A New Penetration Test Method: Protection Efficiency of Glove and Clothing Materials Against

Reported cases of allergic contact dermatitis caused by methylenediphenyl diisocyanate (MDI) have increased and thereby increased the need for adequate skin protection. Current standardized permeation and penetration test methods give information about efficacy of protective materials against individual components of the polyurethane systems. They do not give information of what kind of clothing materials workers should wear against splashes when handling mixed MDI-polyurethane formulations, which contain MDI, its oligomers, and polyols. The aim of this study was to develop and validate a sensitive penetration test method that can be used to select clothing that is protective enough against uncured splashes of MDI-polyurethane, still easy to use, and also, to find affordable glove materials that provide adequate protection during a short contact. The penetration of MDI through eight representative glove or clothing materials was studied with the developed test procedure. One MDI hardener and two polymeric MDI (PMDI)-polyol formulations representing different curing times were used as test substances. The materials tested included work clothing (woven) fabric, arm shields (nonwoven fabric), old T-shirt, winter gloves, and gloves of nitrile rubber, leather, vinyl (PVC), and natural rubber. A drop (50 μl) of test substance was added to the outer surface of the glove/clothing material, which had Tape Fixomull attached to the inner surface as a collection medium. After penetration times of 5 or 20 min, the collecting material was removed and immediately immersed into acetonitrile containing 1-(2-methoxyphenyl)-piperazine for derivatization. The formed urea derivatives of 2,4′-MDI and 4,4′-MDI were analysed using liquid chromatography with mass spectrometric and UV detection. The precision of the test method was good for the material with high penetration (work clothing fabric) of MDI, as the relative standard deviation (RSD) was 14 and 20%. For the arm shield with a low penetration (the nonwoven fabric), the precision was lower with RSDs of 35 and 50%. For two clothing materials, the penetration was high (134–577 μg cm−2). Low penetration (<0.5 μg cm−2) was shown by the arm shield and the natural rubber glove. Three glove materials showed no detectable MDI penetration (<0.002 μg cm−2). Two affordable glove materials (natural rubber and nitrile rubber) and one clothing material (dust proof arm shield) that can provide adequate protection during short contact with solvent free PMDI formulations were found. The new test procedure should be standardized in order to get a new international penetration standard. K e y w o r d s : clothing; gloves; isocyanates; MDI; penetration; protective materials; sensitizer; testing Ann. Occup. Hyg., 2015, Vol. 59, No. 2, 221–231 doi:10.1093/annhyg/meu078 Advance Access publication 16 October 2014 I n t r o d u c t I o n Isocyanates are respiratory and skin sensitizers and a well-known cause of occupational asthma. The awareness of health risks caused by inhalation exposure has resulted in more efficient protection against airborne isocyanates and thereby decreasing exposure to these harmful substances. Meanwhile, reported cases of allergic contact dermatitis have increased and especially for methylenediphenyl diisocyanate (MDI) after commercial MDI (polymeric MDI [PMDI]) and methylenedianiline (MDA) were included into the patch test battery (Goossens et al., 2002; Aalto-Korte et al., 2012; Engfeldt et al., 2012). Nowadays, according to the Finnish Register of Occupational Diseases (2008–2011), the annual mean number of diagnosed allergic contact dermatitis caused by MDI has reached the same level as for the reported asthma cases (3). Due to its low volatility, PMDI has become the dominant isocyanate produced and technically used word-wide. The skin of workers handling PMDI in gluing and foaming is often exposed to small splashes of formulations containing both MDI and polyols, without solvent dilution. Skin exposure caused by MDI penetration through gloves and clothing is also possible, but these hazards are not always recognized at workplaces. Permeation and penetration test methods do not give information of what kind of clothing the workers should wear against splashes of the glue and foam at work. The right type of glove for direct contact with PMDI and for washing the work equipment with solvents can be chosen based on work of the International Isocyanate Institute in 1993 and 1996 (American Chemistry Council, 2013). However, for most of the working time, starting with the mixing process, workers are mainly in contact with the mixture of PMDI and polyol, not with the MDI hardener as such. This contact time is for practical reasons very short, 10–20 min, due to the ongoing hardening process. PMDI-polyol formulations cannot be used as test chemicals using the existing permeation test or penetration methods since these components would react forming solid polyurethane which would destroy the testing equipment (EN ISO 6529, 2001; EN 374-3, 2003; EN ISO 6530, 2005; ASTM F 739, 2012). Due to lack of suitable test methods, there is no information available on what type of clothing or gloves the worker should wear against splashes of the glue or foam. The test results of MDI permeation bring about the need for leak-tight chemical protective suits (Forsberg and Mansdorf, 2007), which are burdensome and create physical stress. In addition, a new penetration method is needed since the existing penetration methods in use are based on weighing of the penetrated chemicals (EN ISO 6530, 2005). Weighing is not a selective method for the MDI component and is not sensitive enough for a chemical that is able to sensitize at low concentrations. Penetration is described as a movement of a chemical through porous materials, seams, pinholes, or other imperfections in a material. Permeation is a diffusion process in which the chemical first has to absorb into the intact material and also desorb out of the material (EN 374-1). Neither penetration nor permeation test methods can differentiate which process causes the movement of chemical through the material. The developed method was called a penetration method, because of the ability to test penetration through porous materials. The aim of this study was to develop and validate a penetration method that can be used to select clothing that is protective enough against splashes, still easy to use, and also, to find affordable glove materials that provide adequate protection during the short (5–20 min) contact with formulations of PMDI and polyol. The developed technique utilizing disposable equipment was used to measure the penetration of MDI from PMDI formulations of different curing times through eight representative glove or clothing materials. The test results are compared to results from permeation testing and to suggested safety limits for protective materials. M At e r I A l s A n d M e t h o d s Study design After choice of collection medium, the tape collection was validated and then the developed method was used to test the penetration of MDI though eight different materials. Test conditions during the different phases of development of the penetration test and during the testing are summarized in Table 1. Test formulations MDI hardeners (PMDI) are chemically a mixture of monomeric and oligomeric MDI. MDI or pure 222 • A new penetration test method