Carbon monoxide is a colorless, odorless, tasteless and toxic gas produced
as a by-product of combustion. Any fuel burning appliance, vehicle, tool or
other device has the potential to produce dangerous levels of carbon monoxide
gas. Examples of carbon monoxide producing devices commonly in use around the
home include:
The Consumer Products Safety Commission (CPSC) reports that approximately
200 people per year are killed by accidental CO poisoning with an additional
5000 people injured. These deaths and injuries are typically caused by
improperly used or malfunctioning equipment aggravated by improvements in
building construction which limit the amount of fresh air flowing in to homes
and other structures.
While regular maintenance and inspection of gas burning equipment in the
home can minimize the potential for exposure to CO gas, the possibility for
some type of sudden failure resulting in a potentially life threatening build
up of gas always exists.
Carbon monoxide inhibits the blood's ability to carry oxygen to body tissues
including vital organs such as the heart and brain. When CO is inhaled, it
combines with the oxygen carrying hemoglobin of the blood to form carboxyhemoglobin.
Once combined with the hemoglobin, that hemoglobin is no longer available for
transporting oxygen. How quickly the carboxyhemoglobin builds up is a factor of
the concentration of the gas being inhaled (measured in parts per million or
PPM) and the duration of the exposure. Compounding the effects of the exposure
is the long half-life of carboxyhemoglobin in the blood. Half-life is a measure
of how quickly levels return to normal. The half-life of carboxyhemoglobin is
approximately 5 hours. This means that for a given exposure level, it will take
about 5 hours for the level of carboxyhemoglobin in the blood to drop to half
its current level after the exposure is terminated.
The following table describes the symptoms associated with a given concentration
of COHb:
% COHb Symptoms and Medical Consequences
10% No symptoms. Heavy smokers can have as much as 9% COHb.
15% Mild headache.
25% Nausea and serious headache. Fairly quick recovery after
treatment with oxygen and/or fresh air.
30% Symptoms intensify. Potential for long term effects
especially in the case of infants, children, the elderly,
victims of heart disease and pregnant women.
45% Unconsciousness.
50%+ Death.
Since one can't easily measure COHb levels outside of a medical environment,
CO toxicity levels are usually expressed in airborne concentration levels (PPM)
and duration of exposure. Expressed in this way, symptoms of exposure can be
stated as follows:
PPM CO Time Symptoms
35 PPM 8 hours Maximum exposure allowed by OSHA in the
workplace over an eight hour period.
200 PPM 2-3 hours Mild headache, fatigue, nausea and dizziness.
400 PPM 1-2 hours Serious headache- other symptoms intensify.
Life threatening after 3 hours.
800 PPM 45 minutes Dizziness, nausea and convulsions.
Unconscious within 2 hours. Death within 2-3
hours.
1600 PPM 20 minutes Headache, dizziness and nausea. Death within
1 hour.
3200 PPM 5-10 minutes Headache, dizziness and nausea. Death within
1 hour.
6400 PPM 1-2 minutes Headache, dizziness and nausea. Death within
25-30 minutes.
12,800 PPM 1-3 minutes Death.
As can be seen from the above information, the symptoms vary widely based on
exposure level, duration and the general health and age on an individual. Also
note the one recurrent theme that is most significant in the recognition of
carbon monoxide poisoning- headache, dizziness and nausea. These 'flu like'
symptoms are often mistaken for a real case of the flu and can result in
delayed or misdiagnosed treatment. When experienced in conjunction with a the
sounding of a carbon monoxide these symptoms are the best indicator that a
potentially serious buildup of carbon monoxide exists. This comment will be
returned to later.
There are a number of different types and brands of carbon monoxide
detectors on the market today; They can be most easily characterized by whether
they operate on household current or batteries. Underlying this, in most cases,
is the type of sensor employed in the detectors operation. Detectors using
household current typically employ some type of solid-state sensor which purges
itself and resamples for CO on a periodic basis. This cycling of the sensor is
the source of its increased power demands. Detectors powered by batteries
typically use a passive sensor technology which reacts to the prolonged
exposure to carbon monoxide gas.
Regardless of the type of sensor used all detectors sold on the market today
should conform to minimum sensitivity and alarm characteristics. These
characteristics have been defined and are verified by Underwriters Laboratory
in their standard for carbon monoxide detectors UL 2034. This standard was most
recently revised in June of 1995 and went into effect in October of 1995. This
revision specified additional requirements regarding identification of detector
type, low-level (nuisance) alarm sensitivity and alarm silencing. Under no
circumstances should one purchase a detector that is not UL listed.
Each of the two types of detectors mentioned previously has applications in
the home along with associated advantages and disadvantages. The proper
detector for each application or installation should be chosen based on the
application requirements and the products specifications. The following are the
principle advantages and disadvantages of the two different type detectors:
Characteristic Household Current Battery Operated
Cost $30-50 $30-50
Ease of Installation More difficult- requires Less difficult. Can be
outlet near detector or placed anywhere needed.
'hard wiring'.
Maintenance No maintenance required Requires periodic
during life of product replacement of
(5-10 years). Detector battery/sensor module
sensor becomes more every 2-3 years at a
sensitive with age. cost of ~$20.
Reaction Time/Exposure Gives continuous display Reaction time depends
Level Display of CO levels updated on concentration level
every few minutes. and duration of
exposure. Display
information is limited.
Reset Time Will reset immediately Reset time depends on
once CO problem is exposure concentration
corrected. and duration. May
require removal of
sensor pack. A silence
button, however, is now
provided/required.
