Respiratory Diseases And Their Prevention: A Look At Industrial Dust And Its Control
By Michael D. Shaw
"Dust" is a term loosely applied to solid particles predominantly larger than colloidal, and capable of temporary suspension in air or other gases. Derivation from larger masses through the application of physical force is usually implied. (Definition taken from Bertram D. Dinman, MD's article "The Mode of Entry and Action of Toxic Materials" from Patty's Industrial Hygiene and Toxicology.)
"Industrial dust," then, remains a rather nebulous concept for the very reason that the term itself encompasses a diverse array of specific dust subtypes arising as byproducts in various industries, most notably mining, construction/demolition, and refining/manufacturing/processing. These specific dust subtypes in turn give rise to the onset of respiratory diseases that have claimed their share of deaths (in the tens of thousands) during the previous decade (1990-1999).
Many workers are unaware of the potential hazards posed by industrial dust present in their work environment, ultimately placing them at higher risk for developing respiratory complications. In order to better understand industrial dust and its control, this article will be subdivided into (i) an overview of prevalent respiratory diseases associated with prolonged dust exposure and their major industrial sources (ii) NIOSH recommended preventive measures taken to rectify or mitigate such potential exposure.
Respiratory diseases resulting from industrial dust exposure
At least 1.7 million U.S. workers are exposed to respirable crystalline silica in a variety of industries, most prevalent of these being construction, mining, and primary metal operations.
Silicosis is a diffuse pulmonary fibrotic disease that ensues from an extensive and prolonged exposure to free crystalline silica dust. Inhalation of dust containing crystalline silica (alpha-quartz or silicon dioxide) or its polymorphs (tridymite or cristobalite) is the primary etiologic agent of this preventable yet irreversible disease. Workers exposed to silica dust are often exposed to asbestos as well, and many will develop asbestos-related respiratory diseases.
Silicosis treatment is extremely limited considering a lack of cure for the disease. However, like all occupational respiratory ailments, it is 100% preventable if exposure is minimized.
Coal Workers' Pneumoconiosis
Inhalation of coal dust for continued and prolonged time periods results in coal workers’ pneumoconiosis, also referred to as black lung disease. Apart from asbestosis, black lung disease is the most frequently occurring type of pneumoconiosis . In terms of disease pathogenesis, a time delay of nearly a decade or more occurs between exposure and disease onset. Not surprisingly then, most diagnosed individuals and deaths from this type of pneumoconiosis reflect working conditions of the past. According to the NIOSH Work-Related Lung Disease (WoRLD) Surveillance Report 2002, between 1990-1999, 15,036 deaths were attributed to respirable coal mine dust. As determined by frequency of industry listing on death certificates, the three major industrial sources of coal dust exposure are (in order of prevalence) coal mining; construction; and blast furnaces, steel works, rolling and finishing mills.
Asbestosis results when asbestos particles are inhaled into the lungs by exposed individuals in large quantities. Pathogenesis of the disease is characterized as progressive and irreversible, leading to subsequent respiratory disability. In severe cases, asbestosis results in death from pulmonary hypertension and cardiac failure. A unique aspect of asbestosis distinguishing it from other diffuse pulmonary fibrotic diseases (such as silicosis), is the presence of asbestos bodies and fibers in the lung tissue.
During 1990-1999, 10,914 deaths were attributed to asbestosis. The three major industrial sources of asbestos exposure as determined by frequency of industry listing on death certificates are (in the order of prevalence) construction; ship/boat building and repair; and chemical manufacturing industries.
Inhalation of asbestos particles is not only responsible for the onset of asbestosis, but in many instances may also cause the extremely progressive and fatal asbestos-linked cancer, malignant mesothelioma.
