What
is carbon monoxide (CO) and why do I need a carbon monoxide
detector?
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:
- Fuel
fired furnaces (non-electric)
- Gas
water heaters
- Fireplaces
and woodstoves
- Gas
stoves
- Gas
dryers
- Charcoal
grills
- Lawnmowers,
snowblowers and other yard equipment
- Automobiles
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.
What
are the medical effects of carbon monoxide and how do
I recognize them?
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.
What
are the different types of carbon monoxide detectors
and how do they work?
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.
Are
some types of detectors better than others? How do I
select the best detector for me?
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.
How
many carbon monoxide detectors should I have and where
should I place them?
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.
What
are the most common causes of carbon monoxide detector
alarms?
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:
- Cracked
furnace heat exchanger.
- Malfunctioning
furnace or water heater.
- Blocked
chimney.
- Other
unpredictable events- vehicle left running in garage,
gas powered device placed near fresh air vent to home,
etc.
Minimizing
preventable events allows everyone to take other less
preventable and predictable events more seriously.
What
should I do when my carbon monoxide detector goes off?
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
can I expect to happen if I 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:
- Your
address.
- The
type of detector that is sounding.
- Whether
or not anyone is feeling ill with 'flu-like' symptoms
as previously described.
- Whether
or not everyone has evacuated the residence.
- The
reading on the detector (if known or available)
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.
Where
can I get further information concerning carbon monoxide
detectors?
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.
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Carbon Monoxide Gas Detectors
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