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.
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.
Solid fuels, such as wood, always produce carbon monoxide when they are burned. Gas and liquid fuels may produce no CO or very little.
Background
• New technology
• Introduced in the early 1990’s
• Designed to warn homeowners when CO reaches dangerous levels within the home
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:
Residential
• Biometric (Oldest type of sensor)
• Metal Oxide Semi-conductor
• Electrochemical (The best of the three types for a residential sensor)
Industrial
• 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 levels or standards are set by UL (Underwriters Laboratories).
Old Standard (Units manufactured between October 1, 1995 and October 1, 1998) - First Generation CO detectors
|
Exposure
|
CO (ppm)
|
Time
|
| To a low level for a prolonged period of time |
15
|
Alarm after 30 days |
| To a low level of CO for an extended period of time |
100
|
Alarm within 90 minutes |
| To a moderate level of CO for a shorter period of time |
200
|
Alarm within 35 minutes |
| To a high level of CO for a short period of time |
400
|
Alarm within 15 minutes |
New Standard (Units manufactured after October 1, 1998)
|
Exposure
|
CO (ppm)
|
Time
|
| To a low level for a prolonged period of time |
30
|
Alarm after 30 days |
| To a low level of CO for an extended period of time |
70
|
Alarm within 189 minutes |
| To a moderate level of CO for a shorter period of time |
150
|
Alarm within 50 minutes |
| To a high level of CO for a short period of time |
400
|
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 without alarming
• CO detector should ignore a CO level reading of 150 for at least 10 minutes without alarming
• Must only signal under alarm or trouble. No low-level warning signal is allowed
• 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)
|
Health Effect
|
| 0 |
Desirable level |
| 9 |
Maximum outdoor air quality level as per EPA |
| 50 |
Maximum concentration for a continuous exposure in an 8-hour time period (OSHA standard) |
| 400 |
Headaches in 1 to 2 hours, life threatening after 3 hours |
| 800 |
Nausea and convulsions, death within 2 hours |
| 1600 |
Nausea within 20 minutes, death within 1 hour |
| 12,800 |
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.
The Controversy
• Reliability of the detectors
The Issue
• CO detectors are supposed to alarm at certain levels as indicated in the tables above
• 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
Example
• 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 investigations
Result
• Laboratory testing was done
• Up to 1/3 of the alarms tested, failed to alarm
Reasons
1. Technology
• 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.
2. Humidity
• 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.
Conclusions
• 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 used.
• 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 development.
• 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 properly.
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?
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, and warranty.
How does all of this relate to your home inspection?
A home inspection may reveal a potential Carbon Monoxide source.
Common deficiencies found during inspections include:
• Venting deficiencies
• Damaged or rusted flue pipes
• Dirty or blocked chimney flues
• Cracked heat exchangers
• Gas proofing deficiencies
• Inadequate combustion air
• Poorly installed equipment
Limitations –
• Visual Inspection
• Equipment available
There are other ways to test CO levels in a home. These tests go beyond the scope of a standard home inspection.