Environmental Engineering Reference
In-Depth Information
Table 3.7
Human Responses Associated with Different Blood COHb Levels
Blood COHb
level
Effect
0-1%
None
2.5%
Impairment of time interval discrimination in nonsmokers.
2.8%
Onset of angina pectoris pain shortened in exercising patients;
duration of pain lengthened.
3.0%
Changes in relative brightness thresholds.
4.5%
Increased reaction time to visual stimuli.
10%
Changes in performance in driving simulation.
10-20%
Headache, fatigue, dizziness, loss of coordination.
Source:
From NACPA, USDHEW,
Publication No. AP-62
, Washington, D.C., 1970.
Well-documented human responses to short-term CO exposures expressed
Carbon monoxide exposures can affect individuals with cardiovascular
disease. The lowest observed physiological effect level for patients with exer-
cise-induced ischemia (tissue O
2
deficiency) is somewhere between 3 and 4%
COHb. Exposure to enough CO to produce 6% COHb appears to be sufficient
to cause arrhythmia in exercising patients with coronary artery disease. There
is suggestive evidence that CO exposure may increase the risk of sudden
death from arrhythmia in such patients. In addition, epidemiological studies
indicate that a significant relationship may exist between increased CO expo-
sure and increased mortality and cardiovascular system complaints.
Several studies have been conducted in hospital emergency rooms to
evaluate the incidence of elevated COHb levels (
10%) in patients with
influenza-like or neurologic symptoms. In the first case, 24% of patients with
flu-like symptoms had blood COHb levels
≥
10%. In the second case, 3% of
patients reporting neurologic symptoms had elevated COHb; incidence
increased to 12% when only individuals with gas-fueled heating systems
were considered. These studies indicate that subacute CO poisoning is com-
monly misdiagnosed.
The effects of chronic exposures to relatively low levels of CO are
unknown. There is evidence from animal studies to suggest that CO expo-
sures may contribute to atherosclerosis.
The effects of CO are likely to differ among those exposed. Subpopula-
tions at higher risk would include the unborn, infants, the elderly, individ-
uals with preexisting disease that decreases O
2
availability, and individuals
using certain medications and recreational drugs.
≥
B. Irritants
Combustion-generated contaminants include a number of mucous mem-
brane and upper respiratory system irritants. Most notable are aldehydes
such as HCHO, and in some cases acrolein, RSP, and SO
2
. Aldehydes are
common irritants of the eyes, nose, throat, and sinuses. Respirable particles
