What is Carbon Monoxide (CO)?
Why is it Dangerous?
- CO is a colorless, odorless, tasteless gas
- It is a by-product of incomplete combustion (unburned fuel such as gas, oil,wood, etc.)
- Low concentrations of CO can go undetected and can contribute to ongoing, unidentified illnesses. At high concentrations, it can be deadly
If there is CO in the air you breath, it will enter your blood system the same way oxygen does, through your lungs. The CO displaces the oxygen in your blood, depriving your body of oxygen. When the CO displaces enough oxygen, you suffocate.
What are the Symptoms?
Continued exposure or high concentrations –
- Severe headaches
- Cardiac problems
- Breathing difficulties
- Brain damage
Long term exposure to low concentrations –
Why is it called "The Great Imitator"?
- Slight headaches
- Shortness of breath with only moderate exertion
- Dizziness and confusion
Who is at Greater Risk?
- Symptoms of CO poisoning are very similar to the flu
- Illness in your pets just preceding illness in a family member may suggest CO poisoning
- Senior citizens
- Unborn babies
- People with respiratory or coronary problems
- Pregnant women
- Young children
Note: Vulnerable people who are exposed even to low levels of CO for long time periods may have similar health affects as those exposed to high concentrations of CO.
What can Produce CO in our Homes?
Anything that burns fuel or generates combustion gases including -
- Gas Stoves
- Space heaters
- Water heaters
Solid fuels, such as wood, always produce carbon monoxide when they are burned. Gas and liquid fuels may produce no CO or very little.
What are the most common sources of Carbon Monoxide?
- Automobile exhaust in attached garages.
This is responsible for 60% of all CO alarms. People who warm their cars
up in the garage are trapping CO inside the garage. The CO can find its way into the home.
- Gas cooking appliances
Reported to account for 20% of CO alarms. May be a result of a misused, poorly
maintained, poorly installed, or unvented cooking appliance.
3.1 Poor draft/venting for fuel burning appliances – This is one of the most common and serious causes for CO build up and has been reported to account for up to 19% of CO alarms. The products of combustion are not being safely expelled to the exterior. This could be due to venting problems, such as blocked chimney flues or inadequate venting for appliances or fireplaces. Other problems include poor installation and negative air pressure in the house, causing backdrafting, often due to exhaust fans.
Other problems include:
3.2 Poor combustion at furnace - Inadequate combustion air to the furnace can result in incomplete combustion.
If the furnace has a cracked heat exchanger, it is possible to get CO into the circulating air. It is also imperative that we do not deprive our heating
equipment and fuel burning appliances of air; especially in air-tight homes where running exhaust fans can result in a shortage of combustion air. Combustion air is essential for safe operation of furnaces, water heaters, and other fuel burning equipment.
3.3 Leakage – A leak in a chimney or flue pipe.
3.4 Ventilation – Barbecues or gasoline powered equipment operating in a attached garage, basement,
or enclosed area.
Are there more problems with carbon monoxide today than 30 years ago?
Yes, due to -
More energy-efficient, air-tight homes
Less natural ventilation
How can I guard against carbon monoxide poisoning?
The first line of defense is to have your home heating systems, fuel burning appliances, flues and chimneys checked and/or cleaned annually.
Specialists should check for:
Blocked openings to flues and chimneys
Cracked,rusted,or disconnected flue pipes
Rusted or cracked heat exchangers
Soot or creosote build-up inside fireplaces and chimney flues
Exhaust or gas odors.
Attached garages require gas proofing and automatic closers for doors into the home
Adequate combustion air
Adequate venting on indoor combustion appliances (i.e-gas stoves)
The second line of defense is a CO detector.
Carbon Monoxide Detectors
Introduced in the early 1990’s
Designed to warn homeowners when CO reaches dangerous levels within the
How do they work?
CO detectors sample the air at specific time intervals
A microchip inside the detector stores the reading and keeps track of
the level of CO that the detector is exposed to over time
Types of sensors:
Biometric (Oldest type of sensor)
Metal Oxide Semi-conductor
Electrochemical (The best of the three types for a residential sensor)
Infrared – Highly advanced, very expensive. Not something you would
find at Home Depot.
The detectors are supposed to sound an alarm when exposed to a set level
of CO (measured in parts per million) over a specific time period. These
standards are set by UL (Underwriters Laboratories).
