Polypropylene Rope Hazard Alert

Summary

Untreated (against UV deterioration), polypropylene rope may lose all of its capacity to carry payload due to its peculiar mode of aging. This aging process is greatly accelerated by the ultra-violet spectrum of sunlight. When used outdoors, such rope eventually becomes brittle with single filaments fracturing easily, and in extreme cases, becoming powdery. Long before this stage of deterioration, such polypropylene rope is unfit for use. On the other hand, polypropylene which was treated with UV inhibitors at the stage of pellets production in a chemical plant may have performance characteristics equal to, or even superior to traditional nylon and polyester. This is especially true if such treated polypropylene fibre has been blended with other fibres of the polyamide, aramid or other type. The problem arises from the fact that when looking at such improved polypropylene ropes, one cannot tell the difference between the treated and untreated polypropylene. With the continuing increase in global exchange of products, users of the polypropylene family of ropes must relay entirely on the information obtained from the rope supplier, who in turn may be importing the rope from a country with different rope standards. These standards may require much lower quality assurance procedures than those in the USA or Canada.

Some jurisdictions and some standard writing organizations prohibit use of polypropylene rope for any life saving operations [1].

The Hazard

What is it? The used polypropylene rope which is employed as a vertical lifeline in a Fall Arrest System (FAS) may fail during fall arrest action due to the loss of the rope strength caused by aging. There are documented cases of fatalities involving window washers who prefer polypropylene because it does not absorb moisture.

Why does it exist? This hazard exists because of two factors: one human, and one chemical. The human factor is related to either lack of knowledge of the aging mode of polypropylene ropes, or to attempting to save money by purchasing the cheapest rope. The former results in employing an untreated polypropylene rope as a lifeline usually in Fall Arrest Systems (FASs) with rope grabs aka fall arresters. The rope should be inspected and replaced if necessary before it becomes a high risk rope. The latter is the wrongly perceived saving on the cost of polypropylene rope replacement.

The chemical factor arises from the fact that all C-C bonds (Carbon) in the polymer chain are relatively weak [2] and subsequently “during the process of photo aging, the polymer cracks, becomes brittle...” [3].

Where can you experience it? This hazard exists in Fall Arrest Systems (FASs) with Vertical or Horizontal Lifelines (or both) which employ untreated polypropylene rope and which do not undergo the necessary frequent inspections and replacement of such ropes.

Who is affected by it and when? Window washers are the most affected by this hazard because polypropylene is the preferred lifeline in the window washing trade. The polypropylene rope has an advantage over other fibres because it does not absorb moisture and thus does not swell. This rope is also fairly resistant to mild acids and mild alkalis which may be used for window washing.

How to Eliminate It Or Minimize Its Consequences?

1. Alternatively, either do not use polypropylene rope as a lifeline, or, if used, inspect it frequently for signs of brittleness, filament cracks etc. and replace immediately when such signs of deterioration are found. Follow strictly all manufacturers’ recommendations regarding inspection, service life and replacement of these ropes.
2. Introduce and enforce rope standards which would make treatment with UV inhibitors mandatory at least in those sizes of polypropylene rope which are used as lifelines (5/8" and 3/4" or 16mm and 19mm nominal diameter), or
3. Alternatively, ban the use of polypropylene rope from any life saving applications in which the ability of this rope to float is not a beneficial and required characteristic.
4. Seek additional information about the UV-inhibitors in the fibre from the rope supplier.
5. Provide proper training in fall protection to all users of Fall Arrest Systems (FASs).

Additional Information and Comments

Polypropylene ropes seem to have a legitimate use as lifelines only in the window washing industry, and only if they are UV deterioration inhibited. They should be frequently inspected and replaced at the slightest sign of the loss of strength. Their advantages of non-absorption of moisture and relatively good resistance to chemicals make these ropes attractive for window washers.

Outside the window washing industry, their popularity is most likely related to their low cost. Unfortunately their users are not aware of the polypropylene aging mode which leads to a total loss of strength. There are documented fatal accidents due to this rope failure on impact during fall arrest [6]. In addition to accidents, numerous incidents of materiel damage have been reported, involving very popular 3/8 diameter polypropylene handline. These handlines are known to drop their payload because of the rope’s total loss of strength (and inadequate inspection and replacement policy [7]).

On the other hand, polypropylene ropes made out of filaments made by extrusion from melted pellets, when the pellets supplied by their manufacturer have been treated with UV inhibitors, pigments and other additives, have a resistance to sunlight equal to other synthetic fibres [8].

A polypropylene rope, sold under the trade name Polysteel, which has excellent characteristics, has been available in Canada and the USA since the early ‘90s. This rope is made of multi-filament, continuous (no splices) yarns of co-polymer fibre of polyethylene and polypropylene. It is of 5/8" (16mm) diameter and of twisted, three strand construction. This rope is reported [9] to have excellent resistance to UV, as well as to acids and alkalis. It does not absorb moisture, allowing it to be used and stored when wet. This rope stretches less than nylon, and when new it has approximately the same, high breaking strength.

References

1. “Standard for: Rope, Polypropylene, Monofilament” CGSB Standard 40-GP-13M.
2. “Thermal Degradation of Organic Polymers” Samuel L. Madorsky, John Wiley & Sons, New York, London, Sydney.
3. “Polypropylene. Polymer Monographs” Volume 2, H.P.Frank, Oesterreichische Stickstoffwerke, Gordon and Breach.
4. “Outdoor and Weatherometer Exposure of Polypropylene Ropes”, David A. Black, Research Report No. 76-459-H, Unpublished. Ontario Hydro, Research Division, 1976, Toronto.
5. “Factors Affecting Light Resistance of Polypropylene” McTigue, Blumberg, M. In Applied Polymer Symposia, No.4, 175-188.
6. Fatal fall accident of the owner of a window washing business in Halifax, N.S. Personal communication.
7. Two independent incidents of failures of the used, 3/8" dia. polypropylene handlines during lifting of 25kV transformers. Personal communications.
8. “New Aspects in the Production of High-UV Stabilization Polypropylene Fibres”, Huttner, G., Supanz, P., Schneider H. in “Polypropylene Fibres and Textiles” (Conference Materials), Linz, Austria.
9. “Polysteel” Product Data Sheet. M.C.M. Ropes and Rigging, Vancouver and Toronto, October 1994.
10. “Fall Arrest Systems - Practical Essentials”, Sulowski, A.C., CSA International, Toronto, ON, 2000.
11. “Introduction to Fall Protection”, Second Edition, Ellis, J.N., ASSE, Des Plaines, IL, 1993.
12. ANSI Z359.1-1992 (R1999) American National Standard safety requirements for personal fall arrest systems, subsystems and components. American National Standards Institute Inc., New York, NY, and American Society of Safety Engineers, Des Plaines, IL.
13. “Qualified Inspector of Fall Protection Equipment” Seminar Manual, Sulowski Fall Protection Inc., Toronto, ON, 1997.
14. “The Fundamentals of Fall Protection” Seminar, CSA International, Toronto, ON, 1999.