Why You Need a Carbon Monoxide Detector

What Carbon Monoxide is and Why You Need a Detector

Carbon Monoxide (CO) 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 CO gas. Examples of CO producing devices commonly in use around the home include:

  • Automobiles
  • Charcoal grills
  • Fireplaces and woodstoves
  • Fuel fired furnaces (non-electric)
  • Gas dryers
  • Gas stoves
  • Gas water heaters

Injuries and Deaths Caused

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.

Medical Effects of CO and How to Recognize Them

CO 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.

Concentration and Symptoms

The following table describes the symptoms associated with a given concentration of CO:

Percent CO2
Symptoms and Medical Consequences
10%No symptoms (Heavy smokers can have as much as 9% CO)
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)

Symptoms of Concentration Levels

Since one can't easily measure CO 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 COTimeSymptoms
35 PPM8 hoursMaximum exposure allowed by OSHA in the workplace over an eight hour period
200 PPM2-3 hoursMild headache, fatigue, nausea and dizziness
400 PPM1-2 hoursSerious headache- other symptoms intensify (Life threatening after 3 hours)
800 PPM45 minutesDizziness, nausea and convulsions(Unconscious within 2 hours, death within 2-3 hours)
1,600 PPM20 minutesHeadache, dizziness and nausea (Death within 1 hour)
3,200 PPM5-10 minutesHeadache, dizziness and nausea (Death within 1 hour)
6,400 PPM1-2 minutesHeadache, dizziness and nausea (Death within 25-30 minutes)
12,800 PPM1-3 minutesDeath

Symptom Confusion

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 1 recurrent theme that is most significant in the recognition of CO 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 CO these symptoms are the best indicator that a potentially serious buildup of CO exists. This comment will be returned to later.

Types of CO Detectors and How They Work

There are a number of different types and brands of CO 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 CO gas.

Selecting the Best Detector for You

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 CO 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. Detectors with built-in digital readouts seem to be the most reliable.

How Many CO Detectors to Have and Where to 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, CO 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.

Most Common Causes of CO Detector Alarms

There are many conditions which can cause a CO 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:

CausePreventive Action
Inadequate fresh air venting of the homeHave a heating contractor install afresh air makeup system in the home
Running gas powered equipment or automobiles in a home or garageGas powered equipment or vehicles 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 garageCharcoal grilling is a tremendous producer of CO gas (Charcoal grills should never be operated in the home)
Malfunctioning appliances or equipment in the homeAll fuel burning appliances or 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 alarmBuy only UL Listed alarms conforming to the latest revision (June 1995) of UL standard 2034 (This revision includes new requirements to minimize nuisance alarms)

Unpredictable Causes

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.

How to Respond When Your CO Detector Goes Off

First and foremost, stay calm. As mentioned previously most situations resulting in activation of a CO 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 CO gas. The best initial treatment for CO 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.

Important Information

Remember, CO is produced as a by-product of combustion. Unless you have fuel burning (non-electric) equipment running you cannot have CO. Unfortunately there are a lot of unreliable CO detectors out there. If your detector is over 5 years old, it may need replacing. If you are still unsure, call 911 and the Bellaire Fire Department will bring out their own CO monitoring equipment.