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WCB Standards

WCB Standard: G607 Medium Duty Screen Guard (Front End Log Loader), 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 front end log loaders - mobile machines mounted on a wheeled or tracked chassis, equipped with a front mounted grapple, tusk, or fork-lift device and employed in the loading, unloading, stacking, sorting or handling of logs, used only in dry land sorting areas. For other applications, please refer to G603 Standards for Log Loader and Log Yarder Window Guards.

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 cab.

2. Location of screen guards

2.1.
Front screen guard shall be provided in the area in front of the operator and shall at least extend the full height of all glazing surfaces.

2.2.
Rear screen guard, where necessary and applicable, shall be provided in the area behind the operator.

2.3.
All guards shall be positioned at least four inches away from the glazed windows.

3. Design Requirements

3.1. Strength Requirements
3.1.1 Grid Element
Each vertical element shall be designed to withstand a minimum concentrated point load of 300 lbs. being applied at a location producing the greatest critical stresses. There should be at least three vertical elements.

3.1.2 Perimeter Frame
The outer frame shall consist of sections with the following section modulus:

Perimeter frame modulus in metric and imperial measure 

S = edge beam section modulus (cm3) (in3)
W = dimension of guard (cm) (in)
f = allowable working stress MPa (psi)

3.1.3 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 guards.

On the front end loaders equipped with a rollover protective structure (ROPS), the screen guards may be attached to parts of the ROPS, provided that such attachment does not adversely affect the performance of the ROPS. All such attachments shall be clamped unless welding is permitted by the ROPS manufacturer or a registered professional engineer.

3.1.4 Fastenings
If nuts and bolts are used in the fabrication of the guard, they shall conform to or exceed the ASTM Designation A325 requirements.

3.2. 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 phosphorous 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 40.21 50W - for HSS (Hollow Structural Sections)

4. Visibility Requirement
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. The clearance between vertical elements shall not be greater than eight inches.

5. Minimum Recommended Sizes

  • Vertical elements cross-section size should not be less than 19 mm (3/4") diameter mild steel rod or 16 mm (5/8") square rod.
  • The openings between adjacent vertical members should not be greater than eight inches.
  • The perimeter frame cross-section size should not be less than 2 x 2 x .150 square hollow structural section (HSS) 50,000 psi yield or 3 x 3 x 5/16 square angle, 36,000 psi yield.

6. Weldment
Weldments shall conform to applicable sections of General Specification for Welding of Steel Structures, CSA W59.1-1970 (or latest revision thereof) and shall be performed by licensed welders only.

Illustration - Weldment Typical Design

Typical Design
For Illustration Only

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