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EN ISO 374-4:2019 degradation testing of gloves
A mandatory requirement for degradation testing of chemical-resistant gloves is included in EN ISO 374-1:2016+A1:2018.
To assess whether a glove material is resistant to permeation by chemicals, testing is carried out in accordance with EN 16523-1:2015+A1:2018 against the specific challenge chemicals of interest. The performance levels achieved dictate the chemical protective glove type, as defined by the glove performance requirements standard EN ISO 374-1:2016+A1:2018. However, if a glove material achieves a high performance level for permeation resistance, it does not necessarily equate to a glove that will protect against chemicals, as the effect of degradation due to the chemical also needs to be considered.
What is degradation?
Degradation is defined as a deleterious change in one or more properties of a material due to contact with a chemical. Examples include flaking, swelling, disintegration, embrittlement, discolouration, a change in appearance, hardening or softening. In theory, a material could have an excellent resistance to chemical permeation, but as the EN 16523-1 test method to assess permeation requires the material to be motionless during the testing, it may perform poorly in 'real-life' situations if exposure to the chemical degrades the material. Degradation is not assessed to performance requirements as part of any permeation testing procedure, but observations on the appearance of the material after testing are included in test reports.
If a glove material were to harden or become brittle when exposed to a chemical in use, the dextrous nature of the glove would be compromised, and so would the protection this glove would provide to the wearer. For this reason, the European technical committee responsible for preparing glove standards (CEN TC 162 WG 8) developed a procedure that quantifies a change to a physical property after exposure to a challenge chemical. In 2019, this procedure was also adopted by ISO (the International Organisation for Standardisation) TC 94 SC 13. Rather than base the degradation test exposure time on the permeation performance level, a standard duration is selected for all chemicals. This exposure time against the challenge chemical is 60 minutes. Therefore, some chemicals that only just achieve a 'Level 2' permeation resistance (greater than 30 minutes) may have a very high degradation value.
The principle of this testing is to measure if there is a change in the force required to puncture the glove material after continuous contact of its external surface with a challenge chemical. This puncture test is very similar to the procedure detailed in the performance standard to assess protection from mechanical risks detailed in EN 388:2016+A1:2018. The force required to push a standard stylus through a sample of the glove material is compared before and after exposure to the challenge chemical.
Although EN ISO 374-1 contains no performance requirements, for chemicals referenced in the glove marking (code letters A, J, K, L, N and T in figure 1), the EN ISO 374-4 result must be included in the user instructions to make this information available to the end user. The test result is reported as a percentage degradation, so values could be positive (if the material has become weaker after chemical exposure) or negative (if the material has become harder after chemical exposure). Future revisions of EN ISO 374-1 may specify performance requirements, which could be a minimum change in puncture resistance after exposure to chemicals. However, this will only be considered once substantial data has been obtained on how different glove types perform to the conditions of this test.
The terminology and performance requirements for protective gloves against chemical risks are specified in EN ISO 374-1. There are requirements for permeation, penetration and degradation, in addition to the general requirements from EN ISO 21420:2020. An example of the pictogram for ‘type A’ gloves is shown in figure 1. For type A gloves, the permeation performance must be at least level two against a minimum of six of the chemicals listed in EN ISO 374-1:2016+A1:2018 table 2. The letters beneath the shield represent the challenge chemicals that achieved at least performance level 2 – in the example given here, these represent methanol (A), n-heptane (J), 40 per cent sodium hydroxide (K), 96 per cent sulphuric acid (L), 99 per cent acetic acid (N) and 37 per cent formaldehyde (T).
Testing at SATRA
SATRA has invested in specialist equipment in order to test in accordance with EN ISO 374-4 against a wide variety of challenge chemicals. Due to their hazardous nature, these challenge chemicals need to be handled in contained areas with local exhaust ventilation systems to control the risks for the analysts carrying out the testing. Temperature is also an important factor when assessing degradation, so all testing is required to be carried out at 23°C and 50 per cent relative humidity after conditioning in that atmosphere.
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