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WCB Standard: G604 Light-Duty Screen Guards For Off-Highway Equipment, 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 equipment such as tractors, loaders, skidders, where screen type guards are required to protect operators against flying or intruding objects. The guards are intended to resist the penetration by flying or intruding objects or materials into the critical zone which is defined as the Deflection Limiting Volume (DLV) in the SAE Recommended Practice J397a for off-highway equipment.

1.2. Purpose
This standard is intended to describe requirements for the design of supports and framework, and selection of screen material pertaining to light-duty screen guards.

1.3. Terminology and Illustrations *

1.3.1
For the purpose of this standard, the following definitions shall apply:

"Equipment" includes tractors, loaders, skidders and other types of off-highway equipment where operator protection in the form of light-duty screen guards is both necessary and practical.
"Framework" means the frame consisting of the edge stiffeners and intermediate stiffener(s).
"Screen Guard" consists of screens, stiffeners, and all supporting brackets necessary to secure the Guard to its supports.
"Stiffener" refers to any structural member adding rigidity to the screen. It also serves to transfer loads applied to the screen onto the supports.
"Supports" refer to the structural members supporting the Screen Guard, and are usually part of the ROPS (Rollover Protective Structure).

1.3.2
The illustrations are to clarify the terminology used and not to be construed as model designs.

Please see Illustration 5.

2. Location of Screen Guards

2.1.
Back screen guard shall be provided in the area behind the operator.

2.2.
Side screen guard shall extend forward from the back screen guard to at least the forward edge of the operator's seat and shall extend vertically to at least the full height of operator's control area (ROPS or canopy). The screen should not obstruct or restrict the operator's egress from his control area.

2.3.
Front screen guard, where necessary and applicable, shall be provided in front of the operator's control area.

3. Design and Fabrication Requirements

3.1. Design and Fabrication Requirements for Supports
3.1.1
The supports shall be adequately designed and fabricated to resist all loads that the screen guards would likely impose upon them.

3.1.2
On mobile equipment 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.

3.2. Design and Fabrication Requirements for Screen Guards

3.2.1
The Screen Guard shall resist the penetration by flying or intruding objects or material into the Deflection Limiting Volume as defined by the SAE Recommended Practice J397a.

3.2.2
The screen mesh material should have sufficient flexibility so that the applied load could be distributed over its entire area. Woven, welded wire mesh or other materials of equivalent or better strength properties are acceptable.

3.2.3
The screen mesh shall be fabricated of steel wire material of 6.35 mm (1/4") diameter minimum, having a maximum clear mesh opening of 4.44 cm x 4.44 cm (1 3/4 inch x 1 3/4 inch) square. Such mesh shall be welded to the Framework and should not be welded directly to any ROPS.

3.2.4
The spacing of the edge and intermediate stiffeners should be designed in accordance with the attached "Stiffener Chart."

3.2.5
All free edges of a screen shall be reinforced with stiffeners having a minimum width of 2.5 cm (1 inch) and with the following section modulus:

Section Modulus

Where S = applicable section modulus which shall not be less than .82 cm³ or (.05 in³), based on
fy = 36 ksi, 250 Mpa
L = unsupported length (in) or (cm)

3.2.6
All intermediate stiffeners, where used, shall have a section modulus as recommended in 3.2.5.

3.3. Minimum Design Criteria
The following design criteria may be used in lieu of the recommended sizes and dimensions:

3.3.1
Any area of the screen shall be designed to resist a 18,000N (4,000 lb) static force applied over an area of 62 cm², (9.6 in²).

3.3.2
The screen deflection shall not exceed the limits set by Deflection Limiting Volume per SAE Recommended Practice J397a.

4. Impact Strength Requirements

All components of the Screen Guard and Supports shall be made of material with good impact absorbing characteristic which is assisted by:

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

Examples of steel meeting or exceeding the above requirements:

ASTM A36, A500, A501, A618, CSA G40.21 Grade 33G, 42W, 50W, 55W

Attachments:

Chart
Sample Designs
Illustrations

Stiffener Chart

APPENDIX G604 SAMPLE DESIGN

Example: To guard a 32" x 48" area against flying or intruding object.
Screen Material Selection
Choose 1/4" x 2" woven steel wire, (1 3/4 x 1 3/4 clear openings)
Framework Design

1. Spacing of Stiffeners (See Stiffener Chart)
Since 48" is the longer dimension, project horizontally along Lu = 48" until the line intersects with 1/4" x 2" woven mesh curve. Project down and read corresponding Wu which is 19".

G604 Sample Design

Alternate Design
Lu = 32
From Chart Wu = 20 < 24 that is required. Not OK.
Increase wire mesh size to 1 ga.
Wu = 38" > 24" OK.

2. Selecting Edge and Intermediate Stiffener Size (3.2.4)

a. Horizontal Edge Stiffener (members No. 1, 2, 3, 4)

b. For Intermediate member (member No. 7)

c. For Vertical Edge Member (members No. 5, 6)

For simplicity in fabrication, use 1" dia. x .125 HSS (Hollow Structural Sections) round, 0.127 in³ for the entire frame.

APPENDIX II. RECOMMENDATION

Protective screens installed under this Standard will not provide complete protection for equipment operators who are sometimes also exposed to such hazards as flying jaggars or other injurious particles which may be projected through the openings of such protective screens. Where such additional hazard exists, it is recommended that the operators be further protected from such flying or intruding objects by the provision of transparent protective shields so mounted on the screens that they can be readily accessible for cleaning without undue impairment to the operator's vision. The grazing materials used in the make-up of the protective shield should have such properties as good luminous transmittance, cleanability and resistance to abrasion, impact, solvents and weather conditions. An example of a plastic meeting the above requirement is Lexan MR 4000 or MR 40T4.

July 24, 1975

ILLUSTRATION I - Example of an "acceptable" screen framework. This framework consists of .150 x 1-1/2 O.D. HSS Round, and is independent of the ROPS.
[Original graphic currently not reproducible. For a paper copy, please contact the Engineering Department of WCB of B.C. at (604) 276 -3114.]

ILLUSTRATION 2 - The side and back screens are made of 1 ga. x 2 woven wire mesh. Intermediate supports have been added to conform to the standard G604. Nominal sizes are: 32" x 22", 32" x 16", (side screens), 32" x 10", 32" x 38" (back screens).
[Original graphic currently not reproducible. For a paper copy, please contact the Engineering Department of WCB of B.C. at (604) 276 -3114.]

TYPICAL SIDE SCREEN GUARD ASSEMBLY

ILLUSTRATION 3 - View from "protected" cab.
[Original graphic currently not reproducible. For a paper copy, please contact the Engineering Department of WCB of B.C. at (604) 276 -3114.]

ILLUSTRATION 4
EXAMPLE OF "WHAT NOT TO DO"
The mesh should not be welded directly to the structural part of the ROPS. Please note the structure shown is not a ROPS.
[Original graphic currently not reproducible. For a paper copy, please contact the Engineering Department of WCB of B.C. at (604) 276 -3114.]

ILLUSTRATION 5
For Terminology Clarification
[Original graphic currently not reproducible. For a paper copy, please contact the Engineering Department of WCB of B.C. at (604) 276 -3114.]

APPENDIX III. ALTERNATE FOR LIGHT DUTY SCREEN

Illustration - Alternate for Light Duty Screen

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