1. Carbon monoxide is an odorless, colorless, tasteless gas.  It is undetectable by human senses.  (If someone tells you they smell carbon monoxide, they’re dreaming.  They are smelling other odors, but they are not smelling carbon monoxide.)
  2. You could be in a room filled with carbon monoxide and NOT notice it.  It is non-irritating so the body does not react to it, does not detect it, but it readily absorbs it.
  3. Carbon monoxide is a byproduct of incomplete combustion of just about anything that burns.
  4. All flames produce some amount of carbon monoxide.  This includes cigarettes and cigars, pipe tobacco, candles, gas stoves, gas ovens, gas space heaters, gas fireplaces and gas furnaces.
  5. Gas appliances that have adequate air and are properly adjusted produce LESS carbon monoxide than a lit cigarette.
  6. Carbon monoxide poisoning is NOT caused by faulty appliances, it is caused by “faulty” air movement. Gas appliances produce large quantities of carbon monoxide when they are forced to burn oxygen-depleated air or re-burn their exhaust gasses.  (Yeah, I know, misadjusted equipment can produce CO, but if nothing else is wrong, the CO goes up the flue.)
  7. A gas appliance with a properly connected and sized flue, even with the poorest possible adjustments and operating conditions, will not introduce carbon monoxide into a house.  The carbon monoxide will vent up the flue.
  8. A properly operating gas appliance with a blocked or defective flue can kill you because the combustion products are venting into the home.
  9. Gas appliances and flues should be checked at least yearly.
  10. Contrary to media reports, thousands of people do NOT die each year in the U.S. due to carbon monoxide poisoning from gas appliances.  Hundreds of people do NOT die each year in the U.S. due to carbon monoxide poisoning from gas appliances.  (This information is readily available from the CPSC, go check.)
  11. On average, less than 100 people die each year in the U.S. due to carbon monoxide poisoning from gas appliances.  (That’s according to CPSC records from 1994 to 2006.)
  12. The human body produces and uses carbon monoxide in very small quantities.
  13. The effects of carbon monoxide poisoning can be minimized by moving to fresh air.  The effects can be reduced more quickly by administering 100% oxygen, and even faster by using a hyperbaric chamber.
  14. It takes over 5-1/2 hours to eliminate 50% of the carbon monoxide in the body after a high level exposure by moving to fresh air.
  15. It also takes over 5-1/2 hours to eliminate 50% of the carbon monoxide in the body after a low level exposure by moving to fresh air.
  16. Carbon monoxide alarms do allow fairly high level exposure before they alarm.  Typical alarms purchased at hardware and big-box stores should NOT be relied on to protect infants or the elderly.
  17. Carbon monoxide alarms should NOT be relied on as the sole protector against CO poisoning.  CO detectors may not alarm under low humidity conditions or when there are “confused” by other gasses.
  18. Carbon monoxide alarms should be replaced at least every five years.  Two manufacturers have introduced CO detectors that have end-of-life circuits in them and will chirp when they should be replaced.  The new detectors have a seven year life.
  19. Carbon monoxide alarms can be damaged and rendered useless by being exposed to concentrations of Freon (refrigerant.)
  20. Carbon monoxide alarms may be triggered by other gasses such as; hair spray, alcohol, carbon dioxide (dry ice), cleaning fluids, paint thinners, acetone, fingernail polish, polish remover, aerosol propellants and other petroleum-based vapors.
  21. Carbon monoxide effects vary by the individual.  If a room full of people are exposed to high levels of carbon monoxide, most will have headaches, some will have nausea, some will act like they are intoxicated (slurred speech, poor balance) and a few will feel weak.
  22. The chart below lists the most common symptoms and how often they are noted when a carbon monoxide incident is reported.

 

Clinical Symptoms of Acute
Carbon Monoxide Poisoning
 Symptom

Frequency
 Headache

 90%
 Nausea and vomiting

 50%
 Lethargy

 50%
 Altered conscious level

 30%
 Subjective weakness

 20%

  Less frequent symptoms:

  Arrhythmias

  Pulmonary oedema

  Hypotension

  Coma

  Exacerbation of existing disease

  Confusion

  Depression

  Ataxia

  Hearing problems

 

  • Carbon monoxide detectors are designed to DELAY their alarm in an effort to prevent nuisance alerts.  The delay varies based on the concentration of CO.

    These are the CO concentrations and timings at which current carbon monoxide detectors are supposed to sound an alarm, based on the UL-2034, 2005 standards.

  • Must alarm when exposed to:
    • 70 PPM – at between 60 & 240 minute of continuous exposure
    • 150 PPM – at between 10 & 50 minutes of continuous exposure
    • 400 PPM – at between 4 & 15 minutes of continuous exposure
  • Ignore CO levels less than 30 PPM for at least 30 days and ignore levels of 70 PPM or less for at least an hour. This requirement was included by UL at the request of gas utilities and firefighters to reduce the number of unnecessary emergency calls from homeowners.

 

Carbon Monoxide Levels
and Potential Effects


Carbon Monoxide Concentration
ppm = parts per million

Exposure Limits & Effects 

 As posted by various safety and engineering organizations.

