Environmental Health and Safety

MSDS Glossary

Pathologic
Pertaining to or caused by disease.
Pathology
Scientific study of alterations produced by disease.
PEL
Permissible Exposure Limit is an occupational exposure limit established by OSHA's regulatory authority. It may be a time-weighted average (TWA) limit or a maximum concentration exposure limit.
Percent Volatile
Percent volatile by volume is the percentage of a liquid or solid (by volume) that will evaporate at a temperature of 70°F. Examples: butane, gasoline, and paint thinner (mineral spirits) are 100 percent volatile; their individual evaporation rates vary, but in time, each will evaporate completely.
pH
The symbol relating the hydrogen ion (H+) concentration to that of a given standard solution. A pH of 7 is neutral. Numbers increasing from 7 to 14 indicate greater alkalinity. Numbers decreasing from 7 to 0 indicate greater acidity.
Physical Hazard
Used to describe a chemical that is explosive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable, or water reactive.
Placenta
A structure attached to the wall of the uterus to nourish the fetus during pregnancy.
Polymerization
A chemical reaction in which one or more small molecules combine to form larger molecules. A hazardous polymerization is such a reaction that takes place at a rate that releases large amounts of energy. If hazardous polymerization can occur with a given material, the MSDS usually will list conditions that could start the reaction and, if the material contains a polymerization inhibitor, the length of time during which the inhibitor will be effective.
ppb
Parts per billion. The concentration of a particular chemical in solution. For every one part of the chemical. there are a billion parts of solution. Used to express very low concentrations.
ppm
Parts per million. The concentration of a particular chemical in solution. For every one part of the chemical, there are a million parts of solution. Used to express very low concentrations. One inch in sixteen miles is a common example of the magnitude of parts per million.
Prenatal
Preceding birth.
psi
Pounds per square inch is the pressure a material exerts on the walls of a confining vessel or enclosure. For technical accuracy, pressure must be expressed as psig (pounds per square inch gauge) or psia (pounds per square inch absolute; that is, gauge pressure plus sea level atmospheric pressure, or psig plus approximately 14.7 pounds per square inch). See also mmHg.
Pulmonary
Relating to, or associated with, the lungs.
Pulmonary Edema
Fluid in the lungs.
Pyrophoric
A chemical substance that will ignite spontaneously in air at or below a temperature of 130°F (54.4°C).

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