The Consumer Product Safety Commission recommends a detector on each floor
of a residence. At a minimum, a single detector should be placed on each
sleeping floor with an additional detector in the area of any major gas burning
appliances such as a furnace or water heater. Installation in these areas
ensures rapid detection of any potentially malfunctioning appliances and the
ability to hear the alarm from all sleeping areas. In general, carbon monoxide
detectors should be placed high (near the ceiling) for most effective use.
Detectors should also not be placed within five feet of gas fueled appliances
or near cooking or bathing areas. Consult the manufacturers installation
instructions for proper placement of a detector within a given area.
There are many conditions which can cause a carbon monoxide detector to
alarm. Most are preventable and few are actually life threatening. Ideally
through proper placement of the detector and education of the users the number
of preventable calls can be minimized and activation will only occur in the
more serious situations.
Preventable causes of CO alarm activation and the recommended preventive
action are as follows:
Cause Preventive Action
Inadequate fresh air venting of the Have a heating contractor install a
home. fresh air makeup system in the home
Running gas powered equipment or Gas powered equipment or vehicles
automobiles in a home or garage should never be operated within a
home or garage- even if the garage
door is open. Since most homes are
typically at a lower pressure
relative to outside air, the gas can
actually be drawn into the home.
Charcoal grilling in the home or Charcoal grilling is a tremendous
garage. producer of carbon monoxide gas.
Charcoal grills should never be
operated in the home.
Malfunctioning appliances or All fuel burning appliances or
equipment in the home. equipment in the home needs periodic
inspection and preventive
maintenance. While all fuel burning
appliances will produce some CO gas,
regular preventive maintenance can
keep this to a minimum.
Malfunctioning or overly sensitive Buy only UL Listed alarms conforming
alarm. to the latest revision (June 1995)
of UL standard 2034. This revision
includes new requirements to minimize
nuisance alarms.
While many causes can be prevented others can not and may occur
unpredictably. Not only are these problems harder to predict but they also tend
to be more serious in nature. Examples of these type problems are:
Minimizing preventable events allows everyone to take other less preventable
and predictable events more seriously.
First and foremost, stay calm. As mentioned previously most situations
resulting in activation of a carbon monoxide detector are not life threatening
and do not require calling 911. To determine the need to call 911, ask the
following question of everyone in the household:
"Does anyone feel ill? Is
anyone experiencing the 'flu-like' symptoms of headache, nausea or
dizziness?"
If the answer to the above by anyone in the household is true, evacuate the
household to a safe location and have someone call 911. Failure to evacuate
immediately may result in prolonged exposure and worsening effects from
possible carbon monoxide gas. The best initial treatment for carbon monoxide
gas exposure is fresh air.
If the answer to the above by everyone in the household is no, the
likelihood of a serious exposure is greatly diminished and one probably does
not need to call 911. Instead, turn off any gas burning appliances or
equipment, ventilate the area and attempt to reset the alarm. If the alarm will
not reset or resounds, call a qualified heating and ventilating service
contractor to inspect your system for possible problems. If at any time during
this process someone begins to feel ill with the symptoms described above
evacuate the household to a safe location and have someone call 911.
What to expect when calling 911 is based on the polices and procedures of
the public safety agencies serving your community and will vary from area to
area. Most public safety agencies are, however, recognizing the dangers posed
by carbon monoxide gas and are adopting similar procedures to the ones
described below. These procedures are based on information developed by the
International Association of Fire Chiefs (IAFC) and other national and regional
associations. The objective of these procedures is to quickly determine the
severity of the situation and provide the proper emergency response. The
following is a summary of what one can expect to happen if the call 911 because
a carbon monoxide detector is sounding:
When initially calling 911 be prepared to provide the following information:
The dispatcher will determine the response required based on the answers to
the above- most significantly whether or not anyone is feeling ill.
If anyone is feeling ill and/or you can not or have not been able to
evacuate everyone, law enforcement, medical and fire personnel will be assigned
to the call on an emergency basis. Law enforcement to assist with the immediate
evacuation of individuals, medical to treat any victims and fire to monitor for
CO gas and assist with the other activities.
If no one is feeling ill, you may be advised to contact your local heating
contractor or gas company to assist you or, more likely, fire personnel will be
dispatched on a routine basis to monitor for CO gas and advise if a 'real'
carbon monoxide problem exists.
As mentioned previously, response policies vary by community and you may
wish to call your local fire or police non-emergency number to ask what their
particular policies are. An example
standard operating procedure for CO alarms is attached. This policy is
based on the IAFC model procedures and has been adopted by the Hennepin County Fire
Chiefs Association as their 'standard' policy for fire departments which are
part of that association.
Several manufacturers of carbon monoxide detectors offer toll free numbers
for additional information regarding their products. These numbers are as
follows:
Manufacturer Number
American Sensors 800-387-4219
Enzone 800-448-0535
First Alert 800-323-9005
Jameson 800-779-1719
Nighthawk 800-880-6788
Quantum 800-432-5599
Radio Shack Contact your local store
S-Tech 800-643-5377
Additional information with product ratings is contained in the July 1995
Consumer Reports issue on home safety products. One word of note regarding the
ratings in this issue- the products tested have probably since be replaced by
updated models conforming to the revised UL 2034 standard which took effect in
October 1995. Check with the manufacturer for current information.
This information provided as a public
service by the Hamel Volunteer Fire Department.
Comments or questions concerning this document should be directed to:
Copyright 1995, H. Brandon
Guest and Hamel Volunteer Fire Department
Rights to reproduce granted provided copyright information and this
statement included in their entirety. This document provided for informational
purposes only. No warranty with respect to suitability for use expressed or
implied.