Objectives. We describe an emerging public health concern regarding silicosis in the fast-growing highway repair industry.
Methods. We examined highway construction trends, silicosis surveillance case data, and environmental exposure data to evaluate the risk of silicosis among highway repair workers. We reviewed silicosis case data from the construction industry in 3 states that have silicosis registries, and we conducted environmental monitoring for silica at highway repair work sites.
Results. Our findings indicate that a large population of highway workers is at risk of developing silicosis from exposure to crystalline silica.
Conclusions. Exposure control methods, medical screenings, protective health standards, and safety-related contract language are necessary for preventing future occupational disease problems among highway repair workers. (Am J Public Health. 2004;94:876-880)
The United States is currently engaged in a massive public works effort to repair the national highway system's deteriorating infrastructure.(
Because the interstate system is nearly completed, the focus has shifted from constructing new highways to preserving and improving existing highways. Much of the pavement on the interstate system was constructed 20 to 40 years ago, with some older highways having been incorporated into the system. Data on interstate pavement condition are taken from the Highway Performance Monitoring System (HPMS) and are used to track the condition and the performance of US highway systems. The 1994 HPMS report to Congress (the most recent) showed that more than half of the highway system's pavement was rated as fair to poor, indicating a need for resurfacing or other rehabilitation in the near future.(
Traditional methods of highway surface repair involved patching damaged areas with asphalt, an approach that usually resulted in failure within months of the repair. In the mid-1980s, a new method of cut-and-repair road maintenance that uses newly developed quick-setting concrete material, resulted in more permanent repairs. This new method utilizes large crews to cut, break up, and remove large sections of concrete road before patching begins. These operations, sometimes completed during overnight work shifts, result in the generation of large amounts of dust.
Our article describes the potential risk of silicosis for workers in the fast-growing highway repair industry. We reviewed silicosis surveillance data from the National Institute for Occupational Safety and Health (NIOSH) Sentinel Event Notification System for Occupational Risks (SENSOR) and crystalline silica exposure data from highway repair projects collected during the 1999 road construction season.
Silicosis is a disabling, nonreversible, and sometimes fatal lung disease caused by inhaling dust containing extremely fine particles of crystalline silica.(
The dangers of silica exposure and silicosis are well established in the mining,(
The NJDHSS maintains a registry of reported silicosis cases and collects the medical and occupational data necessary for determining whether a case meets an epidemiological case definition. Cumulative data on silicosis are collected and are analyzed by NIOSH to determine incidence, causes, and trends of the disease. An integral component of the New Jersey surveillance system for silicosis is the follow-up of work sites identified through case reports. NJDHSS industrial hygienists conduct on-site evaluations, assess the risk of exposure to silica, and recommend control measures to prevent exposure.
The NJDHSS began a hazard surveillance project in 1998 to investigate highway repair as a possible source of silica exposure. Interest in this industry stemmed from a sentinel case of silicosis identified by NJDHSS in 1993. The case involved an individual who worked for 2 road construction companies from 1955 to 1990. This person was 63 years old when he was first diagnosed with silicosis. His work history indicated exposure to silica dust without respirator use during highway-building activities. Although the sentinel case pointed to exposure as a result of building roads versus repairing highways, a link between the highway construction industry and silica exposure was established. A review of the Occupational Safety and Health Administration's (OSHA) Integrated Management Information System database revealed that few data were available on silica exposure from highway construction. A pilot project was initiated with the New Jersey Department of Transportation (NJDOT) to perform industrial hygiene air sampling at highway repair sites. Air sampling was performed at a bridge deck repair site during the 1998 summer construction season; levels of silica dust indicated that workers were potentially overexposed.
In January 1999, the New Jersey Silica Partnership (Table 1) was formed to address issues associated with silica exposure among New Jersey road and highway workers. The primary goal of this effort was to quantify silica exposure from dust-producing tasks undertaken during road construction and repair work. The silica exposure data were used to support the development of protective language for NJDOT contracts similar to the health and safety language for reducing lead exposure that currently appears in NJDOT contracts for overpass- and bridge-painting operations.
The materials used to build roads, such as concrete, asphalt, and masonry products, contain silica sand as well as other types of crystalline silica. Road construction and repair workers are potentially exposed to airborne silica dust from activities that create airborne dust, such as sawing, breaking, and grinding concrete and other materials that contain silica.
