BACKGROUND:
The composition of diesel exhaust gases vary with the type of engine and with the rate of operation of
these diesel engines. The prominent noxious gases of diesel engines are NOX [which is made up of NO
(nitric oxide) and NO
2
(nitrogen dioxide)], followed by CO (carbon monoxide), SO
2
(sulfer dioxide) and
SO
4
(sulfates).
Carbon monoxide (CO) sensors do a good job of detecting gasoline engine exhaust fumes, but because
diesel engines output a smaller amount of carbon monoxide, (less than 1%) CO detection is not recom-
mended for sensing diesel exhaust. There are no stable, inexpensive, or easy to maintain sensors for
sensing nitric oxide or nitrogen dioxide which are the poisonous and the dominant diesel exhaust emis-
sions. An investigation R18884*, done by the U.S. Department of Interior, Bureau of Mines shows that
the carbon dioxide (CO
2
) in diesel exhaust is relative to all the noxious gases contained within the diesel
exhaust.
The Bureau report states “CO
2
is present in the diesel exhaust gases in the highest concentration of any
of the pollutants,” (13%). It further states “CO
2
is the only stable and nonreactive pollutant in the ex-
haust that is unaffected, to any appreciable extent, by time, emission control devices, or engine wear.” For
these reasons CO
2
is chosen to be the surrogate gas to be sensed to indicate dangerous levels of the
noxious gases contained in diesel exhaust.
The report “established an estimate level of CO
2
–0.133 pct (percent) at which the other diesel pollutants
are considered below harmful levels.” The 0.133 percent would be equivalent to 1330 ppm of CO
2
. There-
fore if the CO
2
in environments where diesel exhaust is present is kept at or below 1300 ppm, a safe
environment will be maintained.
* Report of Investigation 8884:
Diesels in Underground Mining, A review and an Evaluation of an Air
Quality Monitoring Methodology by J. Harrison Daniel, Jr., Staff Engineer, Division of Health & Safety,
Bureau of Mines, Washington, D.C.
•
Operating principle: Non Dispersive Infrared
• Gas sampling method: Diffusion
• Range: 0 to 2000 ppm
• Response time: Less than 1 minute
• Operating temperature range: 32ºF to 122ºF
(0ºC to 50ºC)
• Operating humidity: 0-90% RH (non condensing)
• Dimension: 5.2” x 3.2” x 1.4”
• Weight: .5 lbs. (.35 kg)
SPECIFICATIONS
TOXALERT INTERNATIONAL, INC., P.O. BOX 159, MOUND, MINNESOTA 55364 (952) 472-4541 FAX (952) 472-4960
Visit our website at www. toxalert. com
• Accuracy: + 5% of reading or + 75 ppm, which ever is
greater
• Repeatability: + 20 ppm
• Typical Drift (per year): + 75 ppm ( @1200 ppm)
• Storage temperature: -22ºF to 140ºF
(-30ºC to 60ºC)
• Input power: 20-30 VAC (provided from GVU
Control unit)
• Power Consumption: Less than 2W @24VAC
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(4 pages)
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