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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 9. Respiratory Disease HHEs and Technical Assistance

9.1 Flockworkers Lung Disease

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HETA # 96-0093-2685 Microfibers Inc. Pawtucket, RI (A9-9)
HETA # 98-0238-2789 Spectro Coating Corp. Leominster, MA (A9-10)
HETA # 98-0212-2788 Claremont Fibers Corp. Claremont, NH (A9-11)
HETA # 2004-0013-2990 Hallmark Cards Inc. Lawrence, KA (A9-12)
HETA # 2004-0186-3011 Claremont Fibers Corp. Leominster, MA (A9-13)


An occupational medicine physician at Brown University in Rhode Island identified two interstitial lung disease cases in young workers. This prompted Microfibres Inc. to request a HETA to explore the unknown cause in 1996.


RDRP investigators conducted a cross-sectional study of the sentinel plant. The plant made carpet-like material for use in automobile upholstery. To make this material, the workforce cut long nylon strands into short nylon fibers called flock. The flock was then impacted onto adhesive-coated fabric to make a carpet-like product. Although the flock was not of respirable size, nylon fragments in the respirable size range were generated in the cutting and milling of the nylon flock. Evaluation of exposure-response relationships demonstrated associations between flock dust exposure and symptoms, diagnoses, and pulmonary function abnormalities. These associations supported attribution of a new interstitial lung disease to flock-associated dusts.

Animal studies stimulated by findings of the HETA investigation supported the biologic plausibility of respirable nylon flock causing lung pathology. The disease was subsequently shown to be pathologically-unique (lymphocytic bronchiolitis and peribronchiolitis), severe (with some cases requiring intensive care unit ventilation), slowly reversible over months to years, and present across the international flocking industry in relation to several synthetic polymers (nylon, rayon, polyethylene, and polypropylene).

Dissemination of HETA findings about this new lung disease risk resulted in 1998 management requests for investigation at two Massachusetts flock companies, each of which had a biopsy-confirmed case. This body of work also triggered a worker request for an evaluation at a Kansas greetings card-making plant using rayon flock to make soft, fuzzy greeting cards. A state health department request was also received to conduct follow up investigations at a previously evaluated flock plant after a new case was identified in 2005.

Outputs and Transfer

As detailed in chapter 3.3b, the five hazard evaluation investigations resulted in company-specific reports; presentations at four American Flock Association national meetings (in 1999, 2000, 2005, and 2006); stimulation of animal model work; a pathology workshop which described the unique pathology; presentations at the 6th International Conference on Environmental and Occupational Lung Disease (1999); and seven research publications (A9-14), one of which is cited here (1, A9-15)

Intermediate Outcomes

As noted above, initial HHEs raised awareness of this condition in the flock industry, leading to recognition of new cases and to other HHE requests. In addition, HHE results motivated engineering controls to be implemented at the sentinel Rhode Island plant, as well as at a Massachusetts and Kansas plant. The Rhode Island plant manager became an impassioned advocate for workplace safety, which resulted in his plant achieving lower injury claim rates at well below the textile industry average. The company consulted NIOSH in 2004 regarding a case of flock workers’ lung from their North Carolina flock plant, and NIOSH follow back with the physician raised concern for several alleged cases.

What’s Ahead

Flock companies have complied with some key RDRP recommendations for how to lower dust exposures. However, recommendations to eliminate use of compressed air to clean loose flock from plant equipment, a practice known to be associated with generation of extreme dust levels, have been less acceptable to the industry. Until improved control technology for the cleaning process proves feasible flock workers will remain at risk of disease.

In response to this problem, RDRP investigators successfully competed for intramural research funds to document whether shrouded devices using compressed air to clean equipment are feasible for use in the flock industry. This engineering control has the potential to lower exposures and reduce risk for flock workers’ lung. Unfortunately, much remains to be done to assure the elimination of this disease.