9

ASHRAE 62-89: – The maximum allowable concentration for continuous (24-hour) exposure. ASHRAE states the ventilation air shall meet the outdoor air standard referenced to EPA and 9 PPM.

9

U.S. Environmental Protection Agency: 9 PPM – This level or lower as an ambient air quality goal averaged over eight hours. This outdoor air standard is exceeded in many urban areas due to auto exhaust.

30

UL 2034 (Underwriters Laboratories, CO alarm detector designation): 30 PPM is the concentration required for UL 2034 listed alarms to sound when this concentration is present for 30 days minimum. This allows the sensor to clear itself. People of vulnerable health may require alarms with lower PPM concentration trigger levels. (NOTE: Alarms listed under UL 2034 may not have been able to meet this requirement.)

10 – 35

Cautionary chronic levels: 10–35 PPM is a marginal level in reference to potential or foreseeable problems in some situations. Occupants should be advised of a potential health hazard to infants and small children, elderly people and persons suffering from respiratory or heart problems. If a building has an attached auto garage, CO levels should be documented there. Accept this level as normal where unvented appliances are in use. These levels are unacceptable when originated from vented appliances.

35

EPA: – This level or lower as an ambient air quality goal averaged over one hour outside. Common action level: 35 PPM is a common action level where emergency responders should utilize self contained breathing apparatus if sustained occupation of the area is required. 35 PPM or less averaged over an eight-hour day within that workday is a common goal of certain states’ occupational health and safety agencies. This is also a common goal of many employers despite higher regulated concentra­tion standards and may require the measurement of several simultaneous reference locations. Max safe level for 8 hrs (OSHA). Normally no physical effects for short exposure periods.

50

OSHA: 50 PPM – Maximum allowable concentration for a worker’s continuous exposure in any eight-hour period. This eight-hour average requires continuous measurement and accurate reporting in the workplace. The 8-hour PEL for CO in maritime operations is also 50 ppm. Maritime workers, however, must be removed from exposure if the CO concentration in the atmosphere exceeds 100 ppm. The peak CO level for employees engaged in Ro-Ro operations (roll-on roll-off operations during cargo loading and unloading) is 200 ppm. NFPA FSH 8 hour exposure limit.

70

UL 2034: 70 PPM concentration required for UL 2034-listed CO alarms to sound when concentration is present for no more than 240 minutes (four hours) or as early as 60 minutes (one hour)

36 – 99

Foreseeable hazardous levels: 36–99 PPM is excessive. Medical alert and health consultation is advised especially if levels displayed chronic conditions. Evacuate the area. Air packs are recommended if sustained conditions and presence required. Conditions must be mitigated. Ventilation required.

100 – 199

Evacuation advisory levels: 100–200 PPM is a common building evacuation standard and is dangerous. Medical alert conditions exist. Occupant health inquiries should be conducted. Exposed occupants should have someone else transports them to seek medical help. 15-minute maximum exposure upon discovery.

150

UL 2034: 150-PPM concentration required for UL 2034 listed CO alarms to sound when concentration is present for no more than 50 minutes or as early as 10 minutes.

200

Evacuation Required! 200 PPM is universally accepted as an evacuation action level. Occupant health inquiries should be conducted. Exposed occupants should have someone else transports them to seek medical help. 15-minute maximum exposure upon discovery. Building should be ventilated and searched for additional occupants. Combustion systems should be thoroughly tested for CO production and dispersion. Max safe level for 1 hr (OSHA). NFPA FSH: Slight headache within 2 to 3 hours.

400

UL 2034: 400-PPM concentration required for UL 2034 listed CO alarms to sound if concentration is present for no more than 15 minutes or as early as four minutes. Frontal headache within 1 to 2 hours. Widespread headache after 3 hours. NFPA FSH: headache, nausea after 1 – 2 hours.

800

Headache, dizziness, nausea, convulsions within 45 minutes. Loss of consciousness within 2 hours. NFPA FSH: loss of consciousness after 1 hour.

1,000

NPFA FSH: Loss of consciousness after 1 hr expsosure

1,600

Collapse and possible death within 1 hour. NFPA FSH: Headache, dizziness, nausea within 20 minutes.

3,200

Headache, dizziness within 10 minutes. Unconsciousness and danger of death within 30 minutes. NFPA FSH: Headache, nausea, dizziness after 5 – 10 minutes; collapse and unconsciousness after 30 minutes.

6,400

NFPA FSH: Head, dizziness after 2 minutes, unconsciousness and death after 10-15 minutes

12,800

NFPA FSH: Immediate physiological effects, unconsciousness and danger of death within 1 – 3 minutes.

ASHRAE: American Society of Heating, Refrigeration and Air-Conditioning Engineers OSHA: Department of Labor, Occupational Safety and Health Administration EPA: Environmental Protection Agency.
 
UL: Underwriters Laboratories – UL2034 is the current standard used by CO detector manufacturers.
NFPA FSH: National Fire Protection Association Fire Safety Handbook, 19th Edition.

Where agency designations are not given, the information was taken from medical journals, municipal and fire-department notices and manufacturer’s articles. There seems to be only anecdotal evidence to support the symptoms at certain carbon monoxide levels.