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The latter will include daily
and routine inspections
along with ‘thorough
examination’ by a competent
person in accordance
with specified cyclic time
limits. The interpretation
and implementation of
requirements of LOLER are
quite detailed and specific,
so appropriate professional
guidance on them should
be sought by owners and
operators as appropriate.
using an excavator as
a crane – additional
significant hazards
There have been several
health and safety incidents
(or near-misses where
potential incidents were
discovered in time) involving
excavators used as cranes.
The main two types of
hazard are presented by:
1. failure in lifting
accessories; and 2. failure
at the point of connection
between lifting accessories
and the excavator (the latter
may be via a dedicated eye
on a bucket or quick-hitch
for example). When a
failure is catastrophic
– that is, a component
or accessory breaks or
fails totally and without
warning – then the hazards
of falling loads need no
further explanation here.
Of course, these are not
the only hazards. Others
relate to things such as
machine stability during
the lift (especially when
reaching or slewing), other
workers in the machine’s
operational area, use of
incorrect accessories and
work being undertaken by
non-competent persons
(e.g. for slinging and
signalling). However, let
us briefly focus on the
two main hazards relating
to component failure.
failure in lifting
accessories
This would be failure in
an item such as a steel
chain or a nylon strap.
Although wear in the item
might be noticed before
failure occurs, the failure
can often occur without
warning. Typical reasons
for this include the SWL
of the accessory being
exceeded or the presence
of a weakness in the
accessory due to abrasive
damage upon it. In practice,
abrasive damage happens
when an accessory comes
into physical contact
with the load or a part
of the machine, such as
when a lifting sling rubs
against the back of an
excavating bucket.
For multiple slings, failure in
one component places extra
stresses into the remaining
ones and so failure can be
progressive, with typical
results of this being that
the load becomes unstable
and in the extreme, falls.
Principal control
mechanisms to avoid
failure in lifting accessories
include: using accessories
appropriate to the nature of
the work; using accessories
with an appropriate SWL
rating; and slinging /
designing / carrying out
the lift so as to avoid any
physical contact between
accessories and anything
else. A freely suspended
set of straps or chains
attached using a master link
to a dedicated lifting eye
on the machine is optimal.
failure at the point
of connection
The risk here is similar
to the last, where the
connection may make
Figure 1
Diagrammatic
Representation
of Magnified
Stresses
Master link
& quick-hitch
contact
Lifting sling or
chains attached
to load
physical contact with
the machine during the
lift. However, the failing
mechanism is often
different; rather than
occurring as a result of
damage due to abrasion,
the risk is that a component
will become lodged against
the machine and, due
to its configuration, the
stresses imposed within
it become magnified due
to the effects of leverage.
That is, although the
component will have an
adequate SWL for the load
to be encountered, this
magnifying effect causes
stresses far in excess of
this, sometimes by as much
as a factor of 6, 7 or 8
times (depending on the lift
configuration and accessory
size). Catastrophic
failure often results from
this kind of hazard.
A typical example in
practice would be where
an operator moves a quick
hitch about its knuckle joint
(that has a master link and
set of lifting chains attached
to it via a dedicated lifting
eye); to fine-tune positioning
during placement of a heavy
component. If the master
link is trapped against the
quick-hitch, further crowding
causes the furthest part
of the link to now act as a
lever as it moves upward
in an arc. This means that
the load suspended from
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D-shackle through
lifting eye
Quick-hitch with
the attachment
(e.g. bucket)
removed while the
dipper arm is being
used for lifting
As quick-hitch is moved upward, master
link is forced outward and upward
inducing greater forces into it
it magnifies the stresses
within the link’s arms
possibly to the point
that failure will suddenly
occur. Figure 1 shows
this in diagrammatic form.
(The above is but a brief
description of this concept.
For a more complete
explanation with a worked
numeric example, see
the scientific paper by
Edwards and Holt (2010)
listed in the bibliography).
Damage to the
accessories may not
always be catastrophic
– gradual component
degradation
can sometimes prevail.
In such instances, the
‘flattening’ of metal
surfaces might be noticed
in the lifting accessories
(master link for example).
These should instantly
be taken out of service
and the lifting method
redesigned so as to
avoid this contact from
reoccurring.
The principal control
mechanisms to avoid
failure at the point of
connection are as for
failure in lifting accessories
described above, but also
to always ensure that
lifting accessories hang
freely from the lifting eye
and never become lodged
or trapped against the
machine during a lift.
August 2010
19