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| Hazard |
As end-dump truck
bodies and semi-trailer dumping rigs get longer, the incidence of units
tipping over has increased. This type of accident is more frequently connected
with semitrailer rigs than with straight trucks.
In the last couple
of years, one fatality and at least one serious injury have resulted when
dump trucks tipped over. Statistics on the frequency of tip-overs are
not available because the occurrences are not reported unless injuries
result. However, construction personnel involved in dump truck operations
agree that tip-overs are becoming more frequent.
An industry labor-management
committee formed to address this problem strongly recommends that the
construction and trucking sectors become aware of the hazard, the contributing
conditions, and the methods of control set out in this advisory.
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| Stability |
The main hazard is
related to the stability of the end-dump unit when the box is in the raised
position.
When the center of
gravity of box and load is not roughly between the frame rails of the
unit, there is a risk of tip-over (see diagram).
A slight slope can be enough to cause tipping if material sticks in
the top of the box.
Stability is adversely affected by one or more of the following factors:
- the unit is not on a level surface when dumping
- a large amount of material is in the upper portion of the raised box
- material does
not flow out of the top portion of the box, or does not flow out of
one side of the top portion
- the rear wheels
settle unevenly as the load moves to the rear during dumping
- wind may exert
lateral loads, especially if the box is long, as is the case with end-dump
semi-trailers.
Stability may also
be affected by the unit's mechanical condition:
- poor rear suspension
systems on one side of the vehicle
- uneven tire pressures
in rear wheels
- worn or inadequate
components of the lifting system such as pins
- worn or inadequate
lifting cylinders.
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| Hazard Control |
Because of stability
problems with semi-trailers, they should not be used for haulage to rough
grading or fill areas where surfaces are often uneven or loosely compacted.
Straight trucks or straight trucks and pup trailers are more appropriate
for highway haulage to these dump areas. Where haulage and dumping are
all on site, straight trucks or off-highway vehicles are even better choices.
Where aggregates
are being spread for road construction, belly-dump semi-trailers are more
appropriate than end-dump semi-trailers.
Sometimes vehicle
selection is not an option for the contractor. Material suppliers or haulers
do not always use equipment appropriate to a particular site. However,
when contractors do have a choice they should select equipment in accordance
with these recommendations to reduce tip-overs.
Cold weather may
cause materials to freeze to the box and stick when dumping. Using heated
boxes will reduce the problem. During winter, loads should not be left
in dump boxes overnight.
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| Maintenance |
Maintenance can
play an important role in preventing tip-overs.
- Check tire pressures
daily. Tire pressures should be equal on each side of the vehicle.
- Examine and lubricate
pins and bushings regularly.
- Inspect suspension
systems under load to ensure that they work properly and provide even
suspension. Weak suspension systems should be replaced immediately.
- Inspect hoist
cylinders regularly. Worn cylinders should not be replaced with smaller
cylinders or with cylinders rated at lower operating pressure.
- Make sure that
repairs to boxes leave bottom and sides clear and unrestricted. Rough
patchwork repairs near the top of the box can catch and hold sticky
materials.
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| Loading |
Loading of the box
front-to-back must meet allowable gross weight and axle weight limitations
set by the Ministry of Transportation. From side to side it is best to
load as evenly as possible.
If material is likely
to flow poorly, lighten up the load in the top end of the box. A slightly
smaller load will be better than a full load that causes a tip-over.
Box liners will
help most materials flow better during dumping. Liners also help to keep
the box in good condition.
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| Dumping |
Operators should
be trained to recognize areas hazardous to dumping, such as soft or uneven
surfaces and inadequately compacted fill.
Before dumping,
operators should ensure that the tailgate is unlocked and that the vehicle
is on a reasonably level surface. Dumping on surfaces that are not level
is one of the main causes of tip-overs.
Before spreading
material by dumping it from a moving truck, make sure that the entire
length of travel is reasonably level.
Trucks should not
dump when they are parked side by side with another vehicle. When a dump
unit tips over, it is often the operator in the adjoining vehicle who
is injured. Dumping operations should be spread out.
Other personnel
such as dozer operators, surveyors, and spotters should be warned not
to work near a dumping truck in case it tips over.
Workers on foot
should not congregate in areas where dumping is under way.
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