Harmful substances for ropes and slings

What is new? Table 2 for classifying the hazardousness of substances for textile PPE has been updated and expanded.

During storage, transport and use personal protective equipment (PPE) for fall arrest may come into contact with chemical substances. While being transported, for example, in a car PPE may come into close proximity with engine oil, spare batteries or AdBlue. When used in industrial climbing, contact with chemical substances is also an issue, for example when cleaning special equipment or facilities or when handling motorized tools while climbing trees. Plastics are particularly affected by damage, as they are far more susceptible to chemical effects than metals. We want to address the question of how chemicals affect textile PPE and which substances are to be regarded as particularly critical.

CHEMICAL DAMAGE TO TEXTILE PPE

Background

On principle, there are two different effects of chemicals on textiles:

Chemical effect: the chemical reacts with the plastic and causes a decomposition reaction or a change in the molecular structure. The molecules of the chemical diffuse into the individual units of the polymer chain and weaken or break down its bonds. If there is a chemical reaction between the plastic and the medium, even small quantities can lead to pronounced changes in its mechanical properties.
Physical effect: if a medium does not react chemically with the plastic, it can still lead to a physical change in its properties. For example, this can result in surface changes and thus in the friction values, causing stiffening of the textile or swelling of the contaminated area. The changes resulting from a physical effect of the medium are reversible and can usually be remedied by washing out the chemical.

The three main materials used in textile PPE are polyamide (PA), polyester, more precisely polyethylene terephthalate (PET) and ultra-high-molecular-weight polyethylene (HMPE), also known under the trade name Dyneema. Substances which cause changes to the properties of plastics can be divided into acids, bases, solvents, salts and oxidizing agents. By determining the pH value of the chemical, an initial rough indication of possible damage can be obtained. A substance with a pH value of 7, which corresponds to that of water, is considered neutral. The lower the pH value, the more acidic the substance is. The higher the pH value, the more alkaline the substance is. In Table 1, the pH limits show the range at which an acid or base can have a damaging effect on the plastic.

The table shows that strong acids and bases have a damaging effect, especially on polyamide.

In general, there is a lot of information about the resistance of certain plastics to certain chemicals. Our motivation for publishing our own test series is to publish results on the contact of textile PPEgA with practically relevant substances, as the effect of mixed substances is not well researched. The aim is to sensitise PPE users as to which practically relevant substances are critical and therefore require special attention.

Method: How Were the Tests Performed?

Not all contamination is the same. The influence of chemicals on textile PPE depends on many factors. On the one hand, the chemical effect depends on the textile itself. In other words, on the exact material composition and construction of the textile. Secondly, the effect of the chemical is influenced by the external conditions, such as the type of contamination, the temperature or the exposure time. For our test, we have defined a worst-case scenario to analyse the effect on textile PPEgA. The exact test parameters are listed below:

Type of contamination: In practice, there are many ways in which the chemical can come into contact with PPE. From wetting by vapour to soaking the material in the substance, anything can happen and the intensity of the contamination varies accordingly. We contaminate the samples in an immersion bath to ensure diffusion of the chemical into the inner textile structures.
Exposure and reaction time: the exposure time describes the time period during which the textile is in direct contact with the chemical. We set a duration of at least 24 hours. The reaction time determines how long the chemical has time to dry and react with the material after direct contamination. We allowed a period of at least 24 hours in the climatic chamber.
Contamination and drying temperature: the temperature is a crucial factor for the reactivity of many chemicals, as an elevated temperature makes the molecular structures more mobile. This has a significant effect on the diffusibility of the chemical into the material, which is why the chemical resistance of plastics only applies to the specified temperature range. We chose to perform the contamination and drying at room temperature, i.e. 23°C (± 2°C) and a humidity of 50%, which corresponds to standard conditioning.
After the exposure and action cycle with the substance, the maximum tensile force of the samples was determined in a tensile test in accordance with EN 565 and compared with the initial values. The samples were also analysed for changes in physical properties.

The Results of the Contamination Tests

The results in Table 2 relate to the chemical resistance of the textile materials to the various substances at room temperature. Depending on the loss of strength, the hazardousness of the substance is divided into three categories:

Green, resistant: No reduction in the strength of the textile was found after the contamination test.
Orange, limited resistance: The textile loses strength slightly (less than 10 %) due to the contamination. After a longer exposure time (> 24 h), a significant loss of strength is to be expected.
Red, unstable: The textile loses its strength after a short time. A strong attack takes place, which leads to the complete destruction of the textile with very low tensile strength.

Observations of changes in physical properties are described in a separate column.

Table 2: Categorisation of the hazards of certain PPE textile products

Key: - No recognisable effect | *Value was not noted | **Because of the PA component | ***Exposure time 10 seconds!

Note: The table is a list of substances to be assessed as particularly critical and does not represent the release of substances assessed as green or orange.

We are endeavoring to expand this table to provide an overview of other substances and their chemical effects on textile PPE. However, caution is required when classifying the effects of substances:

the physical effect of chemicals can also have a major impact on their durability, as in the case of contamination of a kernmantle design. A stiffening of the sheath can be caused if the chemical penetrates into the sheath braid without penetrating into the core. Under mechanical load this stiffening can lead to a displacement of the sheath or to premature breakage of the sheath when falling over an edge.
Dyneema slings include some polyamide, which allows the textile composite to fail without the Dyneema deteriorating. The Dyneema threads are torn from the composite and thus can no longer sustain their maximum tensile strength. Therefore, even in the event of contamination with a chemical that is harmless to UHMWPE, caution is required and PPE should be discarded as a precaution.

Conclusion

The effect of chemical substances on PPE is complex and not easy to assess. Therefore, contact between PPE and chemical substances should generally be avoided.

Even though some chemicals are only harmful for certain materials, PPE should be discarded in the event of contamination with strong acids and bases, e.g. hydrochloric acid, grip or pipe cleaners—regardless of the textiles involved.

Moreover, this list is only exemplary and when classifying other substances it is essential to take into account that the components and concentrations of mixtures of substances cannot always be determined.

Bibliography

Koller, S.: Säureeinfluss auf Textilmaterial im Bergsport und deren Nachweisbarkeit, degree dissertation.