Operation; Environmental Factors - MSA ALTAIR 4 Operating Manual

OPERATION

3 Operation
Instrument operation is dialog driven from the display with the aid of the
three Function buttons (see Section 2).
3.1

Environmental Factors

A number of environmental factors may effect the gas sensor readings,
including changes in pressure, humidity and temperature. Pressure and
humidity changes affect the amount of oxygen actually present in the
atmosphere.
Pressure Changes
If pressure changes rapidly (e.g., stepping through airlock), the oxygen
sensor reading may temporarily shift and possibly cause the detector to
alarm. While the percentage of oxygen may remain at or near 20.8 vol%,
the total amount of oxygen present in the atmosphere available for
respiration may become a hazard if the overall pressure is reduced by a
significant degree.
Humidity Changes
If humidity changes by any significant degree (e.g., going from a dry, air
conditioned environment to outdoor, moisture laden air), oxygen readings
can be reduced by up to 0.5 %, due to water vapor in the air displacing
oxygen.
The oxygen sensor has a special filter to reduce the effects of humidity
changes on oxygen readings. This effect will not be noticed immediately,
but slowly impacts oxygen readings over several hours.
Temperature Changes
The oxygen sensor has built-in temperature compensation. However, if
temperature shifts dramatically, the oxygen sensor reading may shift. Zero
the instrument at a temperature within 86 °F (30 °C) of the work site
temperature for the least effect.
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ALTAIR 4 - Operating Manual
MSA