Safety This Carbon Monoxide Season

By Jay Freeman, MS, PE, CFEI


According to the Consumer Product Safety Commission, an average of 170 people die each year from carbon monoxide from non-automotive consumer products.  These include gas-fired appliances, such as furnaces, water heaters and room heaters.  Also included in this group is  engine-powered equipment such as portable generators.  Generators account for 30 to 80 deaths per year.  There are also incidents of deaths from automobiles left running in garages.

THIS IS IMPORTANT.  Carbon monoxide is odorless, colorless and tasteless.  CO detectors save lives.  Colorado requires them.  They are inexpensive and readily available.  If you have gas appliances or an attached garage install several for your dwelling.

Cases involving carbon monoxide exposures can bring large verdicts.  As an example, in a hotel in Baltimore, 20+ workers at a Ruth’s Chris steakhouse were awarded over $34 million by a jury in a trial in 2010.

Carbon Monoxide Basics

Virtually all equipment that burns hydrocarbon fuels, such as gasoline, propane, and natural gas, produces some carbon monoxide in the pic1_01.2015_AdvThinkingcombustion products or flue gas.  Internal combustion engines on portable equipment, such as generators and lawnmowers, produce fairly high levels of carbon monoxide, potentially in the range of 30,000 to 50,000 parts per million (ppm).  Automobiles with new emission control systems may only produce 100 ppm in the exhaust.  Gas burning appliances such as furnaces and water heaters typically only produce about 100 ppm of carbon monoxide in the flue gas.  The ovens in gas ranges may produce several hundred parts per million of carbon monoxide in the flue gases.  Because of the small size of the burner on an oven, the net quantity of carbon monoxide from a gas range flowing into a dwelling produces very low levels of CO.

Five Main Factors in Carbon Monoxide Incidents

  1. The appliance, such as from a gas furnace or water heater, must be running poorly and producing high levels of carbon monoxide in the flue gas.
  1. Some, or all, of the flue gas must be prevented from going up the flue or chimney and spill into the dwelling.
  1. The flue gases must have some means to be distributed throughout the house where the occupants are located.
  1. The appliance must be running long enough, such as a furnace in cold weather, to continue to dump carbon monoxide into the dwelling.
  1. The occupants must be exposed to the levels of carbon monoxide long enough to cause ill effects.

So what makes appliance run poorly?  Putting too much fuel and not enough air in an appliance or too little air for the fuel that’s going in will produce increased levels of carbon monoxide.  This is similar to leaving the choke in the “on” position on something like a lawnmower or a snow blower.  It runs poorly, produces black smoke and a tremendous amount of carbon monoxide.

Improper or no maintenance, or general degradation of a gas appliance, such as a corroded heat exchanger, can cause an appliance to run poorly.  More frequently, incidents occur because the appliance is not properly set up during installation.  Many of the new appliances require sophisticated equipment to properly “tune” the appliance when it is installed.  Appliances at higher elevations require adjustment to reduce the amount of fuel going into the appliance.

Another problem occurs when an appliance is purchased for natural gas and is operated on propane.  Propane has about 2½ times the heating value in a cubic foot of gas compared to natural gas.  This can cause extremely high levels of carbon monoxide.  Levels as high as 176,000 ppm carbon monoxide in flue gas have been observed with appliances that are not properly converted from natural gas to propane.

As long as the flue gases from the appliance leave the dwelling by going out the vent pipe or chimney, the likelihood of a carbon monoxide problem is small.  If the flue or chimney should be compromised and separated, or should become blocked, there is the potential for combustion products to enter the dwelling.

Once the combustion products enter the dwelling, they invariably will distribute throughout the dwelling. The rate of this distribution can be drastically increased if there are return air openings on a forced air furnace where the flue gases spill.  It should be pointed out that carbon monoxide has about the same density of air.  Because the combustion products are hotter than the room air, combustion products will tend to rise within a dwelling.

Appliances, such as water heaters, being used for domestic hot water, usually run only about an hour to completely reheat a tank of water.  Typically this is not enough time to cause a problem even if the flue gases are dumping into the dwelling.  Furnaces, however, run longer in cold weather.  It is a well known fact that many more carbon monoxide poisonings occur in the winter when houses are sealed up and the heating appliances are running longer.

Last, but not least, the individuals in the dwelling have to be exposed to high levels of carbon monoxide levels for an extended period of time.  Carbon monoxide in the air does not immediately become absorbed in the blood.  The blood, however, does have an affinity for carbon monoxide that is about 200 times that of oxygen.  The carbon monoxide level (percentage) in the blood builds up over time to a maximum or equilibrium level during the exposure, which is based on the concentration of carbon monoxide in the air that is breathed.  Lethal levels for a person not in excellent shape might be as low as 400 ppm in air for an exposure time of four hours.

Many of the symptoms of carbon monoxide are similar to those of the flu.  These include headache, fatigue, shortness of  breath, nausea, and dizziness.  Higher levels of carbon monoxide, and consequently higher carboxyhemoglobin levels in the blood, can cause mental confusion, vomiting, loss of consciousness and death.  Carbon monoxide basically displaces the oxygen in the blood and starves the organs in the body, such as the brain and heart, of oxygen.  This can cause brain damage or heart attacks.

It should be pointed out that the uptake of carbon monoxide can be fairly rapid but it is difficult to get the carbon monoxide out of the blood.  If an individual is breathing fresh air to get rid of carbon monoxide, the half-life is about five hours.  Breathing 100% oxygen reduces the time to about 80 minutes and hyperbaric treatment produces a half-life of about 25 minutes.

Standards for Carbon Monoxide

Just as there are standards for the amount of carbon monoxide produced by an appliance, there are acceptable exposure levels of carbon monoxide and exposure times for individuals.  OSHA allows a 50 ppm exposure of carbon monoxide for eight hours per day, 40 hours per week in the workplace.  In an average person this would increase the carbon monoxide levels in their blood to a little over 6% carboxyhemoglobin.  EPA National Ambient Air Quality Standards for carbon monoxide in outside air are no more than 9 ppm once per year.

Things To Do If There Is A CO Incident:

Preserve the evidence.  Many times repairs are made to get heat in the dwelling by replacing the furnace and the original/faulty furnace is tossed.

If possible, obtain carbon monoxide readings in the dwelling.  Take lots of photographs and document any changes that are made to the system or appliance.

Talk to an expert as soon as possible.  Get someone knowledgeable on-site ASAP.

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