MSA altair 4 - Page 17

MSA DESCRIPTION
ALTAIR 4 - Operating Manual 17
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
= 35 ppm
10-minute exposure of 35 ppm and 5 minutes exposure of 15 ppm:
(10 minutes x 35 ppm) + (5 minutes x 5 ppm)
15 minutes
= 25 ppm
2.3.5 Time Weighted Average (TWA page)
WARNING
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 LEDs flash
• TWA icon flashes.
To reset the TWA:
(1) Access the TWA page.
(2) Press the
[ ]
button.
The TWA alarm is calculated over an eight-hour exposure.