Mesothelioma is a rare form of cancer that affects the mesothelium, a protective cellular layer that encapsulates most internal organs of the body. Mesothelioma primarily targets the pulmonary mesothelium, specifically the pleura, but in certain limited cases, the mesothelium of cardiac and abdominal cavities have been susceptible as well. In the majority of cases, etiology is linked to inhalation of asbestos particles. Mortality within two years following diagnosis is nearly 100%. In 1999, 5070 lives were claimed from this almost entirely preventable disease.
Although malignant mesothelioma claims more lives each year than all other industrial dust induced respiratory diseases combined, its frequency in specific industrial workplaces is far less pronounced than other occupational lung diseases, as it appears to be more endemic to all sectors of employment.
Thus far we have considered industrial dust induced respiratory diseases that often prove to be fatal following diagnosis. There are also pulmonary complications caused by industrial dust exposure that although not fatal, induce acute to chronic respiratory symptoms. Of the numerous ailments, the most common of them, byssinosis and extrinsic allergic alveolitis, will be briefly considered.
Byssinosis, also referred to as brown lung disease, is an occupational respiratory disorder characterized by the narrowing of pulmonary airways. In the United States and Great Britain, byssinosis is usually caused by the inhalation of unprocessed cotton dust. Textile workers opening bales of raw cotton are at high risk of developing byssinosis. However, dusts from other vegetable fibers such as flax and hemp are also considered to be etiologic agents.
Symptoms of byssinosis include, but may not be limited to, wheezing and tightness in the chest as well as a prolonged cough. Symptoms are usually worse at the beginning of the work week and improve away from the work environment.
As would be expected, industries associated with the processing of cotton, specifically yarn, thread and fabric mills are most associated with worker exposure to cotton dust.
Hypersensitivity pneumonitis (HP), also commonly referred to as extrinsic allergic alveolitis or farmer's lung, is characterized by inflammation of the lungs. HP typically arises from exposure to organic dusts and leads to acute symptomology similar to byssinosis. If prolonged exposure persists, chronic lung disease may develop. Agricultural production involving livestock and crops is the major source of such exposure.
The most successful tool of prevention of respiratory diseases from industrial dust is to minimize exposure. However, this is not a practical approach from the perspective of industries such as mining, construction/demolition, refining/manufacturing/processing, where industrial dust is an unavoidable byproduct. In such cases, industries must implement a stringent safety protocol that effectively curtails exposure to potentially hazardous dust sources.
NIOSH has published lists of recommended precautionary measures to reduce exposure to a variety of industrial dust types. Although these lists are specific to each dust type, the principles of industrial dust control remain consistent. Below is a NIOSH list of recommendations for minimizing exposure to free crystalline silica dust.
Implementation of such measures serves as a prophylactic measure for risk of silicosis. Despite the bias of these measures for silica exposure, this list illustrates fundamental industrial dust control principles. As the majority of recommendations are generic, they may be implemented by most industries irrespective of specific dust byproducts to minimize airborne circulation and exposure.
NIOSH recommends that respirators should not be used as the primary means of preventing or minimizing exposures to airborne contaminants. Instead, use of effective dust source controls such as substitution, automation, enclosed systems, local exhaust ventilation, wet methods, and good work practices should serve as the primary means to protect workers. Use of respirators should only occur when dust source controls cannot maintain exposure below the NIOSH recommended levels. In these cases, source controls should be supplemented with the use of respirators.
Despite the potentially fatal respiratory diseases that ensue from prolonged exposure to various industrial dust subtypes, with proper preventive strategies, industries can virtually eliminate health risks to their workers. Recognition of industrial dust subtypes as etiologic agents and implementing measures to minimize exposure prove most important in establishing a safe working environment. Initial trends in this decade suggest industrial dust related deaths are on the decline, presumably on account of implementing more successful cautionary measures. Indeed, new diagnoses of coal workers’ pneumoconiosis, has dropped from 25.3 per 10,000 full-time workers in 1998 to 10.4 in 2000.
Perhaps we have finally turned the corner on one of the most ancient foes of the worker—industrial dust.