Silica Background

Silica is a naturally occurring mineral in rock and soil. When inhaled, silica dust can cause silicosis, cancer and increases the risk of Tuberculosis (TB) infection. Airborne silica is present in numerous industries including construction, mining, foundry work, glass, concrete manufacturing, painting, pottery, and stone crushing.

In much of the developing world excessive exposures to silica dust are common in the stone crushing industry where most mills operate without dust controls. It is estimated there are over 12,000 stone crusher mills in India alone, which provide direct employment to over half a million workers, many of whom are disadvantaged women and children. The Indian Government estimates that 10 million people are exposed to silica dust on the job. Studies have shown increased morbidity and mortality among silica exposed workers from silicosis, lung cancer, TB, and other lung diseases.

Occupational exposure to silica dust in the mining industry is a global concern. The labor force in most developing countries is comprised largely of migrant workers and the attrition rates are high. Over one million mineworkers in China and 500,000 in South Africa have been diagnosed with silicosis. In southern Africa migrant workers in mineral mines experience higher rates of HIV and an associated TB incidence that is reportedly ten times that of the general population. India's mining industry provides employment to over 1.1 million people with thousands more employed in small, unofficial mines, but few are ever diagnosed with silica-related disease. The country's Supreme Court recently instructed the Indian Government to increase medial surveillance and to better compensate silicosis victims.

Link with Tuberculosis

Hazardous sandblasting by worker in Bangladesh.
(Photo Courtesy of Allison Joyce Photojournalist)

Sandblasting Jeans Causes Acute Silicosis

Sandblasting, a process that uses pressurized air to spray silica-containing sand onto a surface, is a method used to create a faded effect and soften the denim used for many styles of jeans. Sandblasting is known to cause silicosis and has been banned in many U.S. states and in some European countries. Safer substitute abrasive materials that do not contain silica are readily available, but are not routinely used on jeans.

In 2009, at least 600 textile workers in Turkey were confirmed to have silicosis and many more will remain at risk for years to come. Already 44 deaths from among these workers have been linked to silica exposure from sandblasting jeans. The situation in Turkey demonstrates that even short-term exposures to high levels of respirable dust during sandblasting is so intense that it can result in an acute form of silicosis. The exposure period for those diagnosed with silicosis in Turkey was less than 5 years with the disease progressing very quickly. Since the hazards of this practice were brought to the attention of the public through the media, sandblasting was banned in that country.

Despite the publicity from this situation in Turkey, the sandblasting of jeans appears to have migrated to other major garment producing nations, including Bangladesh, China, and India. Sandblasting is unregulated in these countries and much of the work is taking place in small, informal shops operating without dust controls. The majority of the workforce is unaware of the health hazards of this process.

In September of 2010, clothing companies Levi Strauss & Co and H&M announced a plan to eliminate all sandblasted garments from their product lines by the end of the year. Now it remains to be seen if this is the beginning of the end of this tragic story, or if this practice will continue with other brands taking up the slack.

Silica exposure has been linked with TB for over a century. Silica exposures in stone crushing mills in India have been shown to increase the risk of acquiring active Tuberculosis (TB) by nearly seven-fold. A study conducted in India of over one hundred former stone crusher workers showed that 48% had TB alone or in combination with silicosis. The risk is not limited to high burden TB countries as a recent study in Michigan showed that the individuals with silicosis had a 1,000 times greater incidence of TB than the general population. This link is even more significant as TB is the most common cause of death in those with silicosis.

Reducing exposures to respirable silica in the workplace would lead to a dramatic reduction in TB incidence among exposed populations. There are many other industries with excessive silica dust exposures including mining, ceramic and glass manufacturing, construction, and cement employing at least 230 million workers around the world. Most of the highest exposed individuals work in the informal sector, including more than 40 million artisanal small-scale miners operating in at least 80 countries.

The United Nations has recognized the need to establish programs to reduce TB among miners and other vulnerable workers exposed to silica dust. The UN declaration from the first ever General Assembly High-level Meeting on TB held in September 2018 called on countries to commit to “implementing primary prevention in high-risk occupations by reducing silica dust exposures in mining, construction and other dusty workplaces.”

OK International spearheaded this effort at the UN to recognize the need for TB prevention in the workplace. We estimate that 300,000 new TB cases can be prevented each year with appropriate workplace interventions.

International Silicosis Elimination Goal

The International Labour Organization (ILO) and World Health Organization (WHO) have responded to this public health crisis by launching an International Programme on the Global Elimination of Silicosis in 1995. The objective of the programme is to eliminate silicosis in all countries by 2030. Goals are achieved through international partnerships to raise awareness of the health effects of silica exposure and introduce appropriate technologies to reduce exposures.

Sign displayed at a stone crusher mill to raise awareness of dust hazards among workers.

India Program Description

As construction and road building is booming in India, small scale stone crusher industries are proliferating throughout the country, often in violation of air pollution and zoning guidelines. Airborne silica generated from these stone crushing mills throughout the Khurda region of Orissa, India are suspected to be the cause of increased morbidity and mortality rates from silicosis, cancer, and other lung disease. Unprotected workers including children working without respirators, proper ventilation, and dust suppression systems are subject to considerable health risks. Dust from these operations is also known to affect local communities. Without adequate screening for early detection of lung disease (virtually none exists), these workers often reach late-stage conditions prior to receiving care, at which point medical treatment is ineffective.

Starting in 2003, OK International formed a partnership with an Indian NGO, Jeevan Rekha Parishad (JRP), based in the State of Orissa to provide technical assistance to help reduce silica emissions from a cluster of stone crusher mills. We provided JRP with donated equipment to evaluate airborne exposures to silica and instructed the organization's volunteers and staff on proper use of the equipment. We then initiated a study to assess airborne silica exposures in stone crushing operations in this area and determined that silica exposures were approximately four times the regulatory level.

With a modest education and outreach efforts, our partners encouraged over 40 mill owners to install water spray systems to reduce silica levels in their operations. The results of this pilot program demonstrate reductions in average respirable silica of 80% after water spray controls were installed. The success of this pilot program suggests that relatively inexpensive modifications currently available in the local market can be effective at reducing silica exposures in stone crushing operations. We are now actively working to take this pilot project to a national level in India.

See our video Reducing Silica Exposures in Stone Crushing.

Silica released from stone crushing is causing an epidemic of silicosis, cancer, other lung diseases and increases the risk of acquiring Tuberculosis (TB). This situation is particularly dire in India where the stone crushing industry employs over half a million people, many of whom are women and children. Occupational Knowledge International (OK International) is providing technical assistance to small-scale stone crushing mills on how to reduce emissions in their operations. This video documents how they reduced silica exposures by over 80% in one pilot study.

For additional information on this project see: Reduction of Respirable Silica Following the Introduction of Water Spray Applications in Indian Stone Crusher Mills, Gottesfeld, P, Nicas, M, Kephart, J, Balakrishnan, K, and Rinehart, R., International Journal of Occupational and Environmental Health, Vol. 14, No. 2, 2008.

OK International has estimated the public health impact of introducing water spray systems in all stone crusher mills in India. Based on the exposures reductions we observed and epidemiological studies conducted in the U.S. we were able to make some conservative predictions. If this water spray technology were adopted in stone crushing mills throughout India, we estimate that it will prevent 90,000 cases of silicosis and 35,000 deaths from cancer and TB over the next 15 years.

See our Projects page to learn more about OK International's current silica reduction projects in India and project partners.