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A general guide on the adverse effects of CO at various concentrations is given in Table
3. A concentration above 35 ppm in breathable air is cause for concern. The time-weighted limit
(8 hr.) for CO in the workplace is 50 ppm and the short-term (15 min.) limit is 200 ppm. The
effect of higher concentrations becomes more severe with increasing exposure time.
concentration above 200 ppm may be life-threatening, if exposure is long enough.
Concentration
50 ppm
200 ppm
400 ppm
800 ppm
1,600 ppm
3,200 ppm
6,400 ppm
The electrochemical cell used for CO measurements will respond to other substances that
are oxidized by the cell (see Section 5). Measurements of CO in ambient air can be made more
specific to CO by using the filter and probe provided for flue-gas measurements (see below).
The filter removes most, but not all, easily oxidizable vapors including some given off by
common household chemicals.
Flue Gases. To carry out flue gas measurements, select the PPM CO display, connect the
flue gas probe with its attached filter, and after warmup, insert the probe into the flue to read the
CO concentration in ppm. The standard flue gas probe is intended for flue gas checks which last
a minute or two. Longer sampling times may lead to a display of "bloc" as water condenses in
the probe, filter, or hose and blocks the gas intake to the instrument. If checks for CO in flue gas
are needed over longer periods use an Extended Duty Flue Gas Probe and Filter (see
Accessories). These probes have larger heat sinks and contain a water-removing substance in
their filters extending sampling times up to about half-an-hour.
If flue gas measurements are to be made on a regular basis, the alarm for the CO display
may be turned OFF (See Section 11) if the flue gas is expected to contain over 200 PPM CO.
CAUTION:
When measuring CO in flue gas, the filter provided with the probe must be used
to avoid interference from nitrogen oxides. A filter is good for at least three
months of ordinary use. It should be replaced or refilled when about 90% of its
purple materials has changed color to brown, or when it gets clogged or flooded
(see Accessories and Spare Parts).
WARNING:
Do not touch the flue probe immediately after a measurement. Running
the instrument for a short time in ambient air helps cool the probe quickly
and also removes condensed water.
Table 3. Effects of Carbon Monoxide
Inhalation Time and Symptoms
Time-weighted (8 hr.) limit in the workplace
Short-term (15 min.) limit in the workplace
Headache in 1-2 hrs., life threatening after 3 hrs.
Headache, nausea in 45 min., death in 2-3 hrs.
Headache, nausea in 20 min., death in 1 hr.
Headache, nausea in 5 min., death in 30 min.
Headache, nausea in 1 min., death in 10 min.
10
A
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