Developing a successful silicosis prevention strategy.

There are many potential sources of employee exposure to crystalline silica in a foundry, including sand handling, shakeout and grinding operations. Repeated exposure to respirable silica dust can lead to employees contracting silicosis and other lung conditions.

In recent years, significant emphasis has been placed on protecting foundry employees from exposure to respirable crystalline silica. This is partly due to OSHA's efforts aimed at reducing the current permissible exposure limit (PEL) for respirable silica by up to 50% (see sidebar below for more information).

This article represents the prevention strategies set up by the National Institute for Occupational Safety and Health (NIOSH) and the National Industrial Sand Assoc. (NISA), and takes an indepth look at their recommendations.

Getting Started

Implementing measures to reduce employee exposure to airborne dusts that contain silica below the acceptable levels is generally the most effective method of reducing the likelihood of employees contracting silicosis. These measures include engineering controls, improved work practices, training programs and respiratory protection programs. But before a foundry can institute a silicosis prevention plan, it must define the biggest risk areas in the foundry.

Personal exposure monitoring should be conducted by foundries to identify and evaluate problem areas, determine appropriate exposure controls and monitor performance. The evaluation also should help prioritize corrective measures, focusing on the highest exposed jobs first.

Chronic silicosis, the most common form of the disease, may go undetected for years while the disease is in its early stages. This fact highlights the need for routine exposure monitoring and follow-up corrective actions as a preventive method, Figure 1 provides a "to do list" for both workers and employers.

Educational Challenges

There are substantial educational challenges associated with silicosis prevention. One challenge is that airborne respirable silica dust is invisible to the human eye except in unique lighting situations. Foundry workers may not be as concerned about health hazards that they cannot see.

While larger particles tend to settle in the foundry building, the respirable particles remain airborne indefinitely due to natural and forced air currents that exist in all buildings. The airborne respirable particulate is therefore free to migrate within the foundry building and can also affect employees who are not directly working at or near their point of generation.

Approaching the Problem

In order to take a proactive stance on silicosis prevention, a foundry must establish priorities for control based on air sampling data, protecting potentially overexposed individuals with respirators during the period in which the evaluation is taking place. This exposure data-driven approach is not new to many segments of the foundry industry, as OSHA's standards for lead, cadmium and arsenic mandate the same approach.

Once air sampling data has been collected and problem areas identified, the main roadblock to identifying a suitable approach of silicosis prevention is organizational commitment and availability of resources. A solution to a problem this complex and multifaceted will only succeed if it has the full endorsement of both management and employees alike. An organized silicosis program can lead to better exposure control through upgraded performance of existing foundry ventilation systems.

Abrasive Grinding

One specific area of the foundry where protection of employees against respirable crystalline silica exposure continues to need attention is the ferrous foundry cleaning room. There, both high speed snag grinders (also known as pedestal or stand grinders) and the process of chipping and grinding with portable tools pose formidable issues.

Respirable sized particles are liberated when sand grains that are adhered to the casting surface are sheared into tiny particles by abrasive action. In the case of snag grinders, the liberated particles cling to the wheel, resist being drawn off by the exhaust ventilation applied to the grinder and are eventually stripped off by the casting. They are then projected into the grinder operator's breathing zone.

Exhaust ventilation systems serving chipping and grinding operations with portable tools only offer effective protection when the grinding swarf is directed at the exhaust hood opening. An alternative method--tool-mouthed hoods that are evacuated by a high velocity, low-volume exhaust--has not found acceptance in foundries because the hoods are bulky and disrupt the casting finishing operations.

Program Issues

One issue that can confuse silica exposure tracking is that the standards for airborne crystalline silica are expressed in two different forms that differ markedly from one another. Some states regulate exposure to respirable crystalline silica, while others regulate respirable dust that bears silica.

The airborne crystalline silica exposure is the most consistent parameter to track, because the silica content of foundry dust is typically well below 50%. When the tracking parameter is the entire respirable fraction of the dust, significant changes in other respirable dust components can confuse the focus of silica reduction programs.

There are multiple toxic forms of crystalline silica, including quartz, trydimite and cristobalite. Quartz is the most common in foundry environments. Cristobalite and trydimite, considered to be the more toxic forms of silica, are thermal transformation forms most often found in steel foundries and in furnace and ladle relining operations where silica is exposed to significantly higher temperatures. OSHA has published a guidance document to allow the proper assessment of exposure limits that include multiple forms of respirable silica.

There also is more than one type of personal sampling cyclone in use. Use of different cyclone types for air sampling can potentially result in significant variations in measured respirable silica concentrations. The most consistent approach for a foundry to take in its silicosis prevention program is to conduct all air sampling using one type of cyclone.

Because exposure monitoring for silica is relatively expensive, it is neither feasible nor necessary to frequently sample each and every foundry worker. Although variability among individual work practices suggests that every worker's exposure should be scrutinized at some point, the majority of the data necessary to shape an appropriate silicosis prevention program can be developed by job category, with priority in the number of samples given to jobs with documented higher exposures.

While the human lung has excellent dust-clearing mechanisms, the ongoing damage that occurs when sharp, respirable crystalline particles permanently imbed themselves in the alveolar walls can be dangerous. The issue is a chronic one, and progress toward silicosis prevention is best made by people who are concerned about long-term health. This issue must be addressed by all--from the CEO to the last-hired cleaning room worker.

