A hazardous chemical is one that can cause physical harm to you or that can have a negative effect on your health if you are exposed to the chemical. The following terms are often used to describe the health hazards of chemicals:

• Corrosives - can seriously damage the skin upon contact, mucous membranes and lungs if inhaled, or the gastrointestinal tract and stomach if ingested.
• Irritants - can cause inflammation of tissue at point of contact, including bronchitis or other lung damage if inhaled.
• Asphyxiants - deprive the body of oxygen. Simple and chemical asphyxiants render the body incapable of maintaining an adequate oxygen supply. Chemical asphyxiants are active at very low concentrations.
• Primary Anesthetics - depress the central nervous system.
• Hepatotoxins - cause damage to the liver.
• Nephrotoxins - cause damage to the kidneys.
• Neurotoxins - cause damage to the nervous system. The nervous system is especially sensitive to organ metallic compounds and certain sulfide compounds.
• Hemotoxins - cause damage to blood cells or bone marrow.
• Carcinogens - are commonly described as any agent that can initiate or speed the development of malignant or potentially malignant tumors, malignant neoplastic proliferation of cells, or cells that possess such material.
• Reproductive Toxins - are chemicals that affect the ability to have children.
• Mutagens - induce chromosome changes that may become hereditary.
• Teratogens - cause birth defects in developing fetuses but effects are not hereditary.
• Sensitizers - cause allergic reactions after repeated exposures. The reaction may be as mild as a rash (contact dermatitis) or as serious as anaphylactic shock.
• Toxic Chemicals- are poisonous in moderate amounts.
• Acutely Toxic Chemicals - are poisonous in very small amounts.
• Cyanide and Sulfur Compounds - can release toxic gasses that affect the ability of the body to transport oxygen.
• Radioactive Isotopes - emit ionizing radiation, which can cause direct tissue destruction or interact with cellular nucleic material.

There are four basic ways to be exposed to hazardous chemicals: inhalation; skin contact and absorption; ingestion; and injection. Understanding these routes of exposure can aid you in taking actions to prevent exposure.

• Inhalation of vapors, gases, mists, or particulates can result in negative health effects. Once inhaled, chemicals can cause damage through direct contact with respiratory tract tissue, with health effects ranging from simple irritation to severe tissue destruction. Inhaled substances can also be absorbed into the blood, circulated through the body with uptake occurring in organs that have an affinity for the chemical. Health effects can then occur in the organs that are sensitive to the toxicant.
• Skin (dermal) contact can cause effects that are relatively mild, such as redness, or more severe effects, such as destruction of skin tissue. Many chemicals can be absorbed into the blood system through the skin. Once absorbed, they may cause damage to internal organs. Rashes, cuts, and abrasions on the skin increase the potential for chemicals to enter the body upon contact. The eyes are particularly sensitive to chemicals. Even a short exposure can cause severe effects to the eyes or the substance can be absorbed through the eyes and transported to other parts of the body causing harmful effects.
• Ingested chemicals do not generally harm the gastrointestinal tract itself unless the chemicals are irritating or corrosive. Chemicals that are soluble are absorbed through the lining of the gastrointestinal tract. They are then transported by the blood to internal organs where they can cause damage.
• Injection of substances can happen if the skin is penetrated or punctured by contaminated objects. Effects can then occur as the substance is circulated in the blood and deposited in the organs.

The following terms are often used to describe the physical hazards of chemicals:

• Flammable and Combustible Liquids - are materials which, under standard laboratory conditions, can generate sufficient vapors to cause a fire in the presence of an ignition source. Materials which generate sufficient vapors to ignite at temperatures below 100° F [38° C] are "flammables," whereas materials that require temperatures above 100° F to provide sufficient vapors for ignition are "combustibles." Flammable liquids are classed as 1A, 1B, or 1C, with 1A being the most flammable. Depending on density, vapor trails can rise, sink, or traverse horizontally to reach an ignition source, resulting in a flashback fire. Fire can also result from reactions between flammables or combustibles and oxidizers.
• Corrosives - are materials that corrode metal and generally present a storage hazard as well as health hazards.
• Reactives - are chemicals that can release energy quickly and forcefully, depending on various environmental conditions. In some cases the release of energy may result in a detonation.
• Oxidizers - are fire and explosion hazards when in contact with organic material or strong reducing agents.
• Water Reactives - react with water to form heat and flammable or explosive gases.
• Pyrophorics - ignite spontaneously in air
• Peroxide-forming Chemicals and Organic Peroxides - are among the most hazardous substances handled in chemical use areas. They are generally low-power explosives that are sensitive to shock, sparks, or other accidental ignition. Organic Peroxides have a 0-0 bond that makes them unstable. Some other organic compounds can form peroxides when exposed to air and light.
• Compressed Gases in Cylinders - pose special hazards because of the ability of gas to quickly and widely disperse when released.
• Cryogens - are supercooled liquids that can damage body tissue.