The surface of glass quickly develops very small micro cracks when exposed to high humidity. Although micro cracks can be safely ignored in most applications, they can significantly decrease the mechanical strength of very small glass structures such as optical fibers. Consider a glass optical fiber of diameter D_i = 125 pm that is coated with an acrylate polymer to form a coated fiber of outer diameter D_o = 250 Mm. A telecommunications engineer insists that the optical fiber be stored in a low-humidity environment prior to installation so that it is sufficiently strong to withstand rough treatment by technicians in the field. If installation of a roll of fiber requires several hot and humid days to complete, will careful storage beforehand prevent micro-cracking? The mass diffusivity of water vapor in the acrylate is D_AB = 5.5 x 10^-13 m²/s while the glass can be considered impermeable.