F requently A sked Q uestions About Carbon Monoxide Detectors
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.
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% |
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. Nausea and serious headache. Fairly quick recovery after |
| 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 outlet near detector or 'hard wiring'. |
Less difficult. Can be placed anywhere needed. |
| Maintenance |
No maintenance required during life of product (5-10 years). Detector sensor becomes more sensitive with age. |
Requires periodic replacement of battery/sensor module every 2-3 years at a cost of ~$20. |
Reaction Time/Exposure Level Display |
Gives continuous display of CO levels updated every few minutes. |
Reaction time depends on concentration level and duration of exposure. Displayinformation is limited. |
| Reset Time |
Will reset immediately once CO problem is corrected. |
Reset time depends on exposure concentration 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:
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.
