Stel Calculation Examples; Time Weighted Average (Twa Page); To Reset The Twa Readings - MSA ALTAIR 4X Operating Manual

2. Press the ▲ button.
The STEL alarm is calculated over a 15-minute exposure.

STEL calculation examples:

Assume the instrument has been running for at least 15 minutes:
• 15-minute exposure of 35 ppm:
(15 minutes x 35 PPM)
15 minutes
• 10-minute exposure of 35 ppm and
5 minute-exposure of 15 ppm:
(10 minutes x 35 PPM) + (5 minutes x 15 PPM)
This page can be de-activated through MSA Link.

2.3.5 Time Weighted Average (TWA Page)

If the TWA alarm activates, leave the contaminated area
immediately; the ambient gas concentration has reached the
preset TWA alarm level. Failure to follow this warning will
cause over-exposure to toxic gases and persons relying on
this product for their safety could sustain serious personal
injury or death.
The TWA icon appears on the display to show the average exposure
since the instrument was turned ON or since the TWA reading was
reset. When the amount of gas detected is greater than the eight-hour
TWA limit:
• alarm sounds
• alarm lights flash
• TWA icon flashes.

To Reset the TWA Readings

1. Access the TWA Page.
2. Press the button.
▲
The TWA alarm is calculated over an eight-hour exposure.
= 35 PPM
15 minutes
" WARNING
= 25 PPM
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