Glossary of Terms
EVM Series User Manual
The highest level of toxic gas or oxygen reached while the unit is on.
PEL (Permissible
Exposure Limit)
Permissible exposure limit. PEL's are a regulatory limitation to exposure used to
specify the allowable exposure to a substance in the workplace and assume that the
exposure takes place over an 8-hour shift in a 40-hour work week. Note that there
are more stringent exposure limits for higher levels of exposure that may occur over
a shorter time interval.
There are three types of PELs:
Most permissible exposure limits are based upon an 8-hour time
weighted average (TWA). The air concentration may sometimes go
above the TWA value, as long as the 8-hour average stays below.
(NOTE: This measurement is not applicable with temperature.
relative humidity, or air velocity sensors.)
The maximum allowable concentration of a chemical that an
employee may be exposed to. It must never be exceeded, even for
an instant.
The Short Term Exposure Limit (STEL) is the maximum
concentration above the time-weighted average that employees can
be exposed to over a specific time period (usually 15 minutes) no
more than four (4) times per day. This stands for Short Term
Exposure Limit and is the maximum average concentration of a
toxic gas to which an unprotected worker may be exposed over any
fifteen-minute interval during a work period. The EVM calculates the
STEL by compiling fifteen one-minute averages, and updates that
average each minute after the initial fifteen-minute exposure. If the
STEL is reached or exceeded, the alarm activates, and the STEL
enunciator turns on.
Different regulatory agencies have different acronyms for PELs:
NIOSH (National Institute for Occupational Safety and Health) uses
REL (Recommended Exposure Limit), and ACGIH (American
Conference of Governmental Industrial Hygienists) uses TLV
(Threshold Limit Value).
(NOTE: This measurement is not applicable with temperature.
relative humidity, or air velocity sensors.)
A type of photodetector that is able to convert light source into either current or
voltage. With the EVM, it is used to measure the amount of light scattered from a
particle cloud.
Parts per million (or parts per billion) of concentration of the gas of interest in air. For
example, 1 ppm signifies one part of gas to 1 million parts of air.
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