We reviewed all confirmed silicosis cases from the New Jersey, Michigan, and Ohio silicosis registries containing work histories coded with construction Standard Industrial Classification (SIC) codes(
In April 1999, NJDHSS industrial hygienists began a 6-month effort to collect air-sampling data for various tasks performed in road construction and repair. A protocol was developed and was distributed to 10 contractors who had been awarded highway repair contracts from the NJDOT Personal samples of respirable crystalline silica dust were collected at a flow rate of 1.7 L/min with a battery-operated sampling pump. The pump was attached to the employee's waist and was connected via Tygon tubing to a preweighted 37-mm, 5-pm pore-size polyvinyl chloride filter in a filter cassette; a 10-mm Dorr-Oliver nylon cyclone was placed in the employee's breathing zone in accordance with NIOSH method 7500.(
At each worksite survey, workers involved in specific highway repair tasks were selected for silica air sampling. These dust-producing tasks were targeted after discussions with the contractors and the industrial hygienist's visual observation of dust generated from the various tasks during the initial survey. Eight-hour time-weighted-average sample results were compared with exposure standards established by OSHA and the American Conference of Industrial Hygienists (ACGIH) for crystalline silica. The OSHA permissible exposure limit (PEL) varies from 0.1 mg of respirable dust per cubic meter of air (mg/m³) to almost 5 mg/m³ depending on the percentage of crystalline silica in the dust. In 2000, the ACGIH adopted a threshold limit value (TLV) of 0.05 mg/m³ for respirable crystalline silica.(
Five hundred seventy-six confirmed silicosis cases in New Jersey, Michigan, and Ohio were reported to NIOSH for the years 1993 through 1997. Silicosis cases were identified by first determining potential silica exposure from the work history; then confirmation was obtained through either a positive chest x-ray reading for silicosis by a NIOSH certified "B reader" or a medical record radiology report with findings consistent with Silicosis.(
Industry, occupation, age at diagnosis, year of first exposure, and duration of exposure for silicosis case reports under SIC 16 are shown in Table 2. Five of the 12 SIC 16 cases (42%) involved work in runnel construction. Three cases (25%) specifically identified road construction and maintenance as the primary source of exposure. The New Jersey road-construction case indicated new-highway construction in which exposure began in the 1950s, well before the introduction of the modern cut-and-patch repair method. Case 1 in Ohio occurred in a laborer with an 8-year duration of work involving the use of a jackhammer on bridge surfaces, although no information was provided about when exposure occurred. Road maintenance was listed as the occupation on the death certificate for case 2 in Ohio but no data were provided on year of first exposure or duration of exposure. Two cases in Michigan potentially involved road construction; again, however, the work histories were incomplete.
Monitoring for airborne crystalline silica was completed for 9 highway repair sites involving 7 contractors. These contractors were listed according to the following Dun & Bradstreet MarketPlace industry classifications: concrete construction (roads, highways, sidewalks; SIC codes 1611-0202), general contractor (highway and street construction; SIC codes 1611-9901), and highway- and street-paving contractor (SIC codes 1611-0204). A total of 52 samples were collected for 7 of the 9 typical tasks: operating a jackhammer, sawing concrete, milling concrete, cleaning up concrete, drilling dowels, milling asphalt, and cleaning up asphalt. Samples were not collected for scabbling (small-scale surface milling) and grooving (surface depth cutting). The percentage of crystalline silica contained in the dust of an air sample was used to calculate the OSHA PEL for each respective sample.
Airborne levels of crystalline silica associated with 7 major road repair tasks are shown in Table 3. Sample results indicated a significant risk of overexposure to crystalline silica for workers who performed the 5 highway repair tasks involving concrete. Mean sample results for these 5 tasks exceeded the ACGIH TLV for crystalline silica. Sample results in excess of the OSHA PEL were found for operating a jackhammer (88% of samples), sawing concrete and milling concrete tasks (100% of samples); cleaning up concrete tasks (67% of samples); and drilling dowels (100% of samples). No measured exposures in excess of the PEL were found for milling asphalt and cleaning up asphalt; however, of the 8 samples collected for milling asphalt, 6 (55%) results approached the OSHA PEL, and 1 was at 92% of the PEL. The percentage of samples exceeding the more stringent ACGIH TLV was even greater. No dust-control measures were in place during the sampling of these highway repair operations.
Large-scale public works projects and silicosis share a common history. For example, the Hawk's Nest disaster(
Occupational disease surveillance case data from the New Jersey, Michigan, and Ohio SENSOR programs indicate that workers employed in certain occupations in the construction industry are at risk of developing silicosis. The disease evidence is less clear for highway construction workers, because the majority of identified cases in this group occurred in individuals working in tunnel construction. Only 3 (7%) of the 45 SENSOR-reported silicosis cases in the construction industry between 1993 and 1997 had work history data identifying exposure specific to highway construction work. A sentinel-event surveillance system such as SENSOR is limited in its ability to detect a long-latency chronic disease among the worker population because of the relatively short time that modern highway repair methods have been in use. This lack of sensitivity in identifying silicosis among a newly exposed population demonstrates the importance of using hazard-surveillance methods to identify populations at high risk and to target preventive interventions. Hazard surveillance refers to the ongoing assessment and evaluation of hazardous substance use in the workplace and of worker exposure to these hazardous materials.(
Concrete disturbance and removal during highway repair projects generate high levels of airborne crystalline silica dust However, highway worker exposure to crystalline silica is variable. Highway repair work is conducted in an open-air environment in which weather conditions can affect exposure levels. Intense exposure can potentially occur when larger-scale projects are conducted in an assembly-line fashion and when tasks that generate dust, such as operating a jackhammer or sawing concrete, are performed continuously for a full 8-hour shift. Conversely, crews that work on small road-repair projects spend about half the shift removing the existing concrete and the remaining time doing relatively dust-free patch work, resulting in lower overall exposures to silica dust. A highway worker who performs a non-exposure task (e.g., a flagman) can potentially be exposed to dust generated by other tasks performed nearby. The amount of highway repair work contracted to a specific contractor is dependent on available projects and successful bidding. Companies involved in this type of work also specialize in types of construction work not involving concrete. Thus, employees may be exposed to silica dust on only an intermittent basis. Also, the highway worker may be a general laborer who is involved in other work than highway repair. Highway repair methods may vary in different parts of the country; for example, the Connecticut Department of Transportation will sometimes require the use of water to control dust during construction work. New Jersey projects do not use water because of potential problems with construction material performance, environmental concerns with slurry runoff, costs associated with vehicle cleanup and paint damage claims from passing motorists, and concerns about hazardous driving conditions on wet roadways.
