WHAT IS CARBON MONOXIDE?

Carbon monoxide is frequently referred to as the “Silent Killer”.  CO is colorless, odorless, tasteless, and very deadly.  Because it cannot be detected by human senses, it can kill you without warning.  According to the Journal of the American Medical Association (JAMA) at least 1,500 people are killed, and at least 10,000 more are forced to seek medical attention every year because of exposure to this dangerous contaminant.  Because the symptoms associated with CO poisoning frequently mimics those of other medical conditions, most investigators feel the true number of CO poisonings per year is even higher.  In any case, CO causes more accidental poisoning than any other chemical substance.

CO is produced by incomplete combustion.  That means any combustion process can be a source of CO.  CO is especially associated with exhaust of internal combustion engines and heating systems in which fuel is burned to produce heat.  Faulty or poorly maintained furnaces and heaters are a leading cause of indoor CO buildup.  Other sources include cigarette smoke, automobile exhaust, wood stoves and fireplaces, dirty or plugged chimneys, gasoline lawnmowers or blowers, propane or gasoline operated forklifts, or other power machinery, as well as many other gas, oil, or kerosene powered appliances.  Inadequate ventilation is a major contributor to CO buildup, especially in the winter.  Residences and buildings are tightly sealed against the cold and heaters and furnaces are in constant operation.  Often, additional fresh air is all that is required to dissipate low-level CO buildup.

Unfortunately, unless you have a carbon monoxide monitor to tell you when a problem has occurred, you’ll never know when you’re getting into trouble.
 
 

WHY IS CARBON MONOXIDE SO DANGEROUS?

It’s the hemoglobin molecules in our red blood cells that form the bonds, which allow red blood cells to transport oxygen.  Unfortunately, hemoglobin is also able to form bonds with carbon monoxide.  In fact the bonds that are formed between hemoglobin and carbon monoxide are over 200 times stronger than the bonds that are formed between hemoglobin and oxygen.  Red blood cells that have been contaminated with carbon monoxide can’t transport oxygen.  In effect you suffocate “from the inside out”.  Because these bonds are so strong they take a long time to break down.  The carbon monoxide molecules tend to remain attached and even low concentrations of CO in the air can lead over time to dangerously high concentrations in the blood.  That's what makes chronic exposure at even low levels so harmful.
 
 

WHAT ARE SOME CHARACTERISTICS OF CARBON MONOXIDE?

Carbon monoxide is colorless, odorless, about the same weight as air, and very toxic.  The symptoms of CO poisoning mimic those of many other medical conditions.  The symptoms include headaches, fatigue, nausea and other “flu-like” symptoms, as well as (with higher exposure) loss of consciousness, coma, and death.  A concentration of only a few thousand parts-per-million can be quickly fatal.  CO can also exacerbate or worsen preexisting medical conditions such as heart disease.  Firefighters are particularly at risk.  The NFPA has documented numerous cases of firefighters who have experienced fatal heart attacks as a direct consequence on an underlying medical condition.
 
 

HOW MUCH IS TOO MUCH?

The answer depends on which standard you look at.  Workplace rules for CO exposure are very tight and are getting tighter.  Exposure limits for Federal or State Occupational Safety and Health Administration (OSHA) “Permissible Exposure Limits” regulate most industrial workers.  Current (1996) Federal OSHA rules specify a maximum concentration (calculated as an 8-hour TWA) of 50 ppm.  Many states specify a more conservative two part PEL which consist of an 8-hour TWA of 35 ppm, with a Ceiling (instantaneous maximum) exposure limit of 200 ppm.

When it comes to residential exposure, the guidelines are not quite as clear cut.  Home CO detectors which have been listed by Underwriters Laboratories as Compliant with Standard 2034 for Residential CO Detectors are designed to go into alarm within 15 minutes when CO=400 ppm, within 35 minutes when CO=200 ppm, within 90 minutes when CO CO=100 ppm, and within 8 hours when CO =15 ppm.  Of course, whatever the times and concentration involved, when a CO alarm goes off, it’s usually the local Fire Department that responds to the situation.
 
 

HOW DO THE CO MONITORS USED BY THE FIRE DEPARTMENTS WORK?

Gas detectors used by the Fire Departments to respond to CO alarms need to be durable, easy to use, provide accurate numerical readings and respond quickly to changes in CO concentration.  The instruments most commonly used by Fire Departments use substance-specific, electrochemical sensors for the direct measurement of CO.  Substance-specific sensors are used because they are compact, require little power to operate, and show very little response to other contaminants that may be present.  This is a very important point.  If the sensor that you’re using to measure CO is also responsive to perfume, hair spray, or other harmless contaminants that may be present, you can’t depend on your readings.  (The fact that some home CO detectors do respond to contaminants other than CO is a major source of false alarms).

Finally, it had better be easy to quickly verify the accuracy of the detector.  The readings used for the health and safety evaluations of this kind have to be accurate.  Instruments, which are capable of automatic calibration adjustments, are highly desirable for this reason.  The instruments used in the fire service has to live up to these requirements.  It’s a tall order, but instrument manufacturers are increasingly up to the job.
 
 
 

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