Understanding a complex killer

  • Photo courtesy of the National Institute of Safety and Health.
  • Any employee involved in installing the roof system in NIOSH's study, whether involved in cutting tiles or not, had the potential for overexposure to respirable silica and noise.
Photo courtesy of the National Institute of Safety and Health.
  • Exposures from cutting cement roof tiles can exceed OSHA's PEL.
Photo courtesy of the National Institute of Safety and Health.

"I was there diggin' that tunnel for six bits a day; didn't know I was diggin' my own grave. Silicosis eatin' my lungs away."—"Silicosis is Killin' Me," Alan Lomax

Respirable silica, a material present in cement construction products, including roof tiles, has been a known occupational health hazard for more than a century. However, because symptoms associated with respirable silica often mimic other diseases, silicosis, the disease caused by respirable silica, often is misdiagnosed. The National Institute for Occupational Safety and Health (NIOSH) has undertaken studies to determine how to protect roofing workers from suffering deadly diseases related to respirable silica.

The first large-scale incident related to respirable silica in the U.S. was the Hawk's Nest Tunnel disaster in 1920-30. In 1920, a Union Carbide subsidiary won a contract to build a hydroelectric project in the mountains of West Virginia. Workers primarily were poor locals and newly arrived African Americans from the South. Wearing no protective gear, 476 men digging a tunnel though a mountain died from acute silicosis. The mountain later was found to contain rock that was 99.7 percent silica.

Outcry about the deaths led to a Congressional hearing regarding the incident in 1935 during which it was stated such blatant abuse of workers was "hardly conceivable in a democratic government in the present century."

The hearings resulted in legislation to compensate the sickened workers and protect future ones. Newspapers interviewed many families who stated they had lost all their male members who worked in the tunnel to acute silicosis.

What is it?

Silica, an element that makes up about 12 percent of the Earth's crust, comes in many forms. The most familiar of these is silicon dioxide, otherwise known as sand. There are two main types of silica: amorphous (as in glass) and crystalline. Types of crystalline silica are quartz, cristobalite and tridymite. Sand, which contains quartz, is a major component of cement.

Beach sand is not considered hazardous because the silica crystals are too large to inhale. However, as particle size decreases, the ease of inhaling particles increases. Silica particles less than 10 micrometers across (less than one-fifth the diameter of a human hair) can be inhaled and deposited deep within the lungs. Particles of this size are respirable. Respirable silica forms when material containing crystalline silica is mechanically altered by methods such as blasting, drilling and cutting.

Inhaling respirable silica can cause silicosis, a permanent lung disease that has no cure but is completely preventable. Silicosis is thought to be the result of a chronic inflammatory response caused by silica crystals in the lungs. The initial inflammatory response is the body's way of alerting the immune system to remove a foreign substance. But because cells cannot destroy the silica particles, the particles accumulate within a cell. When a cell becomes so full of silica it no longer can function, it dies.

Upon a cell's death, the ingested silica crystals are re-released into the lungs, and the process starts over again. This chronic inflammatory response forms scar tissue. As normal lung tissue is replaced by scar tissue, symptoms such as shortness of breath, fatigue and chest pain may occur. Breathing may become so difficult that even walking on level ground becomes tiresome. The length of time from initial exposure until there is clinical evidence of silicosis depends on the level and duration of silica exposure, but it typically is 10 years to 20 years or longer. The disease may progress even after exposure stops because silica cannot be removed from the body and will continue to provoke an inflammatory response.

Silicosis has been associated with other connective tissue diseases such as rheumatoid arthritis, scleroderma, lupus and sarcoidosis. In addition, it has been linked with various kidney disorders.

Up to half the people who have silicosis develop tuberculosis or similar mycobacterial infections because the body's cells that usually fight off these bacteria have been disabled or killed from trying to get rid of the silica crystals. Having silicosis also puts people at increased risk for lung cancer. Treatment consists primarily of supportive care, which could include supplemental oxygen, inhaled medications and periodic testing for tuberculosis infection.

NIOSH conducts Health Hazard Evaluations (HHEs) to investigate potential workplace hazards and make recommendations to reduce exposure and prevent disease. During NIOSH's HHEs regarding respirable silica exposure to roofing workers, investigators found most workers did not realize they were exposed to hazardous silica in the dust generated during the dry cutting process. If employees are unaware of the exposure, it is unlikely their physicians will ever recognize it. Without the history of occupational exposure to respirable silica, a physician might not consider silicosis as a diagnosis.

