Carbon Monoxide and Health Effects

A comprehensive guide to carbon monoxide (CO) poisoning symptoms, health effects, and exposure concentration thresholds. Includes data on toxic symptoms at various CO concentrations and inhalation times.

Carbon Monoxide and Health Effects

Carbon monoxide - CO - is an odorless, tasteless, colorless and toxic gas.

Carbon Monoxide Poisoning Symptoms

Low to Moderate Poisoning

  • Headache
  • Fatigue
  • Shortness of breath
  • Nausea
  • Dizziness

Severe Poisoning

  • Confusion
  • Vomiting
  • Loss of muscle coordination
  • Unconsciousness

Carbon monoxide is a by-product from combustion processes. Any combustion process, fuel burning appliance, vehicle or other device has the potential to produce toxic carbon monoxide gas.

Carbon monoxide is dangerous because it inhibits the blood's ability to carry oxygen to vital organs such as the heart and brain. Inhaled CO will combine with the oxygen carrying hemoglobin in the blood and will form carboxyhemoglobin (COHb) which is not usable for oxygen transport.

CO Concentration (ppm)Inhalation TimeToxic Symptoms
9Short term exposureASHRAE recommended maximum allowable concentration in living area
358 hoursThe maximum exposure allowed by OSHA in the workplace over an eight hour period
2002-3 hoursSlight headache, tiredness, fatigue, nausea and dizziness
4001-2 hoursSerious headache-other symptoms intensify. Life threatening after 3 hours
80045 minutesDizziness, nausea and convulsions. Unconscious within 2 hours. Death after 2-3 hours
160020 minutesHeadache, dizziness and nausea. Death within 1 hour
32005-10 minutesHeadache, dizziness, nausea. Death within 1 hour
64001-2 minutesHeadache, dizziness, nausea. Death within 25-30 minutes
128001-3 minutesDeath within 1-3 minutes
Exposure (hours)Perceptible (ppm)Sickness (ppm)Deadly (ppm)
0.560010002000
12006001600
21003001000
450150400
625120200
825100150