Risk Analysis Glossary: S - U

Safety

1. Relative protection from adverse consequences.

Salinity

1. The concentration of salts in water.

Significant deterioration

1. Refers to pollution from a new source in previously "clean" areas. Congress has established standards for certain pollutants to prevent significant deterioration from existing conditions thus establishing increments which cannot be exceeded.

Sink

1. A place where pollutants are collected by means of processes such as absorption. The opposite of source.

Smoke

1. The visible aerosol that results from incomplete combustion.

SMR

1. Standardized mortality ratio.

SO₂

1. Sulfur dioxide.

Solid waste

1. Useless, unwanted, or discarded material with insufficient liquid to be free-flowing.

Solid waste disposal

1. The final placement of refuse than cannot be salvaged or recycled.

Somatic

1. Pertaining to or characteristic of the body.
2. When modifying "cells", it refers to those that are not germ cells capable of passing along a mutation to progeny. [S. L. Brown]

Source

1. A place where pollutants are emitted, for example a chimney stack.

Source term

1. The release rate of hazardous agent from a facility or activity.

Stack effect

1. Used in reference to air, as in a chimney, that moves upward because it is warmer than the surrounding atmosphere.

Stack emissions

1. Effluents released into the atmosphere from the exhaust flue of a building; usually refers to pollutants but can refer to steam or other nonpolluting effluents.

Standard deviation

1. A measure of dispersion or variation, usually taken as the square root of the variance.

Standard geometric deviation

1. Measure of dispersion of values about a geometric mean; the portion of the frequency distribution that is one standard geometric deviation to either side of the geometric mean; accounts for 68% of the total samples.

Standardized mortality ratio (SMR)

1. The ratio of observed deaths in a population to the expected number of deaths as derived from rates in a standard population with adjustment of age and possibly other factors such as sex or race.

Standard normal deviation

1. Measure of dispersion of values about a mean value; the positive square root of the average of the squares of the individual deviations from the mean.

Stationary source

1. A pollution location that is fixed rather than moving.

Statistical significance

1. The statistical significance determined by using appropriate standard techniques of statistical analysis with results interpreted at the stated confidence level and based on data relating species which are present in sufficient numbers at control areas to permit a valid statistical comparison with the areas being tested.

Steady state exposure

1. Exposure to an environmental pollutant whose concentration remains constant for a period of time.

Sulfate

1. A compound in which the hydrogen of sulfuric acid is replaced by either metal or by an organic radical, to become a sulfate salt or sulfate ester respectively.

Sulfur dioxide (SO₂)

1. A heavy, pungent, colorless gas formed primarily by the combustion of fossil fuels. This major air pollutant is unhealthy for plants, animals, and people.

Surface water

1. All bodies of water on the surface of the earth.

Surrogate

1. Something that serves as a substitute. In risk analysis, surrogates are often used when data on the item of interest (a chemical, an industry, an exposure, etc.) is lacking. As an example, underground mining of coal and hardrock minerals can be used as a surrogate for underground oil shale mining.

Synergetic

1. Working together; an agent that works synergistically with one or more other agents.

Synergism

1. An interaction between two substances that results in a greater effect than both of the substances could have had acting independently.

Synergistic effects

1. Joint effects of two or more agents, such as drugs that increase each other's effectiveness when taken together.

Systematic error

1. A reproducible inaccuracy introduced by faulty equipment, calibration, or technique.

Temperature inversion

1. Layer of air in which temperature increases with altitude; very little turbulent exchange occurs within it.

Layer of air in which temperature increases with altitude; very little turbulent exchange occurs within it.

Temporary total disability

1. An injury which does not result in death or permanent disability, but which renders the injured person unable to perform regular duties on one or more full calendar days after the day of the injury.

Teratogenic

1. Substances that are suspected of causing malformations or serious deviations from the normal type, which can not be inherited in or on animal embryos or fetuses.

Teratology

1. Science that deals with abnormal development of the fetus and congenital malformation.

Threshold

1. A pollutant concentration [or dose] below which no deleterious effect occurs.

Threshold dose

1. The minimum application of a given substance required to produce an observable effect.

Threshold limit value (TLV)

1. Refers to airborne concentrations of substances and represents conditions under which it is believed that nearly all workers are protected while repeatedly exposed for an 8-hr day, 5 days a week (expressed as parts per million (ppm) for gases and vapors and as milligrams per cubic meter (mg/m³) for fumes, mists, and dusts).

Topography

1. The detailed delineation of the geographic features of a locality.

Total suspended particulate matter (TSP)

1. The total concentration of all airborne particles at a particular point in space.

Toxicant

1. A substance that kills or injures an organism through chemical or physical action or by altering the organism's environment; for example, cyanides, phenols, pesticides, or heavy metals; especially used for insect control.

Toxicity

1. The degree of danger posed by a substance to animal or plant life.

Toxicology

1. The study of the adverse effects of chemicals on living organisms.

Toxic substance

1. A chemical or mixture that may present an unreasonable risk of injury to health or the environment.

Toxic wastes

1. Wastes that contain substances in sufficient quantity to impinge harmfully on biological systems.

Trace

1. A very small amount of a material. Usually used in reference to concentrations which are on the order of or less than 1-10 parts per million.

Trace metals

1. Metals normally found in trace amounts due to their insolubility or to their relative lack of abundance in the crust of the earth.

Tumor

1. Any abnormal mass of cells resulting from excessive cellular multiplication.

Uncertainty analysis

1. A detailed examination of the systematic and random errors of a measurement or estimate; an analytical process to provide information regarding the uncertainty.

Upwind

1. Toward the direction from which the wind is blowing: counter to the wind.