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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 3. Interstitial Lung Diseases > 3.3 Fiber-Induced Diseases

3.3b) Identification and Control of a Newly Recognized Occupational Lung Disease Affecting Flock Workers

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In 1996, an employer requested, through the HHE and Technical Assistance mechanism (chapter 9), that RDRP investigate the highly unusual occurrence of multiple cases of biopsy-documented interstitial lung disease among workers at a small textile plant in Rhode Island. The plant produces nylon flock and flock-coated upholstery fabric, and a university-based occupational medicine consultant had been unable to determine a cause for the disease, even after a walk-through assessment of the plant. RDRP investigators undertook the HHE at the plant to confirm the disease cluster (nine diagnosed cases from a plant with a workforce numbering about 150) and to identify an etiology with the intent of recommending measures to prevent the occurrence of additional cases.


While the university-based consultant (and colleagues) took the lead on describing the detailed clinical characteristics of the diagnosed cases, RDRP took the lead on investigating the possible occupational etiology of this disease cluster. Both parties cooperated on an initial effort to determine whether the interstitial lung disease incidence rate among workers at this plant exceeded that expected based on U.S. population rates.

To characterize airborne contaminants in the plant and to investigate associations between occupational factors and a respiratory symptom complex consistent with interstitial lung disease, RDRP field investigators conducted an initial assessment of the plant processes and exposures, including a walk-through survey and initial qualitative air sampling for various contaminants. We later did more comprehensive work area air sampling and a medical survey of current employees for epidemiological analysis. Our laboratory-based researchers analyzed the nature of the airborne dust collected from the plant and conducted animal studies to characterize the respiratory toxicity of this dust.

Throughout the investigations, our researchers held meetings with plant management, worker representatives, state authorities, the academic investigators engaged in complementary studies involving the diagnosed cases, and medical and industrial hygiene consultants hired by the plant. At the meetings our investigators presented preliminary findings and, through discussion with those present, learn additional details about the plant and its processes. That information guided subsequent investigation. In addition, through a CDC “Morbidity and Mortality Weekly Report” (MMWR) article, we requested that any physicians diagnosing interstitial lung disease in flock workers report them to NIOSH. To better document and understand what appeared to be a new occupational lung disease (dubbed “flock workers’ lung” by the university-based consultant), our investigators organized a multidisciplinary workshop to review a total of 20 diagnosed cases, including 15 biopsied cases from four different plants. The workshop involved experts from RDRP and the Ontario Ministry of Labour, the occupational medicine, pulmonary, and pathology specialists who diagnosed the cases, and several highly respected and knowledgeable pulmonary pathology consultants (from the Armed Forces Institute of Pathology, Duke University, and the Mayo Clinic). Clinical, industrial hygiene, epidemiological, and histopathological aspects of the cases where presented and discussed at the workshop. RDRP investigators went on to conduct additional HHEs at the other U.S. flock plants where cases considered at the workshop had been diagnosed. 

We found that sub-clinical disease among current workers at the Rhode Island flock plant was more widespread than previously realized, and that prevalence was significantly associated with time worked per week, working specifically with the flocking process, and using compressed air to clean-up loose flock between production runs. Similar, though less striking, findings were found at other investigated flock plants.

Our laboratory researchers found that fibers in the respirable size range comprised a substantial portion of the small airborne particulate and that these respirable fibers at the Rhode Island plant were nylon in composition. Our researchers further identified the likely source of the respirable fibers. The cutting of nylon tow filaments with high-speed rotary cutters, that are not optimally sharpened and aligned, causes melting and tailing of nylon at the ends of the cut flock. These small and elongated tails have a propensity to break off during subsequent mechanical milling of the flock. The employer, having focused on macroscopic (and non-respirable) flock as their product, had no prior awareness of the presence of this respirable particulate in the plant. Indeed, many process cyclones used to pneumatically convey flock within the plant had been openly exhausted into the workplace, unwittingly serving as generators of hazardous dust exposure for the workers. Our toxicologists found that dust from the Rhode Island plant caused intense inflammatory response in animal lungs compared to control exposures, as did laboratory-generated respirable nylon fibers similar to those observed in the plant air. On the basis of their findings, our investigators defined occupational exposures to flock-associated dust as a health hazard and specifically implicated respirable-size synthetic organic fibers as etiological. In their reports, our investigators emphasized recommendations to prevent the occurrence of further cases (e.g. reduction of worker exposures to airborne dust, including exhausting of process cyclones to the outside, limited use of compressed air for cleaning, and improved maintenance of cutters, together with implementation of a respirator program and a medical screening and surveillance program to identify any new cases that might arise despite implementation of the other recommendations).

