SWLs for Aerial Ropeways
by Alan Sheehan BE
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Vertical
Rescue is both technical, practical and potentially dangerous. This information
is provided for trained and experienced vertical rescue operators. As the
author has no control over the degree to which the information provided here
is understood or applied, he (nor any organisation with which he is
associated) can accept any responsibility for the results of application of
this information, whether correct or otherwise. While every effort has been
taken to ensure there are no errors in this information, this cannot be
guaranteed, so it remains the reader's responsibility to check and verify
this information before application. DANGER! Vertical activities where rope is used for life
support are dangerous. Serious injury and death may result from
misapplication or errors. Introduction
Aerial Ropeways (flying
foxes, tyroleans, highlines - call them what you will...) are amongst the
most critical rigs for vertical rescue. The geometry of an aerial ropeway
results in loads on the span line and its anchors well in excess of the load
being lifted. This multiplying effect makes it vitally important that the
geometry and construction of the ropeway is such that these loads can be
withstood. Equation 1 below is the
usual formula rescuers use to assess span line tension when constructing an
aerial ropeway. This equation is sufficiently accurate for rescue purposes:
vector analysis shows its accuracy decreases with increasing sag. For sags up
to 25% of the span, the formula is accurate to within 3 per cent. (Note: for sags greater than 25%, a
load sharing pair of mainlines or mainline / moveable redirection rig is
logically safer in the event of, say, an anchor failure.) Load x SpanSpan Line Tension = ------------- (Equation 1) 4 x Sag
Safety
The following safety points must be adhered to when
rigging and operating aerial ropeways:
Safety Factors
The following tables present safe working loads
(weight that can be safely lifted) on an aerial ropeway. The Safety Factor
used is 8: as per Australian Standard AS4142.1 - 1993 Fibre ropes Part 1:
Care and Safe Usage and the New South Wales State Emergency Service's
Vertical Rescue Training Package. Users are reminded to check the Safety
Factor which applies under their legislation and organisation's standards.
The safe working loads in the table apply to the span line rope only:
it is the operator's responsibility to ensure that all anchors, karabiners
and associated equipment are also strong enough to withstand the span line
loads with the appropriate safety factor. The safe working loads in these
tables only apply to nylon kernmantle static life rescue line (and Steel Wire
Rope used only for life support purposes where noted). Safe Working Loads (kgs) for Single Rope Span Lines
Safe Working Loads (kgs) for Double Rope Span Lines
Written by Alan Sheehan BE Land Search Instructor, State Emergency Service Oberon Unit, New South Wales, Australia email: als@ix.net.au |
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Note how much more force in in the rope tension than the
load being lifted. 