Old Standard (Units manufactured between October 1, 1995 and October 1,
1998) - First Generation CO detectors
|To a low level for a prolonged period
|Alarm after 30 days
|To a low level of CO for an extended
period of time
|Alarm within 90 minutes
|To a moderate level of CO for a
shorter period of time
|Alarm within 35
|To a high level of CO for a short
period of time
|Alarm within 15
New Standard (Units manufactured after October 1, 1998)
|To a low level for a prolonged period of time
|Alarm after 30 days
|To a low level of CO for an extended period of time
|Alarm within 189 minutes
|To a moderate level of CO for a shorter period of time
|Alarm within 50 minutes
|To a high level of CO for a short period of time
|Alarm within 15 minutes
The UL Standard was revised and any detector manufactured after October
1, 1998 must conform to the new Standard.
Also included in the new Standard is:
CO detector should ignore a CO level reading of 70 for at least 1 hour
CO detector should ignore a CO level reading of 150 for at least 10 minutes
Must only signal under alarm or trouble. No low-level warning signal
Must have a SILENCE button to shut it off. Must re-alarm after 6 minutes
if CO levels persist
Must meet the specificity test referencing non-alarm status at specific
concentrations of certain gases and vapors
To put levels into perspective:
|CO Level (ppm)
||Maximum outdoor air quality level as per EPA
||Maximum concentration for a continuous exposure in an 8-hour time period
||Headaches in 1 to 2 hours, life threatening after 3 hours
||Nausea and convulsions, death within 2 hours
||Nausea within 20 minutes, death within 1 hour
||Death within 1 to 3 minutes
Note: These studies are generally done on young, healthy people. These symptoms
can change drastically depending on age, sex, weight, habits (e.g.smoking),
and most importantly, your health.
Reliability of the detectors
CO detectors are supposed to alarm at certain levels as indicated in the
Recent testing suggests that many of these devices are not nearly as reliable
as they should be
CBC has provided television coverage that focused on false alarms and the
reliability of CO detectors
In 1994, Chicago was the first major city to make these detectors mandatory
in the living space
In the last three months of 1994, the Chicago Fire Department responded to
8,600 CO alarms
In almost every case there was no dangerous level of CO found during follow-up
Laboratory testing was done
Up to 1/3 of the alarms tested, failed to alarm
Technology for residential CO detectors is very primitive
Industrial detectors have a different set of standards and more sophisticated
technology. As a result, they are very expensive
Different detectors have large variances on the levels at which they are
supposed to alarm. The sensor technology used in home alarms is not designed
to measure and display low level, short term concentrations of CO. Substantial
differences exist in the sensitivity of different sensors at low levels.
As a result, they may go off too soon or not soon enough.
Standards require these devices to be tested at a humidity of 50%
Testing revealed that many devices failed to respond when humidity levels
were low even though they are supposed to work within a large humidity range.
See your CO detectors manual.
In Canada, humidity levels can fall well below 50% (in fact the humidity
should not be higher than 40%) during the cold season when furnaces and other
fuel burning appliances are in full operation
3. Effect of Other Gases and Vapors
Other gases such as Carbon Dioxide can also trigger a CO alarm. The UL 2034
Standard requires that CO alarms do not alarm when certain concentrations
of other gases and vapors exist in the vicinity of a CO detector. The level
for Carbon Dioxide in the old standard was low, which may have contributed
to many false alarms with first generation CO detectors.
CO detectors are designed to protect the average healthy human from death
or serious injury under the current standards; however –
People who are more susceptible cannot depend on these devices for total
protection. In this case, more sensitive CO detecting equipment should be
Several groups are working with UL to improve the standards. October 99 revisions
have already been drafted.
There is room for improvement by imposing stricter standards as well as technological
It is critical that people understand the dangers of CO and that the people
who investigate it are properly trained and are using CO testing equipment
Where to install a CO detector?
One or more CO detectors in accordance with the manufacturer’s recommendations.
Usually one per floor.
Maintain and test regularly as instructed by the manufacturer.
Things to look for when buying a CO detector?
How does all of this relate to your home inspection?
1) Type of sensor (electrochemical)
2) Certification-UL 2034
3) Conforms to new standard
4) IAS 6-96 is a supplementary standard to the UL 2034 which includes reliability
testing. This standard may not be visible on the box.
5) Other considerations include digital display, sensor life, power source,
A home inspection may reveal a potential Carbon Monoxide source.
Common deficiencies found during inspections include:
Damaged or rusted flue pipes
Dirty or blocked chimney flues
Cracked heat exchangers
Gas proofing deficiencies
Inadequate combustion air
Poorly installed equipment
There are other ways to test CO levels in a home.
These tests go beyond the scope of a standard home inspection.
Line drawings are from the Carson
Inspection Training Program and Home
Inspection Software Tool - Horizon