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
Jamaica Plain, MA

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.


Cynthia Phakos

Answered by Cynthia Phakos

Los Angeles, CA

Koffka Phakos Design

April 30, 2012

As a contractor that is installing this everyday you would be well advised to follow all of the guidelines 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 irritates them, reducing lung capacities.

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

Children, asthmatics of any age, allergy sufferers, and the elderly (all of whom have reduced lung capacity) 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 a non-crystalline and crystalline state. Plentiful on all continents, the most prevalent source is 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 primary use is in making glass which dates back 5,000 years but was also used in pottery, cement and other materials where sand is added.

Today, the glass industry uses a highly, refined crystalline 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 several construction products including Gypsum Board, Joint Compound, and Fireproofing to name a few.

Health Issues

With the Industrial Revolution and the invention of the pneumatic hammer in 1897, higher levels of dust exposure caused severe respiratory diseases, shortening the lives of workers. In 1915, the British 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 crystalline silica dust.

One of the most astounding incidents demonstrating the effects of inhaling large amounts of crystalline silica dust particles was during the Depression with the construction of a tunnel at Hawk’s Nest, WV. 2,000 construction workers dug through a ridge of almost pure quartz without 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 of silicosis occurred to Mexican sandblasters in Midland-Odessa, Texas.

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

Occupational exposure to the inhalation of crystalline silica particles over a lifetime potentially not only causes silicosis, but also silocotuberculosis, enlargement of the heart, interference with the body’s immune system (scleroderma) and when ingested, damage to the kidneys. Studies of miners have revealed that silicosis typically does not occur until after 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 have been established for silica by various agencies.


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

In 2002, OSHA established a National Emphasis Program (NEP) for Crystalline Silica exposure in an effort to reduce health hazards associated with occupational exposures. 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 wear washable or disposable clothing, vacuum the dust, or change into clean clothing before leaving the work site, and to wash their hands and face to remove the dust. One can refer to OSHA’s Safety 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 Effects of Inhaled Crystalline and Amorphous Silica” which states in its introduction that “(it) has long been recognized as a major occupational hazard, causing disability and deaths among workers in several industries” and then concludes with “deficiencies remaining in national surveillance systems and the insensitivities of current diagnostic techniques still hamper efforts to determine the 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 well known 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) were listed for Calcium Carbonate as well. I looked into their respective MSDS’s.

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

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