  The residence time of dust grains inside turbulent molecular clouds is
calculated. Earlier estimates of this time by Boland & de Jong (1982) have been
criticized by Prasad et al. (1987) for not taking into account properly the
turbulent character of the velocity field in molecular clouds which implies
that the trajectory of a dust grain should be treated as a random walk. Taking
some minimal assumptions regarding the turbulent velocity field a time scale is
derived that depends on the Reynolds number of the flow. The near
proportionality with Reynolds number of this time scale results in a much
longer time scale over which dust grains will remain inside a molecular cloud.
