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Chemical Safety

Nearly every type of chemical is safe to use when proper engineering and handling practices are observed. However, the engineering and other controls used for chemicals must be designed based upon the hazardous properties of the specific chemicals being used. The key to safe handling and use of chemicals is understanding the specific physical and health hazards associated with the chemicals in order to implement appropriate controls.

What Is A Hazardous Chemical?
A hazardous chemical is a material that has the ability to cause illness, injury or death due to a chemicals toxic nature and/or its physical characteristics.

What Are The Health Hazards Of A Chemical?

The health hazards associated with chemical exposures are attributed to statistically significant evidence that adverse health effects may occur in exposed employees. The chemical effect, on a living organism, is dose dependent. In some cases, the toxicological data is based on animal studies and extrapolated to humans. Hazardous chemicals may be carcinogenic, toxic or highly toxic agents, reproductive toxins, irritants and/or corrosives.

It is very important to look at the ways toxic chemicals are classified and how they produce their toxic effects. Toxic chemicals are classified by their physical state, chemical nature and biological activity. A toxic agents physical state and solubility as a gas, vapor or aerosol will determine how the chemical will enter the body and produce its effect. Irritant chemicals such as strong acids or alkalis may produce a localized effect when exposed to the skin or the irritant may also travel through the skin and attack the bone (hydrofluoric acid). Highly soluble materials such as ammonia, alkaline dusts and mists, hydrogen chloride and hydrogen fluoride will tend to affect the upper respiratory tract. Other materials with intermediate solubility such as halogens, ozone and phosphorus chloride affect both the upper respiratory tract and the pulmonary tissue. Insoluble materials such as nitrogen dioxide, phosgene or arsenic trichloride primarily affect the lung. There are some exceptions to these examples above where a material i.e., ethyl ether is absorbed into the blood stream from the alveoli without accumulating at that site. Finally, some chemicals are asphyxiants that deprive the body of oxygen. Simply asphyxiants such as nitrogen, nitrous oxide, carbon dioxide, hydrogen and helium are physiologically inert gases which in sufficient quantity exclude an adequate oxygen supply.

Routes of Exposure

Hazardous chemicals which are toxic to humans generally seek a target organ upon which the chemical will have an affect. The major target organs include the liver, kidneys, lungs, nervous system, eyes and skin. The primary routes of exposure, by importance, are by inhalation, skin and eye absorption (dermal and mucous), ingestion and injection. Inhalation exposure occurs when unprotected workers are accidentally exposed to fugitive emissions and the chemical produces its effect on the respiratory tract and/or the blood stream. Ingestion of a chemical occurs either by transfer of a chemical particulate from contaminated hands to food, cigarettes or by touching ones mouth. Exposure by injection occurs primarily from injection of experimental animals.

Health Effects And Individual Vulnerability

Health effects from exposure to hazardous chemicals can either be acute, chronic, localized or systemic. Individuals may respond differently to the same dose depending on their body size, rate of metabolism, general health and strength, age, sex and race. The terms "acute", "chronic", "local" and "systemic" are frequently used in toxicology and discussions about health effects of chemicals. These terms are defined below.

Acute effects occur over a very short period of time as a result of a high dose exposure (e.g. a release of a chlorine gas at a swimming pool).
Chronic effects occur over an extended period of time usually from a low dose exposure (e.g. exposure to asbestos or silica which results in asbestosis or silicosis).
Localized effects are generally the result of skin or eye contact with a chemical which results in a localized response such as skin or eye burning.
Systemic effects occur as a result of any of the above exposure routes, however, any of the target organs (the liver, kidneys, lungs, nervous system, eyes and skin) may be affected.

Chemical Toxicity
A variety of tests (inhalation, skin absorption or ingestion) can be performed to determine the degree of toxicity of a hazardous chemical and its toxic effect. The results of these toxicity tests are used to establish exposure limits for the individual and to provide a ranking of the degree of toxicity. An excellent source for toxicity information is the Material Safety Data Sheet (MSDS). Some commonly used criteria for defining the extent of toxicity are defined below:

Inhalation: LC50 (ppm or mg/m3) - This represents the air concentration to which one can be exposed which will cause death in 50% of the exposed population.
Absorption: Skin LD50 (mg/kg) ­ This represents the dosage (milligrams of chemical per kilogram of body weight) absorbed through the skin which will cause death in 50% of the population.
Ingestion: Oral LD50 (mg/kg) - This represents the dosage (milligrams of chemical ingested per kilogram of body weight) which will cause death in 50% of the exposed population.

Exposure Limits
Different types of exposure limits have been established to provide protection for workers and others exposed to chemicals. The two most commonly cited criteria are the following in the US:
      ACGIH-TLV

One exposure limit established by the American Conference of Governmental Industrial Hygienist (ACGIH) is the Threshold Limit Value (TLV). The TLV refers to the airborne concentrations of chemical substances under which it is believed that nearly all workers may be repeatedly exposed day after day without experiencing adverse health effects. Because of individual susceptibility, some workers may experience discomfort or aggravation of a pre-existing condition at or below the TLV.

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      OSHA-PEL

Permissible Exposure Limit (PEL) is the same as a TLV, but it is a legal limit established by Occupational Safety and Health Administration (OSHA). The PEL may be expressed as a time weighted-average (TWA), short-term exposure limit (STEL) or a ceiling (C) concentration. The TWA exposure is an actual exposure over a period of 8 hours. The TWA-STEL is similar to the TWA, but this is a maximum exposure for a 15 minute period. The TLV-C is the ceiling exposure limit which should not be exceeded at any time during any part of the work exposure. Immediately Dangerous to Life and Health (IDLH) is the concentration which should not be reached even instantaneously.

What Are The Physical Hazards Of A Chemical?
Chemicals can present one or more physical hazards including:

Corrosives - (Acids and Bases)
Flammables - (Liquids and Solids)
Oxidizers - (Support Combustion)
Pyrophoric Materials
Cryogenic Materials
Reactive Materials

Corrosives Chemicals Can:

Destroy human tissue
Give off dangerous fumes
Can dissolve and corrode material and equipment
Measured on the pH scale (hydrogen ion activity)

Flammables
Chemicals that are identified to be flammable are considered to have a Flashpoint and Explosive Limits. The Flashpoint is the lowest temperature at which a flammable liquid gives off enough vapor to form an ignitable mixture with air. The Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) limits are the minimum and maximum concentrations of a flammable gas or vapor (percent by volume in air) between which an explosion can occur if an ignition source is present.

Flammable chemicals have a Flashpoint less than 100ºF. Combustible chemicals have a Flashpoint greater than 100ºF and less than 200ºF.

Oxidizers
Oxidizers can initiate or promote combustion in other materials and it can do so in the absence of ambient air.
Pyrophoric Chemicals
Pyrophoric chemicals ignite on contact with air at temperatures below 140^oF producing extreme fire hazard. These types of fires may explode on contact with water or carbon dioxide extinguishers.

Cryogenic Materials
These gases, stored under pressure, become liquids below ­150^oF and present a freezing hazard while having the ability to expand significantly upon evaporation.

Reactive Materials
These are substances that can enter into a hazardous reaction with other stable or unstable materials resulting in:

Hazardous decomposition
Generation of heat
Hazardous by-products
Hazardous polymerization