12 Asbestos Safety Manual Environmental Health and Safety D. Potential Health Effects Related to Asbestos Routes of Entry While asbestos fibers may gain entry into the body through ingestion, the major route of exposure is inhalation. Asbestos fibers have no odor, and those that you may inhale are invisible to the naked eye. The Respiratory System The respiratory system includes the mouth, nose, wind pipe (trachea), bronchi, and lungs. The lungs are located within the pleural cavity. Lying within the cavity and covering the lungs is a lining called the pleural mesothelium. The lungs contain air sacks called alveoli. The alveoli are the sites where oxygen is absorbed into the blood and carbon dioxide is removed from the blood. The body’s respiratory system has defense mechanisms to keep foreign particles from causing damage. Amazingly, estimates indicate that these mechanisms are 95 to 98 percent effective. Examples of some defense mechanisms and their functions are: • The mouth and nose filter out very large particles. • Coated bronchi filter out smaller particles. • Cilia, which are hair-like protrusions on cells lining the airways (bronchial tree), move particles up to the back of the mouth where they are swallowed or expelled. • Alveoli in the lower respiratory system trap the smallest particles. The particles may be attacked by large cells, known as macrophages, which try to digest them. Because asbestos is a mineral fiber, the macrophages are often not successful. Asbestos Health Risks Most of the information about asbestos disease comes from studying workers in the various asbestos industries. The bulk of data comes from World War II shipbuilding activities and the asbestos industries in the United States and England. Exposure to very high levels of airborne asbestos typical of asbestos trades prior to 1972 has been linked with the following diseases: Asbestosis is a chronic disease in which the lungs become scarred (fibrosis) as a result of a biological reaction to the inhalation of asbestos fibers. Scarring causes thickening of the walls of the lungs and a reduction in the capacity to transfer oxygen to the bloodstream. Asbestosis results after exposure to high concentrations of fibers over a long period of time. Symptoms usually occur 15 to 30 years after the first exposure.