Crowcon T4 - Short Term Exposure Limit Alarm (STEL)

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2.3.3 Short term exposure limit alarm (STEL)
For each toxic gas being monitored T4 stores information about the gas levels detected to determine
the average exposure over a 15 minute running period. If the average levels detected over the dened
period of time exceed predetermined levels, T4 will go into alarm (STEL is not monitored for the
duration of a bump test or calibration). The STEL alarm level can be congured via Portables Pro 2.0.
In the alarm state, the STEL symbol on the screen
will ash indicating the STEL levels have
been exceeded, the sounder will emit a tone, alarm LEDs will ash red and blue, and the T4 will
vibrate.
i
If +ve Safety™ is congured the +ve Safety™ LED will also be illuminated red. The LED
will return to green when the STEL alarm is cleared.
2.3.4 Time weighted average alarm (TWA)
For each toxic gas being monitored T4 stores information about the gas levels detected to determine
the average exposure over an 8 hr running period. If the average levels detected over the dened
period of time exceed predetermined levels, T4 will go into alarm (TWA is not monitored for the
duration of a bump test or calibration). The TWA alarm level can be congured via Portables Pro 2.0.
In the alarm state, the TWA symbol on the screen
will ash indicating the TWA levels have been
exceeded, the sounder will emit a tone, alarm LEDs will ash red and blue, and T4 will vibrate.
i
If +ve Safety™ is congured the +ve Safety™ LED will also be illuminated red. The LED
will return to green when the TWA alarm is cleared.
2.3.5 TWA Resume function*
TWA Resume allows TWA, STEL and peak readings to be retained after T4 has been switched off
for a period of time, for example while an operator travels to a new location. This prevents recent
toxic exposure history from being lost and the associated risk of the operator exceeding safe
exposure levels.
If T4 is switched off for less than 15 minutes and the TWA Resume function is selected (see below),
T4 will retain the STEL, TWA and peak gas values when powered back on.
If T4 is switched off for more than 15 minutes but less than 8hrs, and the TWA Resume function is
selected (see below), T4 will retain the TWA and peak gas values when powered back on but the
STEL values will be cleared.
If T4 is switched off for more than 8hrs the TWA Resume function will not be available in the start up
sequence and T4 will clear the TWA, STEL and peak gas values when powered back on.
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