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Knowledge Base:  
Carbon Monoxide and Portable Generators
Last Updated: 01/21/2009
Portable generators use combustion engines like lawn mowers to generate electricity.  The combustion process creates fumes that include carbon monoxide (CO), which can kill people.  Locating the generator in an attached garage with the door open in no way guarantees that the combustion fumes will flow out of the garage.  In fact, it almost does the opposite.  Building pressures may drive the combustion fumes through any crack or opening between the house and the garage.  It is critical that the generator be located outside the house, away from any openings – vents or windows – that might allow the fumes to flow back into the house.  Please follow the manufacturers instructions and warnings.  Don’t be lulled into throwing caution away because it is an extraordinary situation.

(Note that the same precautions apply to any combustion appliance that is used in the living space that includes kerosene heaters or gas ovens.)

CO is measured in parts per million or ppm.  The short term maximum exposure allowed by the Environmental Protection Agency (EPA) is 9 ppm over 8 hours or 35 ppm for 1 hour.  Typical UL listed CO alarms provide no CO warning below 30 ppm.  An excellent CO monitor that provides effective, low-level response is available from COExperts.
 The effects of CO poisoning at various levels is as follows:

1 -2 ppm          Common ambient levels from cooking stove, traffic outside

15 – 20 ppm    Impaired performance in time discrimination and decreased time to angina response.

20 ppm            Typical concentration in chimney gases of a properly operating furnace or water heater

30 ppm            Earlier onset of exercised induced angina

35 ppm            Maximum allowable outdoor concentration for one-hour period in any year (EPA)

50 ppm            Fire departments require use of self-contained breathing apparatus for exposures above 50ppm

75ppm             Significant decrease in oxygen researve available to the myocardium

100 ppm          Slight headache, tiredness, dizziness, nausea after several hours exposure.

200 ppm          Maximum recommended workplace exposure.  Headache, tiredness, dizziness, nausea after 2-3 hours.

400 ppm          Frontal headaches within 1-2 hours, life-threatening after 3 hours, maximum parts per million in flue gas

500 ppm          Commonly occurs in garages when a cold car is started in an open garage and warmed for 2 minutes

800 ppm          Dizziness, nausea and convulsions within 45 minutes.  Unconsciousness within 2 hours.  Death in 2-3 hours.

1,600 ppm       Headache, dizziness and nausea within 20 minutes.  Death within 1 hour.  Smoldering wood fires, malfunctioning furnaces, water heaters, and kitchen ranges typically produce concentrations exceeding 1,600 ppm

3,200 ppm       Headaches, dizziness, and nausea within 5 -20 minutes.  Quickly impaired thinking.  Death within 30 minutes

6,400 ppm       Headache, dizziness, and nausea within 1-2 minutes.  Thinking impaired before response possible.  Death within 10-15 minutes

12,800 ppm     Death within 1-3 minutes

70,000 ppm     Typical tailpipe exhaust concentrations from cold gasoline engine during the first minute of a cold weather start.  Concentrations decrease to 2 ppm after 17 minutes of running.

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