Washed Cotton in The 1978 OSHA Cotton Dust Standard

Current Intelligence Bulletin 56

Conclusions

A substantial body of experimental evidence now exists to indicate that, with respect to removal of potential respiratory toxicity, cotton mildly washed in batch kier systems (using modern equipment that assures thorough wetting of the cotton fiber and no reuse of wash or rinse water) is equivalent to cotton mildly washed on a continuous batt system in a manner acceptable to OSHA under the washed cotton provisions of the current cotton dust standard. Specifically, mildly washing cotton in modern batch kier systems using two different systems on two different occasions and using two different "worst-case" cottons resulted in consistent and effective removal of dust from cotton and reduction of endotoxin content of residual dust. Furthermore, as assayed by the NIOSH laboratory, the concentration of endotoxin in airborne dust from each "worst-case" cotton that had been mildly washed on each modern batch kier system was less than 12 ng of endotoxin per mg of dust, indicating that exposures up to a dust concentration (measured by vertical elutriator) of 0.75 mg/m3 would not exceed the "relative" threshold for an acute toxic effect on the airways described by NIOSH investigators [Castellan et al. 1987].

On the basis of these observations and the results of controlled exposures of human volunteers, the Task Force concludes that mild washing of cotton in modern batch kier systems will prevent the acute respiratory effects of occupational exposure to cotton dust. Because results of epidemiological observations of cotton textile mill workers have indicated a significant association between acute and chronic effects (see Appendix), the Task Force further concludes that mild washing of cotton in modern batch kier systems can also be expected to prevent the chronic effects of occupational exposure to cotton dust.

Recommendations

The Task Force for Byssinosis Prevention recommends the following:

1. OSHA should add mild washing in a modern batch kier system as an acceptable method to wash cotton under the 1985 cotton dust standard. Specifically, the pertinent part of the cotton dust standard [29 CFR1910.1043(n)] should be amended through the following additions in boldface type:

   (n) Washed Cotton—
   . . . . . . .
   (4) Higher grade washed cotton. The handling and processing of cotton classed as "low middling light spotted or better" (color grade code 52 or better and leaf grade code 5 or better according to the current USDA classification system begun in 1993) which has been washed:
   (A) On a continuous batt system or a rayon rinse system
   (i) With water,
   (ii) At a temperature of no less than 60°C,
   (iii) With a water-to-fiber ratio of no less than 40:1, and
   (iv) With bacterial levels in the wash water controlled to limit bacterial contamination of the cotton.

   (B) On a batch kier washing system*
   (i) With water,
   (ii) With cotton fiber mechanically opened and thoroughly prewet before forming the cake,
   (iii) For low-temperature process, at a temperature of no less than 60o C with a water-to-fiber ratio of no less than 40:1; or, for high-temperature process at a temperature of no less than 93o C with a water-to-fiber ratio of no less than 15:1, and
   (iv) With a minimum of one wash cycle followed by two rinse cycles for each batch, using fresh water in each cycle.

2. Where feasible, users of raw cotton should consider washed cotton substitution, either complete or in part (as a blend), as an adjunct means to achieve compliance with the current OSHA PEL for cotton dust when other engineering controls have not been entirely effective. In addition, even if compliance with the OSHA PEL has been achieved, washed cotton substitution should be considered as a means to further reduce potential risk of occupational respiratory disorders among workers exposed to cotton dust.
3. Research should be conducted to optimize textile processing of mildly washed cotton and, as commercial experience is gained, information should be disseminated regarding applications in which washed cotton can be feasibly substituted for unwashed cotton. Dissemination of this information may serve to promote voluntary substitution of mildly washed cotton for unwashed cotton by cotton-consuming companies as a prevention strategy.

*The purpose of this recommended revision is to encourage voluntary substitution of washed cotton for unwashed cotton as a strategy to prevent respiratory disorders induced by cotton dust.

Abbreviations