These extensive and carefully controlled human exposure studies demonstrated that mild washing (essentially water rinsing) of cotton on a continuous batt or rayon rinse system has two major effects relevant to occupational respiratory disease prevention among cotton textile workers. First, mild washing physically removes dust from the cotton, generally reducing subsequent generation of respirable dust by about 50% (range, 35% to 67%). Second, mild washing markedly reduces the acute airway toxicity of residual dust, as measured by acute ventilatory responses of experimentally exposed human subjects. Both beneficial effects were shown to vary somewhat depending on specific washing methods used and on the initial potency of the cotton washed. Details have been published elsewhere [Wakelyn et al. 1986].
In contrast to mildly washed cotton from continuous batt and rayon rinse systems, mildly washed cotton from a batch kier washing system (though clearly much less potent than unwashed cotton dust) was found in some cases to retain significant acute airway activity in the human exposure studies, as measured by acute ventilatory responses [Castellan 1986]. The variable results observed were attributed to channeling of wash and rinse solutions through the cotton, which prevented thorough removal of dust and soluble material from the cotton fibers. Channeling was caused by hand loading directly from the bale without mechanical opening, cleaning, or prewetting.
Exemption from all requirements of the standard except for medical surveillance and medical recordkeeping is provided for higher grade cotton (low middling light spotted, or betteri.e., color grade code 52 or better and leaf grade code 5 or better according to the current classification system [USDA 1993a]) that is washed: (1) on a continuous batt system or rayon rinse system, (2) with water, (3) at a temperature of no less than 60°C, (4) with a water-to-fiber ratio of no less than 40:1, and (5) with bacterial levels in the wash water controlled to limit bacterial contamination of the cotton.
Lower grade cotton (i.e., below color grade code 52 or below leaf grade code 5 by the current classification system [USDA 1993a]) that is washed as specified in the preceding paragraph for higher grade washed cotton and is also bleached is exempted from all requirements of the standard except for medical surveillance, medical record- keeping, and a 500-µg/m3 PEL for airborne dust measured by the vertical elutriator sampler. With respect to washed cotton of mixed grades, the 1985 revised standard specifies that the requirements for the grade with the most stringent requirements would apply.
OSHA's Director of Policy anticipated the limitations of the 1985 revised standard in stating that "OSHA hopes to receive additional information as to acceptable cotton washing methods and alternative ways of predicting human respiratory response to cotton dust exposure" [Goldin 1984]. This, together with the projected availability of batch kier systems (in contrast to continuous batt or rayon rinse systems) for washing cotton, and along with improved technology for modern batch kier systems already in use for medical grade washing and stock dyeing of cotton, led to further evaluations of batch kier systems as a means of pretreating cotton to reduce toxicity.