HSE: Industrial rope access - investigation into items of personal ...

3.4 CONTAMINATED ROPE TESTS
A limited number of tests were carried out on sections of rope that had been exposed to
contaminants. The choice of contaminants was based on those which are likely to be routinely
encountered on a work site. Direct contamination such as chemical spills, battery acid and
engine oil were not considered as they are, firstly, easily avoidable and recognisable, and
secondly, already subject to published data. Two contaminants likely to be found on an
industrial work site, and on which little data was available, were studied: rust and bird
droppings.
3.4.1 Rust
Sections of rope were left in a bucket filled with water along with around 1 kg of steel swarf
(metal shavings). After about six months the sections were removed and left to dry. Rust
staining was seen on all the sections. The worst affected parts were then tied up into lanyards
using double overhand knots. These were then tested in the same way as the other knots
described previously. When compared to the double overhand knot tests, tied in new rope, no
additional reduction in strength was found. This does not necessarily mean rust has no effect on
polyamide ropes. The amount of rusting that occurred was limited by the amount of oxygen
dissolved in the water. After some time this was used up and rusting slowed considerably.
Periodically removing the rope, allowing it to dry and then re-immersing it would have resulted
in far worse degrees of rusting. This would also be a more accurate simulation of the conditions
likely to be encountered in rope access. Also, whilst the rust itself may not cause damage, the
iron would form chelates 6 with the organic acids that are likely to be formed in such wetting and
drying scenario. Both the chelates and the organic acids would be very likely to cause
weakening of the nylon fibres. More research in this complex area would be necessary before
any definite conclusions could be drawn.
Rope
brand
Type
Table 4
Strength of rope contaminated by rust
Diameter
(mm)
New rope
Average breaking
force
(kN)
20
Rust contaminated rope
Average breaking force
(kN)
Beal Low-stretch 10.5 18.28 18.34
Edelrid Low-stretch 10.5 19.05 19.47
Marlow Low-stretch 10.5 19.79 19.83
Beal Dynamic 11.0 14.92 14.57
6
CHELATE - a chemical compound whose molecules contain a closed ring of atoms of which
one is a metal atom