Issue 39 October 2021 - Journal - Page 112
Regardless of commonly held perceptions lift
suspension rope failures are rare and when this does
arise causation is more often related to an extraneous
factor or event. We are however regularly asked to
advise in relation to rope condition and other related
problems. In part, this is due to the higher rise installations requiring rope structures without internal self
Non-certified Door Locks
Supply chain integrity has also become a concern in
recent years and not always in relation to the widely
criticised Chinese suppliers. An investigation of a failure of a lift landing gate interlock in which the gate
was opened whilst the lift car, which continued to operate, was absent from the floor. This could too easily
have resulted in a fatality and revealed that a failed
casting differed significantly in form from that in the
design drawings. Inspection of other interlocks revealed further, and more radical, deviations from the
design specification and drawings.
Figure 5 shows a section of a set of suspension ropes
which have developed rouging, a form of fretting corrosion, under which the internal core of a rope becomes dry.When the rope strands and wires distort
under pulley loading, the wires abrade each other
with a subsequent loss of material and rope diameter
characterised in the rouge evident at the rope surface.
These ropes were prescribed for immediate replacement prior to further use of the lift.
Whilst the failure of the first casting arose due to a
fatigue crack, other castings were found to incorporate significant design deficiencies that compromised
the overall integrity of the interlocks. Detailed inspection revealed the presence of cracks in the castings
which had developed as a result of the component assembly process. This differed from the original design
specification and included manual peening of the
ends of a steel pivot pin in order to secure this within
the casting. Stresses introduced in the castings during
the peening of the pivot pins induced cracks in the
cast material. These cracks were located at points at
which the cast components were weakest.
In order that the client’s lifts could be retained in
service whilst compliant replacement components
were manufactured all interlocks were inspected and
the cast components subjected to dye penetrant tests.
Subsequent investigation revealed that the components, which had been manufactured in the UK, had
not been approved under the Lifts Regulations, or for
that matter any definable quality standard, but had
been manufactured under a subcontract, with little or
no quality control or understanding of the regulatory
requirement and the possible hazards and risks that
might arise. The variations to the design and material
specification were undertaken on an ad-hoc basis by
Figure 5 Lift Suspension Ropes & Rouging
The Missing Cam
Upon investigating a serious fall down a lift shaft by a
lift user, an understanding of how the lift moved away
allowing the swing landing door to be opened needed
to be established.
Escalator Step Deflectors
A hazard affecting escalators is that of side-of-step
entrapments due to friction between shoes and the
skirts at the side of the moving steps. A mitigation in
the form of skirt deflectors, usually brushes has been
mandatory in the UK since HSE’s 1983 Guidance
Note PM34 which required that new escalators
installed after 1st January 1984 should be equipped
with these. However, PM34 did not prescribe an
installation method or design, but did require that
retrofitting of skirt defectors to existing escalators
should not in itself cause any further hazard. A
subsequent EC requirement required skirt deflectors
on all new escalators installed after February 2005
and prescribed dimensional requirements for the
application of the deflectors.
It is required that a landing lock for a lift of this age has
two circuits; one to confirm the door has closed and
the other to confirm that the door is mechanically
locked, and the lift can move away. The locking action
is normally performed by an electromechanical cam
mounted on the lift and interacting with the landing
The cam and door lock mechanism was missing so
that when the door lock jammed in an unlocked position, the lift could move away allowing the lift user to
open the door and fall.
Subsequent analysis of the schematic diagrams and control circuits revealed that the electrical capability for cam
and door locked circuits were present but shorted out
so that the cam could be omitted from the design.
The Standard specifies detailed shape and dimension
ranges including the end piece of the skirt deflectors
(which need to be prior to the comb intersection) and
the range of dimensions the deflector is allowed to be
fitted above the step line.
This cost saving ultimately cost the installer a lot more.
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