Chapter 22 Materials Selection and Design Considerations

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22.14 Assessment of CPC Glove Materials to Protect Against Exposure to Methylene Chloride • W117 Table 22.5 Characteristics and Costs for Commercially Available Chemical Protective Glove Materials That May Be Used With Methylene Chloride Diffusion Glove Breakthrough Surface Exposure Coefficient, D Thickness, / Time, tb Concentration, SA Rate, re Cost Material (10 �8 cm 2 /s) (cm) (min) (g/cm 3 ) (g/h) (US$/pair) Multilayer a 0.0095 0.007 1430 11.1 0.43 4.19 Poly(vinyl alcohol) 4.46 0.075 350 0.68 1.15 24.00 Viton rubber 3.0 0.025 58 0.10 0.35 72.00 Butyl rubber 110 0.090 20 0.44 15.5 58.00 Neoprene rubber 92 0.075 17 3.53 125 3.35 Poly(vinyl chloride) 176 0.070 8 1.59 115 3.21 Nitrile rubber 157 0.040 2.8 2.68 303 1.56 a Silver Shield TM Sources: Manufactures’ data sheets.
W118 • Chapter 22 / Materials Selection and Design Considerations Computation of exposure rate of a hazardous chemical that is diffusing through a chemical protective glove material C A C B substitutions for sion for re: and into Equation 22.28, we obtain the following expres- r e � DAS A / (22.29) Table 22.5 also includes, for these several glove materials, values of that were determined using Equation 22.29. At this point, a key question is: What is an acceptable and safe exposure rate? Based on airborne exposure limits set by the Occupational Safety and Health Administration (OSHA) of the US, the maximum allowable to methylene chloride is approximately 1 g/h. Now let us examine and compare computed breakthrough times and exposure rates for the several glove materials, as listed in Table 22.5. First of all, with regard to exposure rate, two of the seven materials meet or exceed the standard set by OSHA (viz., 1 g/h)—viz. multilayer (Silver Shield TM ) and Viton TM re rubber (with re values of 0.43 and 0.35 g/h, respectively). Relative to breakthrough time, the multilayer material has the longer tb (24 h versus about 1 h for the Viton rubber). Furthermore, the multilayer gloves are considerably less inexpensive (at $US4.19 per pair compared to $US72.00 for Viton rubber, Table 22.5). Therefore, of these two glove materials, other relevant characteristics/properties being equal, the one of choice for this application is multilayer Silver Shield. It has a significantly longer breakthrough time and is much less costly than the Viton rubber material, whereas there is very little difference between their exposure rates. The photograph of Figure 22.27 shows a pair of Silver Shield gloves. It should be noted that calculated breakthrough time values presented in Table 22.5 assumed the glove material had no previous exposure to methylene chloride. For a second application, some of the methylene chloride that dissolved in the glove during the first exposure probably remains; thus, the breakthrough time will be much shorter than predicted for an unused glove. For this reason, CPC gloves are often discarded after one usage. One final comment is in order: one should always consult an industrial hygiene specialist when selecting chemical protection clothing. These specialists are experts as to what materials are suitable for exposure to specific toxic chemical substances, Figure 22.27 Photograph of Silver Shield multilayer chemical protective gloves. (Photograph courtesy of North Safety Products, Anjou, Quebec, Canada.) r e
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Chapter 22 Materials Selection and Design Considerations

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