Some publications have been identified in the course of the project in which different test standards have been compared and evaluated.
All sets of standards available for determination of the breakthrough time described in section 3.1 allow the user to select their own collection medium. CHAO et al. (2010) have used the ASTM F739 in vitro test method in order to gather information about the influence of the collection medium on the result of a permeation measurement. The permeation of dimethyl formamide and methyl ethyl ketone through neoprene were tested with methanol, ethanol, 2-propanol and acetone as collection medium. Clear differences were found whereas solubility parameters could be used for interpretation purposes. Methanol was suggested as collection medium while ethanol, water, and 2-propanol showed a low capacity for the permeating DMF.
Results found by Mäkela et al. (2003) demonstrate differences between the test standards ASTM F739 and EN374, which were used to compare breakthrough times and flow rates for surgical gloves. While breakthrough times according to the ASTM are already reached, according to the EN standard the flow rate is not high enough yet (example: formaldehyde solution).
This can be explained by the different fluxes used for the definition of breakthrough (0.1 vs. 1 µg/cm2·min) (see also (DUPONT, 2012)). No method has been identified that can transform results of both techniques into each other. The authors consider it unlikely that such a method can be derived as the difference between both results depends on the substance and the slope of the permeation function.
While a long breakthrough time is usually considered to be good, a glove with a shorter breakthrough time according to a certain test standard can still show a better exposure reduction than one with a longer breakthrough time if the steady state permeation rate is lower (Figure 3.1). However, this is mainly relevant for gloves that are worn longer than the breakthrough time, which should not be the normal case as long as good occupational practice is in place.
Figure 3.1 Permeation rate as a function of time. Different definitions of the minimum breakthrough time.
Another aspect has been evaluated by PERKINS and POOL (1997) who have measured the permeation rate at steady state, the breakthrough detection time (ASTM F1407), the cumulative permeation at 125 minutes and the glass transition temperature (Tg) for two makes of nitrile gloves in four batches. Considerable variation was observed batch-to-batch variability was statistically significant for all parameters except the breakthrough detection time, suggesting that the same might apply to the resulting exposure.
MICKELSEN and HALL (1987) compared breakthrough times for identical glove types (concerning material and thickness) of different manufacturers. They found that breakthrough times varied considerably (max. factor 10 difference). However, it was recognised that only the breakthrough time was evaluated while also other parameters influence the final protection. Reasons for these differences may be as an example different raw materials / mixtures, vulcanisation methods or different fractions of (material) layers in the gloves.
Furthermore it is often emphasized that conditions in these tests do not necessarily meet those found in reality. As an example, OPPL summarises findings of other authors who report temperatures above the test temperatures and higher elongation especially in the finger area of gloves. An elongation of 50% in pre experiments resulted in a breakthrough time which was reduced about a factor of 2.3 Simulated hand movements (not permanent elongation) resulted in a reduction of the
3 Reference cited in OPPL 1999: Engler R, Heudorfer W: Prüfung der Chemikalienbeständigkeit von Schutzhandschuhen, Chemie in Labor und Biotechnik 48(1997)7, 286-291, sowie Engler R, Heudorfer W: Chemikalienbeständigkeit von Schutzhandschuhen, Sicherheit + Management (1997)3, 190-193;
Leicher JP: Chemikalienschutzhandschuhe (CSH), Arbeitssch.akt. (1996)3, 8-10.
breakthrough time of 20-40%, whereas interval elongation in a permeation cell resulted in a longer breakthrough time (50-100% times longer)4.
It is described that mixtures have partly shorter breakthrough times than the pure substance, resulting in other glove requirements5.
As a consequence, OPPL suggests a review of the permeation test standards including the usage of higher test temperatures (35°C) , a test at 20% elongation of the material, exposures close to reality and in general substances found in reality (OPPL, 1999, 2003).
The corresponding experiments lead to a reductions of the breakthrough time for the combinations nitrile/ ethanol (152 vs. 137 or 136 min. constant or changing elongation at 35°C), chloropren / iso-octane (155 vs. 118 or 143 min. constant or changing elongation at 35°C), PVC / iso-propanol (153 vs. 36 or 59 min. constant or changing elongation at 35°C) and latex / ethanol (different results depending on type of elongation (area or length-wise elongation) in the pre experiments. Several workplaces and corresponding glove recommendations are discussed and tested as well (OPPL, 1999).
EVANS et al. found increased permeation rates and decreased breakthrough times with higher temperature ( body temperature). The difference between inside and outside of the glove caused by the body heat also may have a negative influence (butyl gloves, acetone and ethyl acetate as solvent). Butyl gloves were found to be impermeable to both solvents. For nitrile gloves and acetone a statistically significant influence was found, indicating increased permeation rates for a temperature difference (23/23°C vs. 23/35°C; 484 µg/cm2·min vs. 591 µg/cm2·min.) and increased overall temperature (23/23°C vs. 35/35°C; 484 µg/cm2·min vs. 657 µg/cm2·min.).
Breakthrough times decreased (23/23°C vs. 23/35°C; 8.6 vs. 7.4 min.; 23/23°C vs.
35/35°C; 8.6 vs. 6.3 min.). The same tendency was reported for nitrile gloves and ethyl acetate (permeation rates of 91, 101, 125 µg/cm2·min; breakthrough times of 22.9, 22, 13.7 min.). However, differences were reported to be not statistically significant (EVANS et al., 2001).
All mentioned aspects can significantly influence the measured breakthrough time, however, the most recent standards still recommend test temperatures of 23°C (NORMENAUSSCHUSS PERSÖNLICHE SCHUTZAUSRÜSTUNG (NPS) IM DIN DEUTSCHES INSTITUT FÜR NORMUNG E. V., 2015a, 2015b).
As a conclusion it can be said that although terms such as breakthrough time or the categorisation of PPE may seem straightforward, it should be kept in mind that differences may exist depending on the used standard and this can also influence the final exposure reduction. Exposure reduction measurements are occasionally required (e.g. gutter test, inward leakage test), however, often tests are not aimed at an estimation of efficiency values but of a concentration in µg / cm2 or visual examinations.
User variables such as behaviour cannot be reflected by in-vitro tests and only to a limited extent by other tests such as the spray test (EN ISO 17491-4).
4 Reference cited in OPPL 1999: Perkins JL, Rainey KC: The Effect of Glove Flexure on Permeation Parameters, Appl.Occup.Environ. Hyg. 12(1997)12, 206-210
5 Reference cited in OPPL 1999: Rheker R: Schutzhandschuhe beim Umgang mit Gefahrstoffen, Sicherheitsing. (1998)3, 28-32; Packham CL, Spoors R, Rowell FJ: Performance of chemical protective gloves under actual working conditions: a preliminary study (to be published (according to OPPL)