Carbon monoxide is responsible for more than half of the poisoning fatalities in industrial settings because it has no warning properties.  It is generated due to incomplete combustion of organic fuels, especially as created by the exhaust of internal combustion engines.

Exposure to carbon monoxide decreases the ability of the blood to carry oxygen to the tissues.  This is known as hypoxia.  Carbon monoxide poisoning represents a multi-system failure that affects the cardiac and central nervous systems, which are particularly sensitive to hypoxia.  It also aggravates heart and artery diseases which may cause problems in those with pre-existing heart problems.  Pregnant  women and smokers are more susceptible to the effects.  The effects are also more severe in jobs which heavy labor and/or high temperatures at high elevations (over 5,000 feet above sea level).

Hypoxia can be particularly harmful to brain function.  Even as relatively how levels of exposure (25 to 100 ppm), carbon monoxide exposure can effect judgment and reaction time.  This effect can in increase the potential for accidents, particularly among equipment operators.

Early signs are lassitude, headache, dizziness and possibly nausea.  These signs often go unrecognized.  Higher concentrations can cause headaches, dizziness, nausea, weakness, mental confusion and abnormal nd rapid breathing.  The skin becomes slightly bluish and may lead to a bright reddish color under the fingernails.  Occasionally hallucinations may occur.  With continued exposure to high concentrations, weakness and dizziness may be the only warning sign before losing consciousness followed by coma.  in some cases after treatment and recovery from a coma there is residual loss of vision, but the pupils are reactive to light indicating the damage is related to the cortex of the brain.  A syndrome of headaches, fatigue dizziness, paralysis , chest pain, palpitations and visual disturbances has been associated with chronic carbon monoxide poisoning.