The inability to diagnose the disease early in the process without a complete occupational history may contribute to an underestimation of the number of silicosis cases in the U.S. It is likely many silicosis cases are misdiagnosed as emphysema, interstitial lung disease or other lung problems when employees don't accurately relate their workplace exposures to physicians. In the U.S., work-related silicosis causes about 200 known deaths per year. About 1 million workers are exposed to respirable silica every year. It is unknown how many roofing workers have died from or been disabled by silicosis.

Regulatory requirements

In 1996, the Occupational Safety and Health Administration (OSHA) published a Silica Special Emphasis Program that outlined the sampling methods and medical screening protocol required at any workplace that exposes its employees to respirable silica above the permissible exposure limit (PEL). OSHA defines the respirable silica PEL by a formula found in its Construction Standard 1926.55. Each OSHA-approved state plan enforces the PEL at a minimum. Alternatively, states may have their own standards as long as they are as stringent as the construction standard PEL. Contact your state OSHA office to find out how it enforces occupational exposures to respirable silica.

The Special Emphasis Program mandates pre-placement medical examinations, lung function testing and chest X-rays for employees who may be exposed to silica at or above the PEL. These tests are to be repeated at regular intervals and upon employment termination. A chest X-ray that is positive or consistent with silicosis requires immediate participation in a respirator program (including all components described in OSHA 1910.134, such as annual fit testing and training on respirator use, storage and care) or placement of the employee in a nonsilica work environment.

Employers must retain employee records, including the medical testing results, for 30 years post-termination because of the long latency period for silicosis. In silicosis cases, it helps doctors to see the changes in the X-rays and lung function testing over long time periods. Early testing enables doctors to note the subtle changes that may mark the onset of the disease and track the disease's course. Because silicosis also is a risk factor for lung cancer, periodic chest X-rays may aid in detecting this malignancy early, as well.

Roofing issues

In 2003, NIOSH received a request from the roofing union to conduct an HHE of employees of a residential roofing contracting company in Phoenix. The union was concerned employees were exposed to silica dust when dry cutting cement tiles with handheld, gas-powered saws during the roof system installation process. NIOSH conducted an investigation to measure respirable silica, noise and carbon monoxide exposures of employees installing roof systems.

The HHE results indicate any employee involved in installing the roof system in the study, whether involved in cutting tiles or not, had the potential for overexposure to respirable silica and noise. The measurements showed employees' exposures exceeded OSHA's PEL and NIOSH's recommended exposure limit (REL) for respirable silica and noise. The PEL is a legally enforceable limit; the REL is a recommendation. Respirable silica levels for seven of the 16 employees sampled (44 percent) exceeded OSHA's PEL. Fourteen of the 16 samples (88 percent) exceeded NIOSH's REL. NIOSH investigators recommended substituting tiles that do not contain silica for the cement tiles, putting in place engineering controls, and exercising administrative controls to reduce or eliminate the overexposures. Engineering and administrative controls include using wet cutting methods and local exhaust ventilation and isolating cutting to a stationary site on the ground. Immediate implementation of a mandatory respirator program was recommended until one or more of the recommended controls were proved effective.

In late 2004, NIOSH received three additional HHE requests to investigate respirable silica and noise exposures among other roofing contractors in Phoenix. Sampling at these additional worksites again revealed overexposures. In response, NIOSH medical personnel set up a silicosis screening program in February 2005. More than 100 employees from the four companies involved in the HHEs completed a medical questionnaire and had lung function testing and chest X-rays. Results from the medical screening program are pending. Results should be available in early 2006.

Interim program

Until engineering controls and work practices are shown to reduce exposures below occupational exposure limits, you should make sure roofing workers wear respiratory protection and take part in a respiratory protection program that conforms with OSHA 1910.134.

Respirable silica sampling results indicate employees working with cement tile should wear, at a minimum, a half-mask respirator. Half-mask air-purifying respirators have an assigned protection factor (APF) of 10, which means they can be used by employees when exposures are less than or equal to 10 times the occupational exposure limit (considering the NIOSH REL of 0.05 mg/m³, this equates to a concentration of less than or equal to 0.5 mg/m³). Respirators at a higher APF, such as full-face air-purifying respirators (APF = 50) or a powered air-purifying respirator with a loose- or tight-fitting face piece (APF = 25) also can be considered. Ease of use, reuse, disposability and safety issues must be considered for respirator selection.

