A downdraft table is a dust control device that reduces airborne wood dust during woodworking operations.
Hazard Analysis — Construction dust
Workers who cut boards and panels may be exposed to construction dust.
Cutting boards and panels to required size can generate construction dust which can cause chronic bronchitis and emphysema. Wood dust is another type of construction dust that can cause irritations or allergic reactions to the skin, respiratory tract and eyes. Exposure to some wood dust has also been linked to respiratory ailments such as occupational asthma and shown to be associated with nasal cancer.
Chronic obstructive pulmonary disease (COPD) includes chronic bronchitis and emphysema. Chronic bronchitis is present when someone has a regular cough with phlegm for at least 3 months per year for two years. Emphysema is present when there is destruction of the walls of the airspaces of the lung. The destruction of airspaces means there is less lung surface; loss of lung surface reduces the ability of the lung to transfer oxygen into the blood stream.
In 1999 COPD ranked as the fourth leading cause of death with over 124,000 deaths, and was a primary or contributing cause of death for an estimated 8.5% of the U.S. population. An estimated 16 million individuals in the U.S. had a diagnosis of COPD in 1994. Worldwide, COPD is projected to be the third leading cause of death by 2020. Eighty to ninety percent of COPD is caused, at least in part, by tobacco smoking, but exposure to dust is an important risk factor as well. The American Thoracic Society concluded that 15% of COPD was caused by occupational exposures, and that occupational dust and fume exposures can cause clinical bronchitis and loss of lung function in both smokers and nonsmokers. Dust may contain specific contaminants such as crystalline silica or hexavalent Chromium.
Smoking is the primary cause of COPD, but smoking alone does not explain all COPD, as only 15-20% of smokers developed COPD and 10% of deaths from COPD occur in persons who never smoked. Occupational exposures to dusts and chemicals (vapors, irritants, fumes) also cause COPD; the specific exposures in construction linked to COPD are wood dusts, cadmium, silica, welding fumes, cement dust, asbestos, and possibly isocyanates. For someone with heavy dust exposure over many years, the dust contributes as much to COPD as smoking does. Across all occupations, about 15% of COPD is caused by occupational exposures.
One study, “A case-control study of airways obstruction among construction workers”, examined occupational exposures to vapors, gases, dusts and fumes (VGDF) among older construction workers between 1997 and 2013, comparing 834 workers with COPD and 1,243 controls. Approximately 18% (95% CI=2-24%) of COPD in this population can be attributed to workplace exposures associated with construction tasks. After adjusting for smoking habits in this population, the study also revealed among construction workers who never smoked, 32% (95% CI=6-42%) of COPD was attributable to the workplace.
Airflow in nonsmokers without respiratory disease declines by 25 to 30 ml per year beginning at about age 35. The rate of decline of airflow is faster for smokers than for nonsmokers, and faster for those exposed to lots of dust. Individuals with COPD have more frequent chest illnesses, which also decrease lung function for several months.
When wood dust comes into contact with the skin, its non-allergic effect is usually irritation, which can lead to rashes or irritant dermatitis that tends to appear on the scalp, eyelids, neck, forearms, the backs of hands and genitals. These symptoms usually take approximately 15 days to develop and will only persist as long as the affected skin site remains in contact with the source of the wood dust.
Wood dust can also cause allergic contact dermatitis which is another form of dermatitis caused by sensitizers of certain wood dust species. This type of allergic reaction can produce the same effects as the non-allergic reaction to wood dust. The difference is that once the body is sensitized, it will set up an allergic reaction that can enable the skin to react more severely to even a small amount of that particular wood dust (or related wood species) in subsequent episodes of exposures.
Exposures to wood dust can affect the respiratory tract, such as the nose. Inhalation of wood dust can cause runny nose (rhinitis), sneezing, stuffed nose and nose bleeds. These symptoms usually arise from irritation, but can also be a consequence of allergic sensitation (i.e. rhinitis). Several studies have suggested that certain wood dusts, especially oak and beech (confirmed human carcinogens), but perhaps also birch, mahogany, teak, walnut (suspected human carcinogens) may cause nasal cancer, although rare.
Inhalation of wood dust can lead to obstructive patterns of respiratory changes, which can limit breathing flow rates and impair lung function. One lung condition attributable to wood dust exposure (especially Western Red Cedar) is occupational asthma, which includes wheezing, coughing, tightness across the chest and shortness of breath. Some wood dust can also cause asthma as an allergic reaction once the body is sensitized to that wood species.
Wood dust that comes into contact with the eyes can cause watering, soreness and inflammation of the eyes (conjunctivitis).
Level of Risk:
Most construction workers are at risk of COPD; studies find an elevated prevalence of COPD across many trades, and most trades have tasks that create dust or fumes. Many construction tasks have exposures to levels of dust which exceed the OSHA permissible exposure limit of 5 mg/m3 for non-specific dust. Because many construction trades work alongside each other, a construction worker can be over-exposed to dust generated by a co-worker doing a different task.
Some experts have suggested that dust at construction sites is best described as quartz (silica) containing mixed dust, and quartz is clearly one component of dust related to lung injury. The proportion of quartz in the overall dust exposure of any individual will vary by task, materials, specific years worked, work location, and likely other factors as well. Tuckpointing had respirable dust levels as high as 8 mg/m3 as an 8 hour TWA, with quartz levels as high as 1.7 mg/m3 as an 8 hour TWA. In one study that looked at both exposure and disease, workers with higher cumulative dust exposures were more likely to have a chest x-ray showing mixed dust pneumoconiosis (lung scarring due to an exposure to mixed dust). The prevalence of mixed dust pneumoconiosis was significantly increased after 25 years work at a tuckpointer or 33 years work as a concrete driller or grinder.
