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WCB Standards

WCB Standard: G603 Log Loader and Log Yarder Window Guards, March 1990

© Workers' Compensation Board of British Columbia. All rights reserved. No part of this document may be copied, reproduced, or distributed for profit or other commercial enterprise, nor may any part be incorporated into any other publication, without written permission of the Workers' Compensation Board of B.C.

1. General

1.1. Scope
This standard pertains to log loaders and log yarders, and other mobile equipment where the operator is exposed to the hazard of intruding or flying objects, such as snapped or whipping cables, loose debris and tree limbs. It is supplementary to other WCB Standards for operator's guards:

The scope and guidelines of each of the above standards shall be correctly interpreted and proper judgement made in determining their appropriate application.

For front end log loaders which are used exclusively in dry land sorting areas, refer to:

1.2. Purpose
This standard is intended to describe the minimum requirements for the design and selection of rod-size, framework and supports for guards over window areas of operator's cabs. It may also be applicable to other openings such as doorways in certain circumstances.

2. Design Requirement

2.1. Strength Requirements
2.1.1 Grid Element

Grid element sizes and construction shall be designed to withstand a minimum concentrated point load of 666 lbs., (2,963N) working load being applied at each of the four corners of any grid opening, with the critical stresses calculated as a function of the dimensions of the guard.

2.1.2 Edge-beams (Perimeter Frame)
The outer frame shall consist of sections with the following section modulus:

S > 14.9 x
W Metric Units For the horizontal edge beam.
S > 333 x W Imperial Units
S > 14.9 x L Metric Units For the vertical edge beam.
S > 333 x L Imperial Units

S = edge beam section modulus, (in3, cm3)

W = width of guard (in, cm)

L = length of guard (in, cm)

f = allowable working stress (MPa, lb/in2)

2.1.3 Supports
The perimeter frame shall be secured to the structural parts of the cab. Such structural parts shall be adequately designed and constructed to resist all loads imposed on them by the Guard.

2.1.4 Fastenings
If bolts and nuts are used in the fabrication of the guard, they shall conform to or exceed the ASTM Designation A325 requirements, or conform to SAE Standard J429 and J995 grade designation 5 through 8.

2.2. Impact Strength Requirement
All members of the guard shall be made of material with good impact absorbing properties. The following guideline may be used:

  • Low carbon content (less than 0.28%)
  • High ratio of manganese to carbon
  • Low phosphorus content
  • Fine grain size
  • Heat treated
  • High ultimate energy resistance

Examples of steel meeting or exceeding the above requirements:

  • ASTM A36, CSA G40.21 33G, 44W - for plates, bars and angles CSA G40.21 50 W - for HSS

2.3. Visibility Requirements
Minimum interference with operator's visibility shall be one of the governing criteria in the design and positioning of the vertical members of the guard. If flat bars are used as grid elements, they should be in a radiating pattern in line with the operator's line of sight. Each grid opening shall not be greater than 64 square inches (413 cm2).

2.4. Location
Guards shall be installed in front of all window areas exposed to flying or intruding hazards. All guards shall be positioned at least 4 inches (10 cm) and not more than 8 inches away from the glazed windows or exterior faces of the cab.

3. Structural Details

Minimum grid element size shall be 3/4 inches diameter steel rods or equivalent.

Grid element rod sizes shall be proportionately increased as the dimension of the guard increases.

Gusset plates shall be incorporated where the length of the edge beam exceeds three feet.

Minimum edge beam size shall be determined in accordance with 2.1.2 but shall in no cases be less than 2 1/2 inch x 1 1/2 inch x 0.125 inch HSS.

Materials with equal or better properties may be used in place of those stipulated in this Standard.

4. Design Aid

4.1. Equivalent Strength Table

Grid Element


3/4" dia. Mild Steel Rod

7/16" 6 x 19 IWRC Wire Rope*

7/8" dia. Mild Steel Rod

1/2" 6 x 19 IWRC Wire Rope*

1" dia. Mild Steel Rod

5/8" 6 x 19 IWRC Wire Rope*

4.2. Typical Design
Overall Dimension: 44" x 44"

Grid Element

X-Section Size:

3/4" dia. Mild Steel Rod

7/16" 6 x 19 IWRC Wire Rope

Edge Beam

3 x 3 x 5/16 Angles ASTM A36 or CSA G40.21-33G

2 x 2 x .125 HSS
(50 ksi yield)
CSA G40.21
(40.16 and 40.17)

* Wire Rope may be considered as equivalent provided they are adequately anchored and tensioned. (See illustration attached).

G603 Illustration of Typical Design

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