Controlling exposure

The best way to control silica exposure is through material substitution. However, cement tile manufacturers have informed NIOSH of concerns about the added cost of product substitution and product reliability if the sand content of cement is replaced with another material. Until product substitution can be achieved, several controls, such as wet cutting, local exhaust ventilation, stationary cutting stations and pre-scoring tiles during the manufacturing process are being investigated by NIOSH and roofing contractors to determine their viability.

Find out more

NIOSH offers many educational materials about respirable silica exposure and silicosis available to the public for free. This information can be obtained from NIOSH's Web site at www.cdc.gov/niosh/homepage.html or by calling (800) 35-NIOSH (356-4674).

Judith Eisenberg is a physician with NIOSH's Hazard Evaluation and Technical Assistance Branch. Ron Sollberger is an industrial hygienist with the same branch.


The National Institute for Occupational Safety and Health (NIOSH), established in 1970 by the Occupational Safety and Health Act, is a research agency within the Centers for Disease Control and Prevention in the Department of Health and Human Services. NIOSH's primary mission is to conduct research and provide education in occupational health and safety.

Unlike the Occupational Safety and Health Administration (OSHA), which is in the U.S. Department of Labor, NIOSH is a nonregulatory agency. NIOSH manages a congressionally mandated program, the Health Hazard Evaluation (HHE) program, to investigate potential workplace hazards and recommend ways to reduce exposure and prevent disease. Requests for HHEs can come from management, employee representatives or employees. Additional information regarding the HHE program and HHE request forms is on NIOSH's Web site, www.cdc.gov/niosh/hhe.

The alarm bell sounds

by Tom Shanahan, CAE

There are many obvious safety and health-related hazards in the roofing industry, such as falls, burns and back injuries. Other more application-specific health and safety concerns, such as exposure to coal-tar fumes and dust, asphalt fumes, propane gas and adhesives, also are well-known. However, silica exposure in roofing operations somehow only surfaced as a possible health issue recently.

NRCA first became aware of the silica issue in January when the National Institute for Occupational Safety and Health's (NIOSH's) Judith Eisenberg contacted NRCA about presenting her research findings regarding roofing worker exposure to silica at the 2005 International Roofing Expo. Eisenberg was given the opportunity to present her findings during the expo. Attendance at her program was sparse, yet the information she presented was compelling—she saw excessive silica exposure as a result of roof tile cutting operations.

NRCA was asked by the United Union of Roofers, Waterproofers and Allied Workers (UURWAW) to attend a meeting to discuss the issue in Phoenix on March 9. The attendee list was a Who's Who from the safety field, including representatives from the Occupational Safety and Health Administration's (OSHA's) national, Region 9 and local area offices; medical, industrial hygiene and safety representatives from NIOSH; representatives from the Center to Protect Workers' Rights; representatives from UURWAW's national and local offices; representatives from the National Association of Homebuilders' national and local offices; representatives from two roofing tile manufacturers; four roofing contractors; NRCA representatives; Arizona Roofing Contractors Association representatives; and Associated Roofing Contractors of the Bay Area Counties representatives.

The end result of the meeting was clear. NIOSH data showed typical roof tile cutting operations created silica exposures in excess of OSHA's permissible exposure limit. Work has to be done to determine how best to ascertain the silica exposure risk in the field and what work practices to employ when it is present. Neither will be an easy endeavor. And the work has to be done quickly because roofing contractors are at risk of OSHA citations and worker exposure.

NIOSH agreed to conduct testing and expects to have results from its worker research available in early 2006; NRCA hopes the report will provide more information about field exposures.

As a result of the meeting, a working group was established to debate and identify practical work practices to effectively reduce exposures. Basically, the working group represents one person from each of the organizations represented at the March 9 meeting. An initial meeting was held, and some progress was made identifying some basic work practices though nothing formal has been released. For example, it is known that simply stepping out of the dust cloud and/or using engineering controls, such as wet methods and vacuuming, will significantly—if not completely—reduce exposures. Still, on a roof, these options aren't as easy as they sound and can create some serious additional safety hazards.

It was reassuring that the tenor of the March 9 meeting not only was one of concern but also of a sincere desire to identify workable solutions to this situation. On an important note, OSHA representatives stated the agency will not issue citations for silica exposures in roofing until the group's work practices are identified and accepted. To date, this has held true. NRCA will keep members and the industry informed of any developments regarding this issue.

Tom Shanahan is NRCA's associate executive director of safety and risk management.


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