Outputs and Transfer

An initial output, published in 1997, well before our investigations relating to the Rhode Island plant were complete, was a preliminary report in CDC’s “MMWR” (5, A3-101). Jointly reported by RDRP investigators and the university-based consultant (and colleagues) who initially evaluated the index cases, this report described the diagnosed cases of interstitial lung disease among workers at the Rhode Island plant and documented that the interstitial lung disease incidence rate among workers at this plant substantially and significantly exceeded that expected based on U.S. population rates. This led our investigators to continue to pursue its likely occupational etiology. The report was intended to rapidly notify public health authorities and clinicians of the unusual cluster of interstitial lung disease at the Rhode Island flock plant and to request that any additional cases of interstitial lung disease diagnosed in flock workers at any plant be reported to NIOSH to assist in assessing the extent of disease.

Following the HHE Reports on the Rhode Island plant,85 completed in 1998, four additional HHE Reports have been produced by RDRP investigators on other plants.86,87,88,89 Each report describes details of the investigations, findings, and preventive recommendations for specific plants.

RDRP investigators have to date published four peer-reviewed papers on the investigations pertaining to specific flock plants. One paper, published in the “Journal of Toxicology and Environmental Health” in 1999 describes conditions in the Rhode Island plant, including the noteworthy unexpected finding of the respirable nylon fibers in airborne dust samples from the plant (6, A3-102). Another paper, published in the same 1999 issue of the “Journal of Toxicology and Environmental Health” describes the pulmonary toxicity in an animal model of both nylon flock from the plant and laboratory-created nylon fiber with similar dimensional characteristics (7, A3-103). A third paper describes the epidemiologic findings from our survey of the Rhode Island plant, documenting the occurrence of sub-clinical occupational lung disease among the workers and its relationship to jobs involving exposures to flock-associated dust (8, A3-104). The fourth paper, published in a 2005 issue of the “American Journal of Industrial Medicine,” describes investigations and findings conducted by our investigators subsequent to the Rhode Island plant investigations, confirming the presence of dust-associated (and compressed air ‘blow-down’-associated) respiratory morbidity at these other flock plants. This documented that the disease was not limited to one plant or one company (9, A3-105). A fifth paper concerned with the implications of rayon flock-associated dust in occupational respiratory disease has been published recently (A3-105s).

Our investigators organized and hosted a workshop on “flock workers’ lung.”  The invited pathology consultants identified a distinctive lung tissue abnormality in cases from each of the four plants where diagnosed cases worked. This firmly established the condition as a newly recognized occupational lung disease. Two papers, both jointly authored by RDRP investigators and participating outside experts, were published to summarize findings of the workshop. The first of these reports, published in the “American Journal of Respiratory and Critical Care Medicine” in 1999, summarized the proceedings and conclusions of the workshop in a journal read by clinicians and scientists with respiratory disease interests (10, A3-106). The second, published in the “American Journal of Surgical Pathology” in the same year, served to provide a description of this newly recognized disease, including detailed histopathologic characteristics, to a readership dominated by practicing clinical pathologists (11, A3-107).

In addition, to help spread awareness of this newly recognized occupational lung disease and associated occupational respiratory hazard, RDRP investigators made scientific presentations at an international organic dust research conference, and at other regional, national, and international scientific meetings covering the gamut of toxicology, general occupational health, occupational and pulmonary medicine, and industrial hygiene disciplines.

RDRP investigators also hosted several meetings with representatives of the major domestic producer of nylon tow, the continuous nylon filament raw material used in flock processing, to inform them of this newly recognized hazard and discuss product stewardship issues.

To assure effective communication of this newly recognized disease and its etiology and prevention to non-scientists with a need to know, RDRP investigators held meetings with management and workers at each plant that was studied.

RDRP investigators also met on several occasions to discuss this newly identified hazard and disease with a flock engineering consultant who was widely used by flock companies and who also served as editor of the international trade journal, “Flock.” Our investigators also made several presentations to several annual meetings of the American Flock Association (the relevant trade association) and to an international trade association meeting on flock.

Intermediate Outcomes

As a result of the initial MMWR report jointly authored by RDRP investigators together with university-based consultants, additional cases of “flock workers’ lung” were recognized and reported from other flock plants operated by other companies, indicating that the risk for this disease extended well beyond the plant in Rhode Island and the company that operated this plant.

As a result of RDRP findings from investigations relating to the flock plant in Rhode Island, the management of that plant reported that it modified work processes and carried out a multi-million dollar upgrade of its ventilation systems to reduce worker dust exposures. It also established a respirator program and medical monitoring program to help protect workers engaged in the high risk job activities by facilitating early detection of affected employees. 

Other flock plants have reported similarly adopting plant-specific preventive measures based on plant-specific recommendations provided by RDRP reports and guidance disseminated by the industry trade association.

