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WCB Standards

WCB Standard: G608 Mobile Equipment Roof Structures - Heavy Duty, 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 mobile industrial or logging equipment where the operator may be exposed to hazards caused by falling objects such as tree trunks, snags, limbs, rocks, etc. It is also supplementary to G602 Standard for Log Loader and Log Yarder Raised Cabs.

1.2. Purpose
This standard is intended to describe the minimum requirements for the design and selection of plates and stiffeners for roof construction. Refer to the aforementioned G602 Standard for details on substructure construction.

2. Design Criteria

2.1. Option One - Testing Method
The roof shall be designed to meet the Minimum Performance Criteria for Falling Object Protective Structure (FOPS) - SAE J231.

2.2. Option Two - Analytical Methods
The roof shall be designed to absorb 11500 J (8,500 ft-lb) of impact energy without allowing a projectile measuring 20 cm (8 in) in diameter to penetrate into the DLV as defined in SAE J397a.

2.3. Option Three - Minimum Recommended Size
The roof shall be designed in accordance with the minimum recommended size as outlined in §4.0.

3. Design Requirements

3.1. Superstructure of Roof
The superstructure shall be designed in accordance with the design criteria as outlined in §2.0.

3.2. Substructure of Roof
All frame members and supports of the Cab Protective Structure shall be designed to resist the applied load in accordance with G602. This applies to all mobile equipment covered by G602. Equipment covered by SAE J1040 shall be designed in accordance with SAE J1040 or its equivalent.

3.3. Alternate Exit
The operator protective structure shall be provided with an alternate exit. Such exit shall have a minimum clear opening of 60 cm (24 in) diameter.

3.4. 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:

  • CSA G40.21 33G, 44W - for plates, bars and angles
  • CSA G40.21 50W - for HSS (Hollow Structural Sections)

3.5. Weldments
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.

4. Minimum Recommended Sizes

4.1. Option One - Plate Method
The following are designed on the assumption that stiffeners will be used to limit the unstiffened areas not to exceed 700 sq. in. (4516 sq. cm)

4.1.1
Minimum thickness of roof plate shall be 3/16 in. (4.76 mm)

4.1.2
Minimum section modulus of stiffeners used shall be 0.19 in3, (3.11 cm3) i.e. L 2 x 2 x 3/16

4.2. Option Two - Grid Method
Minimum rod size shall be 3/4 inch round bars or 5/8 inch square bars. Each grid opening shall not be greater than 413 cm2 (64 square inches.) A light gauge roof plate is recommended in conjunction with the grid.

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