We have been using fiber cement siding but are growing concerned with the exposure to crystalline silica that is typical in most products.


We have been using fiber cement siding but are growing concerned with the exposure to crystalline silica that is typical in most products.

Asked by John Dalzell

Crystalline silica is now known to cause cancer when inhaled as a dust which is common when these products are cut, drilled or otherwise worked.

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Cynthia Phakos's picture

As a contractor that is installing this everyday you would be well advised to follow all of theguidelines recommended by OSHA. Wikipedia's entry on Silicon Dioxide states:

  • Inhaling finely divided crystalline silica dust in very small quantities (OSHA allows 0.1 mg/m 3)over time can lead to diseases of the lungs as the dust becomes lodged and continuously irritatesthem, reducing lung capacities.

  • This effect creates an occupational hazard for people workingwith materials that contain powdered crystalline silica and so on.

Children, asthmatics of any age, allergy sufferers, and the elderly (all of whom have reduced lungcapacity) can be affected in much less time.

Crystalline Silica

Silica is a compound found in nature made up of silicon and oxygen atoms and exists in anon-crystalline and crystalline state. Plentiful on all continents, the most prevalent sourceis in alpha quartz which can be an igneous, sedimentary and metamorphous type rock.

Crystalline Silica is also a component found in sand, in its eroded state.


Crystalline Silica is used in many industries from fiber optics to electronics. Its primaryuse is in making glass which dates back 5,000 years but was also used in pottery, cementand other materials where sand is added.

Today, the glass industry uses a highly, refinedcrystalline silica with less than 0.03% iron and a fine silica powder is now used in ceramics,pottery and china.

Today, crystalline silica is used not only in Fiber Cement Board, but in many severalconstruction products including Gypsum Board, Joint Compound, and Fireproofing to name afew.

Health Issues

With the Industrial Revolution and the invention of the pneumatic hammer in 1897, higher levelsof dust exposure caused severe respiratory diseases, shortening the lives of workers. In 1915, theBritish physician Edgar Collis identified that the lung disease of "dusty trades" workers, silicosis(scarring of the lung tissue), and found that it was caused by the inhalation of "free" or crystallinesilica dust.

One of the most astounding incidents demonstrating the effects of inhaling large amounts ofcrystalline silica dust particles was during the Depression with the construction of a tunnelat Hawk's Nest, WV. 2,000 construction workers dug through a ridge of almost pure quartzwithout any respiratory protection. 400 men died at the site and 1,500 contracted acute silicosis.Another occurrence was in the early 1990's when over 100 acute and accelerated cases ofsilicosis occurred to Mexican sandblasters in Midland-Odessa, Texas.

During the 1980's, studies were conducted that suggested that crystalline silica was acarcinogen. In 1987, the International Agency for Research on Cancer (IARC), an agencyof the World Health Organization, evaluated the available medical literature on silica andconcluded that crystalline silica was a 2A substance, a probable carcinogen for humans.

Occupational exposure to the inhalation of crystalline silica particles over a lifetimepotentially not only causes silicosis, but also silocotuberculosis, enlargement of the heart,interference with the body's immune system (scleroderma) and when ingested, damage tothe kidneys. Studies of miners have revealed that silicosis typically does not occur untilafter the age of 50 and that the disease will progress after leaving the environment.

Because of its potential to cause health problems, a number of regulations and guidelines havebeen established for silica by various agencies.


The Occupational Safety and Health Administration's (OSHA) Hazard CommunicationStandard (HCS) requires that businesses that use materials containing 0.1% or morecrystalline silica must follow Federal guidelines concerning hazard communicationand worker training.

In 2002, OSHA established a National Emphasis Program (NEP) forCrystalline Silica exposure in an effort to reduce health hazards associated with occupationalexposures. First it recommends that manufacturers replace it with safer substances when possible.Next, it prescribes that when working with it the use of protective equipment such as respirators,and that the dust be controlled with proper exhaust ventilation, water sprays and to wearwashable or disposable clothing, vacuum the dust, or change into clean clothing before leavingthe work site, and to wash their hands and face to remove the dust. One can refer to OSHA'sSafety and Health Program Management Guidelines for their recommendations in detail.

In 1996, the EPA did an extensive study on "Ambient Levels and Non-Cancer Health Effectsof Inhaled Crystalline and Amorphous Silica" which states in its introduction that "(it) has longbeen recognized as a major occupational hazard, causing disability and deaths among workersin several industries" and then concludes with "deficiencies remaining in national surveillancesystems and the insensitivities of current diagnostic techniques still hamper efforts to determinethe prevalence of silicosis in the United States."

With that said one must be especially cautious in its use when children, asthmatics of any age,allergy sufferers, and the elderly are present. (Wikipedia)

Fiber Cement Board

In reviewing the Material Safety Data Sheet (MSDS ) for a Fiber Cement Board made by a wellknown manufacturer, I found that it was made up of the following.

  • Crystalline Silica (Quartz)
  • Calcium Silicate (Hydrate)
  • Calcium Carbonate
  • Calcium Aluminum Silicate (Hydrate)
  • Cellulose
  • Carbon Black
  • Other filler
  • Painted/sealed with water based acrylic.

Carbon Black was listed as a known carcinogen, and PEL's (prescribed exposure limits) werelisted for Calcium Carbonate as well. I looked into their respective MSDS's.

Both indicatethat inhalation might cause irritation, and one should wash exposed skin with soap and water,and wear protective glasses and clothing.