Based on RDRP publications and presentations to the national trade association, the American Flock Association established a new Occupational Health Committee that translated RDRP findings into a toxicity alert on the newly recognized hazard and how to prevent it. This was distributed to all American Flock Association member companies, effectively reaching the universe of flock plants in the U.S., with their estimated total of approximately 2500-3000 employees.

RDRP findings relating to “flock workers’ lung” also motivated the American Flock Association and at least one member company to undertake specialized scientific evaluations of factors associated with imprecise cutting of nylon tow that have provided the industry with refined guidance for minimizing the risk of generating undesirable respirable nylon fibers during flock production.

Motivated by RDRP presentations and targeted discussions, the editor of the international trade journal, Flock, wrote and published an editorial in the journal about the need for managers of flock companies to take action to prevent this newly recognized disease. In addition, an RDRP investigator make a plenary presentation at an international flock trade association meeting in 1999, summarizing what we had learned about the newly recognized disease and its cause and means of prevention. Flock published and disseminated an abstract of that presentation,90 as well as a full paper based on the presentation.91

Following the lead of RDRP investigators and collaborating investigators in the U.S.-based investigations, researchers in other countries have undertaken investigations of flock workers. These international efforts are evidenced in separate published studies documenting previously unrecognized occupational respiratory morbidity among polypropylene flock workers in Turkey and polyethylene flock workers in Spain.92,93

Progress Towards End Outcomes

While RDRP has no direct knowledge, reports from the company it initially investigated in Rhode Island indicate that no new cases from this plant have been reported since implementation of the exposure control modifications. Likewise, very few U.S. cases have been reported to us in recent years, suggesting that the occurrence of clinically recognized “flock workers’ lung” among U.S. flock workers may now be reduced. A remaining issue is the continuing use of compressed air to clean loose flock from plant equipment, a practice that is known to be associated with generation of extreme dust levels.

What’s Ahead

RDRP is currently engaged with four cooperating flock companies in an engineering control project to further prevent “flock workers’ lung” through reduction of exposures to respirable airborne flock-associated dust in flock plants. Cleaning settled flock from process equipment between production runs continues to represent a challenge for companies, which continue to rely extensively upon use of compressed air for that purpose, despite recommendations by our investigators to curtail its use. Our investigations at several plants have documented the extremely high levels of airborne particulate, including respirable particulate, generated during so-called “blow downs” and the association of disease with these “blow-downs.” The specific focus of the current ongoing project is to evaluate efficacy and acceptability of a prototype cleaning system that integrates compressed air into a vacuum system to assist in the capture of fugitive flock. Modifications to the prototype will be made as the need is identified. Results of the evaluation will be communicated to potential users primarily via presentations at the annual American Flock Association meeting and though dissemination of educational materials (e.g. “NIOSH Workplace Solutions”).

85. Washko R, Burkhart J, Piacitelli C [1996]. Health Hazard Evaluation Report HETA 96-0093-2685, Microfibres, Inc. Pawtucket, RI. 

86. Daroowalla F, Wang ML, Piacitelli C, Burkhart J, Jones W [1998]. Health Hazard Evaluation Report, HETA-98-0212-2788, Claremont Flock Corporation, Claremont, New Hampshire.

87. Daroowalla F, Wang ML, Piacitelli C, Burkhart J, Jones W [1998]. Health Hazard Evaluation Report, HETA-98-0238-2789, Spectro Coating Corporation, Leominster, Massachusetts.

88. Piacitelli C, Antao V [2004]. Health hazard evaluation report: HETA-2004-0013-2990, Hallmark Cards, Inc., Lawrence, Kansas.

89. Antao V, Piacitelli C [2004]. Health hazard evaluation report: HETA-2004-0186-3011, Claremont Flock Corporation, Leominster, Massachusetts.

90. Castellan RM [1998]. A newly recognized respiratory illness among workers at a flocking plant in the USA: Results of NIOSH investigations. Abstract. Flock 24:14.

91. Castellan RM, Burkhart J, Jones W, Porter DW, Eschenbacher WL [1999]. A newly recognized respiratory illness among workers at a flocking plant in the USA: Results of NIOSH investigations. Flock 99 (15th International Symposium Proceedings), 6:1-30.

92. Atis S, Tutluoglu B, Levent E, Ozturk C, Tunaci A, Sahin K, Saral A, Oktay I, Kanik A, Nemery B [2005]. The respiratory effects of occupational polypropylene flock exposure. Eur Respir J. 25:110-117.

93. Barroso E, Ibanez MD, Aranda FI [2002]. Romero S. Polyethylene flock-associated interstitial lung disease in a Spanish female. Eur Respir J. 20:1610-1612.

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