OSHA Hazard Information Bulletins
September 14, 1990
| MEMORANDUM FOR: |
REGIONAL ADMINISTRATORS |
| FROM: |
THOMAS J. SHEPICH
Director
Directorate of Technical Support |
| SUBJECT: |
Hazard Information Bulletin on Vehicle-mounted Elevating
and Rotating Devices |
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.
Attachment
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
REMARKS:
1) The lower boom lift cylinder must be completely retracted.
2) Measure height of lower boom at point of support from bottom of post ("X" dimension see sketch)
3) Cut post height to X dimension measured on lower boom
4) Add support bracket (1/2" bracket will provide enough down pressure
to hold boom.
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 STUBBS
|
Back to Top
Printing Instructions