September 14, 1990
The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood safety and health hazards, and/or inadequacies of materials, devices, techniques and engineering controls. HIBs are initiated based on information provided by field staff, studies, reports and concerns expressed by safety and health professionals, employers and the public. Information is compiled based on a comprehensive evaluation of available facts, literature and in coordination with appropriate parties. HIBs do not necessarily reflect OSHA policy.
The Boston Regional Office has brought to our attention a potential hazardous situation arising from the remounting of elevating and rotating devices on new vehicle chassis with higher cabs. This modification can cause incomplete retraction of lower arm actuating cylinders resulting in excessive down pressure called overstorage. During a recent OSHA investigation of a boom pedestal failure, it was determined that the system hydraulic pressure, following retraction of the lower boom, exerted a very high force on the pedestal truck chassis frame, thereby causing boom pedestal failure and chassis frame damage.
Elevating and rotating devices manufacturers have advised users of several methods to correct this problem. The simplest method involves slowly lowering the boom to its storage position which allows the hydraulic oil to properly return to its reservoir. Another method suggests adding a limiting device in the hydraulic cylinder to shorten the travel distance of the piston, particularly when the boom is in the stored position. A third method consists of installing a dump/relief valve that is activated when the boom is in the stored position.
Attached is an engineering bulletin from the Holan Company that describes the procedure for mounting aerial devices on trucks. The procedure insures that hydraulic cylinders can be completely retracted when remounted on new vehicle chassis.
Please distribute this bulletin to all Area Offices, State Plan States and Consultation Projects.
HOLAN ENGINEERING BULLETIN NO. 533
DATE: REISSUED 4-90
SUBJECT: Determining height on lower boom storage bracket - All aerial devices
MODELS AFFECTED: All aerial devices ENGINEERING
The same procedure should be applied to any type of support required on aerial devices. Cylinder must be completely retracted in all cases before final height is set.
[Diagram showing support dimensions]
A rubber cushion can be added to the top of the bracket. The thickness of rubber would be subtracted from X dimension before cutting the post height.
This procedure of setting the proper height is required to prevent damage to support or aerial device by applying too much pressure with lower boom lift cylinder if support is positioned too high.
Some cases will require the lower boom being stored with lift cylinder not fully retracted in order to clear interference points on body or cab. A limit slug should be added to the cylinder to prevent the boom from over storage, or a dump/relief valve added to the lower cylinder hydraulics to limit downward cylinder pressure against the storage rest.
CHECKED BY: MARION MUSSER
SUBMITTED BY: LARRY STUBBSBack to Top
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