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.)
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
Carbon monoxide is a byproduct of incomplete combustion of just about
anything that burns.
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 appliances that have adequate air and are properly adjusted produce LESS
carbon monoxide than a lit cigarette.
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.)
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.
A properly operating gas appliance with a blocked or defective flue can kill
you because the combustion products are venting into the home.
Gas appliances and flues should be checked at least yearly.
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.)
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.)
The human body produces and uses carbon monoxide in very small
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.
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.
It also takes over 5-1/2 hours to eliminate 50% of the carbon monoxide in the
body after alow level exposure by moving to fresh air.
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.
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.
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.
Carbon monoxide alarms can be damaged and rendered useless by being exposed
to concentrations of Freon (refrigerant.)
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.
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
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
Nausea and vomiting
Altered conscious level
Less frequent symptoms:
Exacerbation of existing disease
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
Exposure Limits & Effects
As posted by various safety and engineering
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.
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
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.
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.
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
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.
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
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.
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.
Headache, dizziness, nausea, convulsions within 45 minutes.
Loss of consciousness within 2 hours. NFPA FSH: loss of consciousness after 1
NPFA FSH: Loss of consciousness after 1 hr
Collapse and possible death within 1 hour. NFPA FSH:
Headache, dizziness, nausea within 20 minutes.
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.
NFPA FSH: Head, dizziness after 2 minutes,
unconsciousness and death after 10-15 minutes
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
UL: Underwriters Laboratories – UL2034 is the current standard used by CO
detector manufacturers. NFPA FSH: National Fire Protection Association Fire Safety Handbook,
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.
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