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The STEL (Short Term Exposure Level) function measures the level of toxic
gas during a fifteen (15) minute interval and alarms when the preset STEL
value in parts per million is exceeded. The alarm levels are as follows:
STEL TWA
Ammonia 35 ppm 25 ppm
Carbon monoxide 100 ppm 25 ppm
Chlorine 1 ppm 0.5 ppm
Chlorine Dioxide 0.3 ppm 0.1 ppm
Hydrogen Cyanide 4.0 ppm 2.0 ppm
Hydrogen sulfide 15 ppm 10 ppm
Nitrogen Dioxide 5.0 ppm 3.0 ppm
Phosphine 1 ppm 0.3 ppm
Suphur Dioxide 5 ppm 2 ppm
To enter the TWA/STEL Menu, depress the “SELECT” pushbutton as de-
scribed in Section 6.2 when the TWA/STEL Menu screen is displayed. The
instrument will display one of the following screens:
<gas> TWA/STEL MENU
For Toxic Gases STEL = 0 ppm
TWA = 0 ppm @ 0:05
RESET SHOW
DISABLE TWA/STEL
STEL and TWA values are calculated. STEL averages exposure for the
latest fifteen (15) minutes. TWA shows the eight-hour average exposure.
Both measures start from zero when the instrument is turned on. The TWA
reading accumulates total exposure since turn-on or “RESET” and is calcu-
lated as if the total exposure occurred in a standard eight-hour shift.
The “RESET/DISABLE” pushbuttons allows the user to reset the values and
time on the display to “0”. One of following screens will be displayed when
the “RESET/DISABLE” pushbuttons are depressed:
<gas> TWA/STEL MENU
TIME AVERAGE VALUES
For Toxic Gases
RESET DISABLE