealand. The value is incorporated in the legislated standards of these countries; and

(e) a lesser value of anchor strength allows for the use of lighter and smaller anchors (without compromising worker safety). The change in required anchor strength potentially increases the variety of fall arrest solutions available to Alberta workers and employers by opening the Alberta market to products that are otherwise currently unavailable.

As pointed out in subsection 152(2), the 16 kN minimum breaking strength requirement does not apply to anchors installed before July 1, 2009. Anchors installed before this date should be rated to 22.2 kN or twice the maximum arresting force that they will experience.

The requirements of this section apply to anchors used in personal fall arrest system; anchors used with horizontal lifeline systems may require greater strengths and must meet the requirements of subsection 153(1).

Two times the maximum arresting force

The two times maximum arresting force approach to rating an anchor i.e. the 2:1 safety factor approach, is particularly useful in cases where workers must be protected from falling but the structure on or from which they are working, such as a power transmission tower, cannot accommodate the 16 kN minimum breaking strength for anchors. When the two times maximum arresting force criterion is applied using the force limit of 6 kN (1350 lbs) required by subsection 151(3), the required strength of the anchor decreases to 12 kN (2700 lbs).

A fall arrest system using an E4 shock absorber that is approved to the CSA Standard for shock absorbers limits the worker’s weight to 115 kilograms (including tools and personal accessories), and restricts the free fall distance to less than 2 metres during certification testing, is capable of limiting the arresting force to 4 kN (900 lbs). The resulting required anchor strength decreases further to 8 kN (1800 lbs).

This “two times maximum arresting force” approach should only be used in accordance with the manufacturer’s specifications or under the supervision of a professional engineer who can accurately determine the peak forces and the available anchorage strength. If shock absorbers become wet and frozen, peak impact forces can approach 8 KN (1800 lbs).

Users of this approach must realize that using shock absorber arrest force performance to set anchor strength has several important limitations:

(1) the 115 kilogram weight limit can easily be exceeded if a large worker is required to wear personal protective equipment, a tool belt, and carry equipment, additional tools or supplies. This worker may be required to use an E6 type shock absorber which limits maximum arresting force under optimal conditions to 6 kN;

(2) the free fall limit distance of 1.8 metres may not always be practically achieved. Workers often use lanyards having a length of 1.8 metres. Connected to an appropriate anchor located above standing shoulder height, the 2 metre limit can be met. However, if the lanyard is attached at a lower level, the 1.8 metre free fall distance against which the lanyard’s performance was verified is exceeded. The lanyard may be unable to limit the fall arrest to 4 kN; and

(3) fall arrest equipment is used under a variety of environmental conditions. When wet, or frozen after being wet, a shock absorber’s maximum arresting force increases. CSA Standard Z259.11 allows the maximum arresting force of an E4 shock absorber, under these conditions to increase to 6 kN (1350 lbs); the maximum arresting force of a wet and frozen E6 shock absorber increases to 8 kN (1800 lbs). This needs to be taken into consideration as a limiting factor if there is a chance that the shock absorber will get wet or freeze after being wet.

Having all anchors comply with the 16 kN per attached worker option is the preferred choice as there is no confusion as to the strength of the anchor. The second option requires the anchor point to be “designed, installed and used in accordance with the manufacturer’s specifications or specifications certified by a professional engineer”.

For more information

Sulowski AC. Fall-Arrest Systems – Practical Essentials. CSA International, Toronto; 2000.