Glossary of Terms

Term Definition
dB Decibel – a unit used to measure the relative power of sound. A 3db increase in sound output power represents a doubling of the perceptible volume.
LCD Liquid Crystal Display – an electronic visual display that uses the light modulating properties of liquid crystals.
LEL / LFL Lower Explosive Limit / Lower Flammable Limit – the minimum concentration at which a gas will explode. A common unit of measurement is a percent of the LEL.
PID PhotoIonization Detector – an instrument that utilises ultra-violet light energy to ionize and detect the presence of an unknown gas or vapor.
PPM Part Per Million – a common unit of measurement for toxic gases. This term literally means one part out of one million possible parts.
STEL Short Term Exposure Limit – the average amount of gas (in PPM) a worker can be exposed to in a 15 minute period with no long term health effects. For example, this may occur 4 times a shift with one hour between 15 minute exposures.
TWA Time Weighted Average – the average amount of gas (in PPM) a worker can be exposed to over a certain time period. This time is defined as 8 hours to represent a normal work day.
UEL/UFL Upper Explosive Limit/Upper Flammable Limit – the maximum concentration at which a gas will explode.
VAC Volts Alternating Current – an electric current that reverses direction at regular intervals.
VDC Volts Direct Current – an electric current of constant direction.
VOC Volatile Organic Compound – any compound containing carbon, except methane, that can be easily vaporized.