Studies of miners have shown that long term exposure to dust at levels of 2 mg/m3 causes COPD, and that as the silica content of the dust increases the total exposure needed to cause disease decreases. However, other dusts and fumes, including asbestos, cadmium and welding fumes also cause COPD, so silica is only one of the injurious components of construction dust.
One cross-sectional survey of pulmonary function was conducted among 220 pine and 354 maple wood workers, including low-exposure controls for each group. For the maple workers, two measures of reduced respiratory flow rates were significantly associated with high exposure, with odds ratios exceeding two. The findings were also similar for the pine workers indicating that both woods were associated with obstructive patterns of respiratory change.
Studies have shown a number of woods to be linked to allergic or hypersensitive respiratory disease (asthma-like symptoms), especially Western Red Cedar. Among 405 Red Cedar workers and 252 controls exposed to other wood dusts, Cedar workers has an increased prevalence over controls of several respiratory symptoms, rhinitis, and conjunctivitis.
Although there are limited contemporary studies, some literature has reported an association between nasal sinus adenocarcinoma and woodworking. From 1956-1965, the average annual incidence rate was about 0.7 per thousand for woodworkers compared to 0.6 per million in the general population. However, the authors futher note that there may have been possible chemical agents within the wood and proper ventilation was not common.
Bergdahl IA, Toren K, Erikson K, Hedlund U, Nilsson T, Flodin R, Jarvholm B. Increased Mortality in COPD among construction workers exposed to inorganic dust. Eur Respir J 2004. 402-406
Chan-Yeung, M., M.J. Ashley, P. Corey: A Respiratory Survey of Cedar Mill Workers I. Prevalence of Symptoms and Pulmonary Function Abnormalities. Journal of Occupational Medicine. 20(5): 323-327 (1978).
Ashley, M.J., P, Corey, M. Chan-Yeung, L. MacLean: A Respiratory Survey of Cedar Mill Workers II. Influence of Work-Related and Host Factors on the Prevalence of Symptoms and Pulmonary Function Abnormalities. Journal of Occupational Medicine. 20(5): 328-332 (1978).
Whitehead, L.W., T. Ashikaga and P. Vacek: Pulmonary Function Status of Workers exposed to Hardwood or Pine Dust. American Industrial Hygiene Association Journal. 42:178-186 (1981).
Acheson, E.D., R.H. Cowdell, E.H. Hadfield and R.G. Macbeth: Nasal cancer in Woodworkers in the Furniture Industry. British Medical Journal. 2:587-596 (June 8, 1968).
You must determine whether exposures at your jobs exceed allowable limits for overall dust and specific dusts.
Silica is an important component of many construction dust exposures., and the PEL for silica exposure in construction is much lower than the PEL for non-silica containing dust, so it is essential to determine the silica content of any dust exposures. OSHA has an e-tools site for silica that walks you through the process of assessment of silica exposure.
Exposure assessment must be done by a qualified person. You may be able to to obtain assistance in measuring exposures from your State OSHA consultation service or from your contractor association.
Regulations & Standards:
OSHA standard 1926.55, titled Gases, vapors, fumes, dusts, and mists, in safety and health regulations for construction must be in place. Exposure of employees to inhalation, ingestion, skin absorption, or contact with any material or substance at a concentration above those specified in the "Threshold Limit Values of Airborne Contaminants for 1970" of the American Conference of Governmental Industrial Hygienists, shall be avoided.
The current OSHA standard for overall dust which contain < 1% silica is 15 mg/m3. The NIOSH recommended exposure limit for crystalline silica is 0.05 mg/m3. NIOSH research shows that controlling exposures below this concentration should prevent all workers from obtaining silicosis. American Conference of Governmental Industrial Hygienists (ACGIH) recommends a time weighted average exposures of less than 10 mg/m3 for total dust. For respirable dust the ACGIH recommends a limit of 3 mg/m3 compared to an OSHA PEL for general industry of 5 mg/m3.
The Federal OSHA standard for non-specific total dust which contain < 1% silica is 15 mg/m3. This permissible exposure limit (PEL) also serves as a surrogate for wood dust exposure and 5 mg/m3 for respirable dust. However, the American Converence of Governmental Industrial Hygienists (ACGIH) has proposed a threshold limit value of 1 mg/m3for all wood species and 0.5 mg/m3 for Western Red Cedar.
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
Controlling worker exposure to dust also results in reductions in housekeeping or cleanup, reduced environmental contamination, and reduction in nuisance dust exposurers to the general public. Many cities and local governments have nuisance ordinances that may require dust controls.
There may be other hazardous substances that either grow or are treated on wood which can be mixed with wood dust such as:
- Molds and fungi
- Resin binders
- Paint stripper
- Glues and adhesives
- Waterproofing compounds
- Paints, lazquers, and varnishes
- Sealants, dyes, and bonding agents
These substances may also be attributable to cause skin, eye, and lung irritation, allergic reactions and occupational asthma. There are also several wood preservatives that are toxic and present cancer risks (creosote, pentachlorophenol [PCP] and copper arsenate).
Wood dust can create a combustible dust hazard.