Basic Air
Monitoring
Concepts
And Use Of
The Altair 4
Gas Meter
MSA Altair 4
Multi-Gas Meter
Explosive Atmosphere
Oxygen Concentration
Carbon Monoxide
Hydrogen Sulfide
Photo Ionization Detector
Meter using ultraviolet light to
detect vapors with low LEL’s,
up to 10,000 ppm
Colorimetric Tubes
Flame Ionization Detector
Similar to the
PID, but uses a
hydrogen flame
instead of UV
light to detect
vapors
Used to detect single
gases
Some Common Haz-Mat Terms
Vapor Pressure
The amount of force applied on a container by the vapors
coming from a substance. A vapor pressure greater than 40
mmHg is considered a respiratory hazard. Water has a VP
of inbetween 17 - 25 mmHg.
Vapor Density
The relative comparison of a material to air. This
determines whether the vapors will rise or settle. Air is
given a score of 1. If the density is less than one, say .8, the
substance will rise. If its say 1.9, the substance will settle.
The Metering Process
o Identification of the substance
o Placards
o MSDS Sheets
o DOT ERG guide (Orange Book)
o NIOSH Book
o Shipping Papers
o History of event
Getting Started
After turning the meter on in a clean atmosphere.
1. Determine flammability/explosive potential
2. What is the flammable range of the substance
you are metering ?
3. This number is usually given as a percentage.
4. What does this number mean ?
Flammable Range
Lower Explosive Limit (LEL)
The smallest concentration in air of a substance that will
support fire or an explosion
Upper Explosive Limit (UEL)
The largest concentration of a substance that will support fire
or an explosion
Example: Methane LEL = 5 % UEL 15 %
Methane
0%
5%
15 %
100 %
Correction Factors
LEL sensors are calibrated to a certain gas, in our case
pentane. The catalytic bead LEL sensor will respond to other
gases as if they are pentane. So what do we do if we are
metering something other than pentane ?
We use correction factors ! Yeah !
What are the correction factors for our meter ?
Methane 0.5
Hydrogen 0.5
Propane 0.8
Pentane 1.0
Take your explosive reading and multiply by
the numbers on the left to get your reading.
If your meter shows 25 % of the LEL and you
are monitoring methane, multiply 25 x 0.5, so
the actual reading is 12.5 %
Oxygen
Before entering the atmosphere to be metered, the oxygen
concentration should be in the normal range, approximately
20.8 %. Concentrations above 20.8 % and below 19.5 % should
be considered dangerous and the area left as soon as possible.
Calibration Vs. Bump Test
Calibration
Putting the meter into a ‘calibration mode’ and making sure
the meter reads within a specific range of a known gas and if
not, making necessary adjustments to correct.
Bump Test
Attaching the meter to a known source of gas and making
sure the meter alarms with the appropriate numbers.
Altair 4 Operation
Safe LED
The instrument is equipped with a green
"SAFE LED". This green SAFE
LED flashes every 15 seconds under the
following conditions:
• the SAFE LED feature is enabled
• instrument is in Measurement Mode
(Normal Operation)
• combustible reading is 0% LEL or
0.00%CH4
• Oxygen (O2) reading is 20.8%
• Carbon Monoxide (CO) reading is 0 ppm
• Hydrogen Sulfide (H2S) reading is 0 ppm
or 0 mg/m³
• no gas alarms are present (low or high)
• instrument is not in Low Battery warning
or alarm
• CO, H2S, STEL and TWA readings are 0
ppm or 0 mg/m³.
The √ symbol will be displayed in the Measure mode for 24
hours after a
successful Bump Test or calibration.
Instrument run
time 16 hours at 77°F (25 °C)
Charging time
≤ 4 hours
The maximum safe area charging voltage
Um = 6.7 Volts D.C.
Temperature
range
-4 °F to122 °F (-20 °C to 50 °C) operating
50 °F to 95 °F (10 °C to 35 °C) while
charging battery
A combustible gas reading
of "XXX” indicates the
atmosphere is above
100 % LEL or 5.00 % vol
CH4, and an explosion
hazard exists.
Move away from hazardous
area immediately.
Do not use the ALTAIR 4 Multigas Detector to test for combustible or
toxic gases in the following atmospheres as this may result in erroneous
readings:
• Oxygen-deficient or oxygen-rich atmospheres
• Reducing atmospheres
• Furnace stacks
• Inert environments
• Atmospheres containing combustible airborne mists/dusts.
• Do not use the ALTAIR 4 Multigas Detector to test for combustible
gases in atmospheres containing vapors from liquids with a high flash
point (above 38 °C, 100°F) as this may result in erroneously low
readings.