6
Engine Emissions - and CO Safety
Potential Effects of CO Exposure
• Work place/industry guidelines for CO exposure limits
• Definition of CO effects
Work place/industry guidelines for CO exposure limits
Limits for permissible exposure to CO vary substantially from region to region. City, State, and Industry
requirements should be consulted prior to use of any equipment. The current Occupational Safety and Health
Administration (OSHA) Permissible Exposure Limit (PEL) for CO is 50 ppm, as an 8-hour time weighted average
(TW A). This is computed by making measurements at intervals over 8 hours, then adding the sums of the
concentrations and the intervals, and dividing by 8 hours. For example:
Time
Interval
PPM
8:00-9:00
1
HR
100
9:00-10:00
1
HR
25
10:00-11:00
1
HR
25
11:00-12:00
1
HR
50
12:00-1:00
1 HR
50
400ppm / 8HR=50pprn TW A
1:00-2:00
1
HR
50
2:00-3:00
1
HR
50
3:00-4:00
1
HR
50
Time intervals =
8 HR
pprn = 400
The current National Institute for Occupational Health and Safety (NIOSH), immediately dangerous to life and
health concentration (IDLH) recommended level for CO is 1,200 ppm. NIOSH defines the IDLH exposure level
as the concentration that could result in irreversible health effects or death, or prevent escape. from the
contaminated environment within 30 minutes.
Definition of CO effects:
The toxic effects of carbon monoxide in the blood are the result of tissue hypoxia (lack of oxygen) carbon
monoxide combines with hemoglobin to form carboxyhemoglobin. Since CO and oxygen react with the same
group in the hemoglobin molecule, carboxyhemoglobin is incapable of carrying Oxygen. The affinity of
hemoglobin for CO is 200 to 240 times greater than for oxygen. The extent of saturation of hemoglobin with CO
depends on the concentration of the gas, the quantity of inspired air and on the time of exposure. The severity
depends on the state of activity of the individual and his tissue oxygen needs.
According to Harrison's Principles of Internal Medicine 7th edition, no symptoms will develop at a concentration
of 0.01 % CO (100ppm) in inspired air, since this will not raise blood saturation above 10 %. Exposure to 0.05%
(500ppm) for 1 hour during light activity will produce a blood concentration of 20% carboxyhemoglobin and result
in a mild or throbbing headache. Greater activity or longer exposure causes a blood saturation of 30 to 50 %. At
this point head ache, irritability, confusion, dizziness, visual disturbance, nausea, vomiting, and fainting can be
experienced. Exposure for one hour to concentrations of 0.1 % (1000ppm) in inspired air the blood will contain
50 to 80% carboxyhemoglobin which results in coma, convulsions, respiratory failure and death. On inhalation of
high concentrations of CO, saturation of the blood proceeds so rapidly that unconsciousness may occur
suddenly without warning.
