will not be operational and will not monitor for
smoke and CO levels without battery.
WARNING! -
This apparatus is designed to
protect individuals from the acute effects of
carbon monoxide exposure. It may not however,
prevent the chronic effects of carbon monoxide
exposure and will not fully safeguard individuals
at special risk or with specific medical
conditions. If in doubt consult a medical
practitioner.
7. Carbon monoxide (CO) overview
7.1 Toxic effects
Carbon monoxide (CO) is a colourless, odourless,
non-irritating gas classified as a chemical
asphyxiant and whose toxic action is a direct result
of the hypoxia produced by a given exposure.
CO is rapidly absorbed through the lungs, diffuses
across the alveolar capillary membrane and is
reversibly bound with haemoglobin as
carboxyhaemoglobin (COHb), however, a minute
amount is present in the plasma. The affinity of
haemoglobin for CO is over 200 times its affinity
for oxygen. This reduces the oxygen carrying
capacity of the blood, and has an effect on the
dissociation of oxyhaemoglobin, which further
reduces the oxygen supply to the tissues. CO is
chemically unchanged in the body, and is eliminated
in expired air. The elimination is determined by the
same factors that applied during absorption. The
half-life while breathing room air is 2 h - 6,5 h
depending on the initial COHb level.
If the CO level in the inhaled air is constant, the
level of COHb in the blood will approach an
equilibrium (saturation) state after several hours.
However, the rate at which the equilibrium is
reached depends on many factors, e.g. lung
ventilation rate (physical activity) and alveolar
capillary transfer, cardiac parameters, blood
haemoglobin concentration, barometric pressure,
oxygen and carbon dioxide concentration in the
inhaled air, but the two most important factors in
determining the COHb level are the CO
concentration and the duration of exposure.
The effects of different saturation blood COHb
levels on healthy adults are shown in Table 7.1.
Table 7.1 – Health effects of COHb blood levels on
healthy adults
% COHb
Effects
0.3 – 0.7 Normal range in non-smokers due to
endogenous CO production
0.7 – 2.9 No proven physiological changes
2.9 – 4.5 Cardio-vascular changes in cardiac patients
4 – 6
Usual values observed in smokers, impairment
in psychomotor tests
7 – 10
Cardio-vascular changes in non-cardiac patients
(increased cardiac output and coronary blood
flow)
10 – 20
Slight headache, weakness, potential burden on
foetus
20 – 30
Severe headache, nausea, impairment in limb
movements
30 – 40
Severe headache, irritability, confusion,
impairment in visual acuity, nausea, muscular
weakness, dizziness
40 – 50
Convulsions and unconsciousness
60 – 70
Coma, collapse, death
Source: U.S. Environmental Protection Agency 1984
The relationship between the CO concentration and
the duration of exposure can be calculated for a
given %COHb, by parameterising the above factors.
Figure 7.1 shows examples for a person undertaking
light/moderate exercise.
Figure 7.1–Relationship between CO concentration and
exposure time for various %COHb (light/moderate exercise)
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GS883-A Instruction Manual Rev. G
