Toolbox Topic: Concrete and Crystalline Silica
Concrete and crystalline silica can be very dangerous when airborne. In this episode, we will talk about the dangers of crystalline silica and the precautions you should take when working around it.
Definitions
According to OSHA: Crystalline silica is a common mineral found in construction materials such as sand, stone, concrete, brick, and mortar. It is covered in the various OSHA standards, including 1910,1926, and 1915.
Crystalline silica is a naturally occurring mineral in the earth’s crust. You will find it in sand, stone, and concrete materials. It can be hazardous if inhaled in excessive quantities.
History of Concrete and Crystalline Silica
The invention of “concrete” depends on how you define it. In ancient times a version of concrete was made from crushed or burnt gypsum or limestone. Adding sand and water created mortar which acted like a plaster to hold stones together.
Concrete in its Earliest Forms
The Nabataea traders controlled a small empire in the regions of southern Syria and northern Jordan around 6500 BC. They built some of the first concrete-like structures. Somewhere along the way, they even discovered the advantages of hydraulic lime, a type of cement that hardens underwater. Later, they developed kilns to produce mortar for house construction, concrete floors, and underground waterproof cisterns. These cisterns were kept secret and one of the reasons the Nabataea could survive so well in the desert.
In 1300 BC, builders in the Middle East discovered cement. Clay walls were coated with burned limestone. This combination created a chemical reaction to form a protective surface that hardened.
Egypt
Fast forward to 3000 BC, and the ancient Egyptians used straw mixed with mud to make bricks. They would use gypsum and lime mortars in building the pyramids. One of the pyramids required about 500,000 tons of mortar.
China
During the same period, the Chinese used a form of cement in building the Great Wall. A key ingredient in the mortar used was glutenous, sticky rice. Many of the structures created with this type of mortar are still standing today!
The Romans
By 200 BC, the Romans were skilled in their use of concrete. Still, it was very different from the concrete we use today. Most of their structures were built by stacking stones of various sizes. They would then hand-fill the spaces with mortar. Although they had developed bricks, they added little or no structural value. Their use was mainly cosmetic.
Rome would use more advanced materials for their art and land-based infrastructure. They produced cement from naturally reactive volcanic sand.
The Romans built the Pantheon, the Colosseum, and Roman Baths, using this type of cement. The construction of the Pantheon is remarkable. It has a dome that is 142 feet in diameter. At its peak, it has a 27-foot hole, called an oculus, which is 142 feet above the floor. It is the largest un-reinforced concrete dome ever built.
They also used this type of cement for structures such as docks, bridges, storm drains, and aqueducts. The fascinating thing is that the volcanic sand reacts chemically with lime and water to solidify and hydrate into a waterproof rock-like mass. This likely represents the first large-scale use of a genuinely cementitious binding agent.
Modern Times
From then to today, cement has improved and evolved into what we know as modern concrete. Modern concrete is made of Portland cement which includes coarse and fine aggregates of stone and sand mixed with water.
The First Signs of Danger
In 1700 Silicosis was first discovered by Dr. Bernardino Ramazzini. Silicosis is a condition that affects the lungs. Stone cutters began showing symptoms after working with dust containing crystalline Silica.
In 1900, Dr. Alice Hamilton documented silica-related illnesses among granite workers.
Around the same time, granite cutters in Vermont recognized a connection between silica dust and the resulting illnesses. In the 1930s, they successfully negotiated for the installation of ventilation equipment.
As the risk of silica dust has become widely recognized, so have the precautions taken to protect against its dangers. As we will see in the statistics section, the statistics have improved dramatically over the years. Even so, it is up to all of us to remain committed to taking the necessary precautions when working around silica dust.
Concrete and Crystalline Silica Statistics
Exposure to silica dust occurs in many industries. Some of the heavy industries include mining, quarrying, sandblasting, rock drilling, road construction, and tunneling operations. Other less hazardous industries include pottery making, stone masonry, and concrete repair.
OSHA estimates that two million construction workers are exposed to crystalline silica. This exposure affects over 600,000 workplaces.
From 2001–2010, a total of 1,437 people had silicosis as an underlying or contributing cause of death.
The number of deaths from silicosis declined from 1,065 in 1968 to 165 in 2004. It continued to decrease to 101 deaths by 2010.
Concrete and Crystalline Silica Safety Tips
Safety Tip#1 Know the Dangers
Silica dust particles become trapped in lung tissue and cause inflammation and scarring. The particles also reduce the lungs’ ability to take in oxygen. This condition is called silicosis. Silicosis results in permanent lung damage and is progressive, debilitating, and sometimes fatal.
As of today, there is no effective treatment for silicosis. Chronic silicosis can develop or progress even after occupational exposure has ceased. Victims receive supportive care and may be eligible for a lung transplant.
Other illnesses that can develop when exposed to high levels of silica dust include:
- lung cancer
- chronic obstructive pulmonary disease (COPD)
- Kidney disease.
Tip#2 Eliminate or Substitute
Eliminating the hazard or substituting less hazardous material or processes is always preferable. When possible, use other substances for abrasive blasting materials with less or no crystalline silica.
Tip#3 Controlling the Exposure
Use water and vacuums at the source to reduce or eliminate the dust before it becomes airborne. Use ventilation systems to remove the dust from the air. Also, maintain these systems to keep them operating.
If controls don’t eliminate the hazard or are insufficient, use PPE. PPE should include respirators, eye protection, aprons, footwear, and gloves. Be sure you follow whatever the requirements are for your specific location.
Tip#4 Remove the Dust Safely
- Do not blow or brush the dust off your clothes or take it home with you
- Wear washable or disposable work clothes
- Shower in facilities where available
- Change into clean clothes before leaving your work site
Tip#5 Personal Hygiene
Wash your hands and face before taking a break and after your shift. Also, avoid eating or drinking in dusty areas. Lastly, don’t smoke in these areas either.
Sources
https://www.osha.gov/sites/default/files/publications/OSHA3681.pdf
https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1053
https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.1153
https://www.osha.gov/laws-regs/regulations/standardnumber/1915/1915.1053
https://www.cdc.gov/niosh/topics/silica/risks.html
https://www.corrosionpedia.com/definition/3183/crystalline-silica
https://www.silica-safe.org/regulations-and-requirements/status-of-regulatory-efforts/history
https://www.nachi.org/history-of-concrete.htm
https://www.osha.gov/sites/default/files/publications/osha3681.pdf