For More Information

Visit www.moderncasting.com for "Silica Risk Assessment," W.B. Bunn III, 8th AFS Environmental Health and Safety Conference, 1997, p.223-251.

"Silica...Information for Metalcasters," AFS Safety & Health Committee 10-Q, AFS (2001).

Fig. 1

NIOSH Provides This "To Do List" for Workers and Employers


To prevent silicosis, workers can:
* Work with employers;
* Use controls in place to reduce dust levels and maintain those
  levels. Notify employer if controls are not functioning
  properly;
* Use alternate methods to compressed air, such as vacuum
  and/or water for cleaning;
* Suggest the use of nonhazardous materials to replace silica;
* Correctly wear respirators when required;
* Participate in air monitoring, medical surveillance and
  training programs;
* Ask your employer questions as needed and make certain to
  review all test results.

To prevent silicosis, employers can:
* Commit to preventing silicosis;
* Comply with regulatory requirements, especially as regards
  engineering controls and personal protection;
* Perform air monitoring to select and ensure the effectiveness
  of engineering controls, select proper respiratory protection,
  assure that work practices are effective and determine if a
  medical surveillance program is necessary;
* Practice preventative maintenance;
* Substitute less hazardous materials for crystalline silica;
* Train workers on health effects, engineering controls, work
  practices and the importance of housekeeping and maintenance.
  Make certain workers know operations and materials pose a
  hazard;
* Provide medial examinations per National Institute for
  Occupational Safety and Health (NIOSH) recommendations. Develop
  a plan for reducing exposures of employees whose x-rays show
  changes consistent with silicosis.

National Institute for Occupational Safety and Health (NIOSH)

RELATED ARTICLE: OSHA Silica PEL Update

While OSHA has been working on developing a comprehensive silica standard for several years, the current permissible exposure level (PEL) for silica remains at 0.1 mg/cu m. OSHA formally announced its intention to adopt a comprehensive silica standard, with a potentially very stringent PEL, in 1997. At that time, the agency was expected to recommend at least a 50% reduction in the current PEL.

According to the U.S. Dept. of Labor's latest semiannual regulatory agenda published in May, OSHA plans to move on the issue of exposure to crystalline silica. The agency says crystalline silica remains a "serious threat" to more than two million U.S. workers, including 100,000 high-risk jobs in abrasive blasting, foundry work, stonecutting and tunnel work. In addition, the agency points to recent studies that indicate a statistically significant increase in lung cancer among silica-exposed workers.

While no formal action is expected until early 2003, a significant reduction in the PEL could have a devastating impact on the foundry industry. Many foundries would need to install new air exhaust systems, at a cost of at least $500,000, with no guarantee of meeting the 50% reduction. This expense could force a number of foundries into a noncompetitive pricing situation. A standard will likely include provisions for product substitution, engineering controls, training and education, respiratory protection, record keeping, medical removal, and medical screening and surveillance.

Based on conversations with agency officials, OSHA would like to get a final silica standard out the door before the end of the Bush Administration through some type of negotiated rulemaking process, whereby the interested parties would present OSHA with a consensus proposal that the agency could turn into a comprehensive silica standard. AES also will continue to interact with key agency officials on this issue.

--Stephanie Salmon, Waterman & Assoc.

Silicosis--It's Preventable

MODERN CASTING sat down with Bob Glenn, president, National Industrial Sand Association (NISA), Calverton, Maryland, to discuss the best methods of preventing silicosis.

Is silicosis a continuing problem?

While progress has been made in reducing the disease over the past thirty years, we unfortunately still have cases developing where silica dust is not being adequately controlled. While one death from silicosis is one too many, data from the National Center for Health Statistics shows progress--deaths attributable to silicosis have been reduced from 351 in 1970 to 93 in 1998."

What is the key to preventing silicosis?

"It is simply controlling a worker's exposure to silica dust to safe levels. Silicosis is a chronic disease that generally takes 20 yr of exposure to dust above the OSHA permissible exposure limit (PEL) to develop. Unfortunately, there are still workplaces where exposure day-in and day-out are above the PEL. It is these operations where long-term exposed workers are apt to develop chronic silicosis."

What has NISA done to prevent silicosis?

"NISA has developed a Silicosis Prevention Program and adopted a goal of preventing the development of new cases of silicosis in its member company employees. The elements of the program include commitment by member companies, implementation of the NISA Occupational Health Program for Exposure to Crystalline Silica, assessment of dust exposures, medical surveillance of workers, control of silica exposures through engineering and other control measures, employee involvement in the prevention program, and implementation of smoking cessation programs. NISA and its members firmly believe that the goal of prevention of silicosis is attainable. However, the achievement of the goal requires a constant, vigilant effort on the parts of many people."

About the Author

Robert C. Scholz is the program manager--industrial ventilation at RMT, Inc., Brookfield, Wisconsin. He has 32 yr of experience in ventilation systems design in metallurgical industries.

Jeet Radia is the senior vice president at Keramida, Inc., Columbus, Ohio. He has over 25 yr experience in industrial hygiene and air pollution control engineering for foundries.