User Manual

ENMET Corporation ISA 200 RAL (O)
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Appendix AAppendix A
The Characteristics and Effects of Carbon Monoxide
Carbon monoxide is a colorless odorless toxic gas generated by incomplete combustion of a hydrocarbon fuel in air. It
may be present where internal combustion engines, furnaces, boilers, and other combustion devices are present. It is
toxic when inhaled because of its great affinity to hemoglobin, the oxygen carriers in the red cells of the blood. CO
replaces the oxygen normally carried by the hemoglobin, and thus inhibits the delivery of oxygen throughout the body;
the victim suffers from oxygen deficiency, and may die from asphyxiation. The symptoms and degree of danger
resulting from exposure to CO depend upon the concentration of the gas and the length of exposure; this is shown in
Figure 8. The ISA-200 RAL(O) instrument is employed to warn the user of the presence of CO, and to facilitate the
assessment of the degree of danger that he or she is exposed to.
Based upon knowledge of the effects of CO, the Occupational Safety and Health Authority (OSHA) has set limits on
exposure to CO in the workplace. These are 35 ppm (parts CO per million parts air) as an time weighted average for
an eight hour day, and a maximum exposure of 200 ppm. For compressed air line applications, OSHA requires Grade
D breathing air supplied, using a Compressed Gas Association (CGA) definition (G-7.1). Depending on interpretation
of the OSHA respiratory standard, 10 ppm and 20 ppm CO have been used as maximum limits and standard
instrument alarm points.
The ISA-200 RAL(O) has two preset alarm set points, at 10 ppm and 20 ppm CO, which are adjustable, but cannot be
set below 5 ppm or above 100 ppm.
The curves below are for percent carboxalhemoglobin with 50% being the top curve, 5% the bottom. %COHb is a
measure of the amount of hemoglobin occupied by CO rather than oxygen. CO effects upon children, adults engaging
in physical activity, and smokers, are ore pronounced.
Figure 11: Carbon Monoxide Concentration