The air-sampling results in Table 3 show levels of respirable silica dust above the OSHA PEL for 6 of the 8 tasks performed during highway repair. For typical tasks such as operating a jackhammer and sawing concrete, average silica exposures approached 3 times the regulatory limit, whereas sample results for milling concrete were more than 10 times fills limit. Exposures were dramatically higher than the limits established by ACGIH for protection against silicosis. The recently adopted ACGIH TLV is at most one half the current OSHA PEL. One must consider that the OSHA PEL for crystalline silica is based on outdated toxicological information from the late 1960s. OSHA has placed crystalline silica on its Semi-annual Regulatory Agenda (in the proposed role stage(
The various exposure limits for crystalline silica have been established to prevent silicosis, but they do not address the risk of cancer associated with crystalline silica exposure. The International Agency for Research on Cancer has designated inhaled crystalline silica as a Class I carcinogen,(
To reduce worker exposure, future activities addressing the silica exposure hazard must focus on prevention. Research on concrete, stone, and masonry jobs that involve drilling and sawing has demonstrated the efficacy of water in reducing dust levels to which workers are exposed.(
Continued research is needed to confirm the link between silicosis and highway repair work. Modern highway repair methods did not begin until the mid-1980s, and jobs that utilize these methods are increasing in number as the nation's highway infrastructure is rebuilt. A cohort of high-risk highway repair workers with long-term exposures could be medically screened for silicosis to further evaluate the disease potential among this occupational group.
The NJDOT has implemented a proposal to include silica safety and health language in highway repair contracts similar to the language for lead exposure in contracts for bridge-painting projects. This strategy has worked especially well in reducing lead levels in the blood of workers who are involved in bridge-painting operations.(
Requests for reprints should be sent to David J. Valiante, MS, CIH, NJ Dept of Health and Senior Services, Occupational Health Surveillance Program, Trenton, NJ 08625 (e-mail: david.valiante@doh.state.nj.us).
This article was accepted May 11, 2003.
D.J. Valiante conceived the project and wrote the article. D.P. Schill directed the project and helped analyze the data. K.D. Rosenman helped conceive the project, and E. Socie reviewed interim data and provided data analysis. All authors provided substantive contributions to the article.
The disease surveillance component of this project was both reviewed and approved by the institutional review board of the New Jersey Department of Health and Senior Services. The environmental evaluation component of the study was exempt from institutional review board approval because no personal identifiers were involved. No informed consent was obtained, because study participants were not enrolled.
This work was supported by the National Institute for Occupational Safety and Health (NIOSH) under the Sentinel Event Notification System for Occupational Risks Program to conduct surveillance for occupational disease.
We would like to thank Helga Fontus, Michael Coyne, and Devendra Singh of the NJ Dept of Health and Senior Services and Mark Wadiak of the NJ Dept of Labor for their help with this project. We also wish to acknowledge David Ippolito, Area Director, and Kris Hoffman, Assistant Area Director, NIOSH's Parsippany Area Office, for both their leadership and their vision in making the New Jersey Silica Partnership a successful reality.
NJ Dept of Health and Senior Services
NJ Dept of Transportation
NJ Dept of Labor, OSHA Onsite Consultation Service
Federal Dept of Labor, OSHA
NIOSH, Division of Respiratory Disease Studies
NIOSH, Division of Engineering Control Technology
Utility and Transportation Contractors Association
Association of General Contractors
Laborers' Health and Safety Fund of North America
Laborers' International Union, Locals 172 and 472
NJ State Safety Council
Ten different highway construction contractors
Note. OSHA = Occupational Safety and Health Administration; NIOSH = National institute for Occupational Safety and Health.
By David J. Valiante, MS, CHI; Donald P. Schill, MS; Kenneth D. Rosenman, MD and Edward Socie, MS
David J. Valiante and Donald P. Schill are with the New Jersey Department of Health and Senior Services, Occupational Health Surveillance Program, Trenton, NJ. Kenneth D. Rosenman is with the Department of Medicine, Michigan State University, East Lansing, Mich. Edward Socie is with the Ohio Department of Health, Columbus, Ohio.