Carbon monoxide (CO) has been called the “silent killer” because its victims are normally unaware that they have been poisoned.  Many times this silent killer will strike when the victims are asleep and helpless to react.

 

Carbon monoxide is a colorless, odorless, toxic gas.  While there are many sources for carbon monoxide, it is often produced in gas burning appliances by the incomplete combustion of a carbon-based fuel, such as natural gas or propane.  Wood burning fireplaces are also a source of carbon monoxide.

 

Gas appliances are design and performance certified by the American Gas Association (AGA) using national standards developed by the American National Standards Institute (ANSI.)  For example, gas fired central furnaces are certified under ANSI Z21.47 - 1993 to produce carbon monoxide levels less than 400 parts per million (PPM) in an air free sample of the flue gases when tested in an atmosphere having a normal oxygen supply.   While national testing standards allow some amounts of carbon monoxide, most gas appliances when installed in accordance with national and local codes and properly maintained will produce only trace amounts of carbon monoxide (normally less than 50 PPM.)

 

Gas appliances that have been correctly installed and properly maintained combine fuel and oxygen contained in air to produce products of complete combustion consisting of water vapor, carbon dioxide and nitrogen.  If the gas appliance has not been properly installed or maintained the combustion process can be impaired resulting in incomplete combustion of the fuel.  When this occurs the products of incomplete combustion are water vapor, carbon dioxide, nitrogen, carbon monoxide and almost always a compound called aldehyde.  While carbon monoxide is odorless, aldehydes have a sharp, penetrating odor and can be detected by smell at very low concentrations.  The absence of aldehydes does not assure that carbon monoxide is not present.  However, if the odor of aldehydes is present then it is almost certain that carbon monoxide is also present.

 

Products of combustion (complete or incomplete) are carried to the outside atmosphere through the appliance venting system.  As long as the venting system is intact and operating properly, any carbon monoxide produced by the gas appliance will be vented to the outside with no ill effects on the building occupants.  If the vent system should fail for some reason, or if the gas appliance is not vented properly, excessive levels of carbon monoxide accompanied by high levels of water vapor and possible aldehydes could accumulate in the area around the gas appliance and possibly be circulated to other parts of the occupied spaces.  

 

Symptoms of carbon monoxide exposure at lower concentrations in healthy people include headaches, decreased alertness, dizziness, flu-like symptoms, nausea, fatigue, rapid breathing, confusion, disorientation, impaired judgment and weakness. Symptoms of carbon monoxide exposure at higher concentrations include brain damage, coma and death.

 

The effects of carbon monoxide poisoning depend on the concentration of carbon monoxide inhaled, the duration of the exposure and the individual's activity level and health status.  Inhaled carbon monoxide is absorbed into the blood and combines with hemoglobin to a much greater extent than oxygen.  Carbon monoxide remains in the blood longer than oxygen.  Commonly, carbon monoxide health effects are considered in terms of the percentage of carbon monoxide in the blood's hemoglobin that is expressed as percent carboxyhemoglobin (% COHb.)  In the average nonsmoker, COHb is 1.5% or less (0.7% due to metabolism) while heavy smokers' COHb may be as high as 10%.

 

Inhaling air containing 400 PPM carbon monoxide for periods of time in excess of three (3) to four (4) hours can result in COHb levels of 35% to 40% and be life-threatening.  Inhaling air containing 800 PPM carbon monoxide for periods of time in excess of two (2) to three (3) hours can result in COHb levels of 50% to 60% and result in death.  Inhaling air containing 1,600 PPM carbon monoxide can result in death within one (1) hour.

 

The Consumer Products Safety Commission (Carbon monoxide fact sheet, publication #466) has estimated that as recently as 1989 there were about 220 deaths each year resulting from carbon monoxide poisoning associated with faulty gas appliances.  The CPSC also estimates that as many as 5,000 people are treated in emergency rooms for carbon monoxide poisoning each year.  However, this estimate is believed to be an underestimate because many people with carbon monoxide poisoning mistake their symptoms for the flu or are misdiagnosed and never treated. 

 

In cases classified as accidental death, it may or may not be evident that carbon monoxide poisoning was the cause.  However, even in those cases where it is obvious from the beginning that carbon monoxide poisoning was the cause of death, it may not be as obvious as to what the root cause or source of the carbon monoxide poisoning was.  Many times police and fire investigators, and sometimes even well trained heating experts, base a conclusion on an obvious observable factor while missing the root cause of the accident.  Most of the time, in carbon monoxide accidents involving gas appliances, there are a number of factors that contribute to the cause.  Many of these factors may have been present for a number of years before an actual death has occurred.

 

When investigating the carbon monoxide accident it is important to think of the gas appliance as only part of the overall heating system.  The components of the heating system include:

 

·       The fuel supply

·       The gas appliance

·       The combustion and ventilation air supply

·       The venting system

·       The operation and maintenance personnel (including the owner, heating equipment repair personnel and the fuel supplier)

 

Because of the safety design of modern gas burning appliances certified by the AGA, most carbon monoxide accidents involve failures in two (2) or more of the heating system components. One failure to cause the appliance to produce carbon monoxide and a second failure to cause the carbon monoxide to be collected or circulated in a living or sleeping area.

 

A malfunction in any one of the components of the heating system could cause the appliance to produce carbon monoxide.  When this happens, the appliance may seem to still operate in a safe manner because the carbon monoxide is being vented to the outside atmosphere through the venting system.  However, if the venting system should fail for some reason or if a second malfunction should occur (ie. faulty heat exchanger), dangerous levels of carbon monoxide could be circulated to occupied areas of the structure.

 

Besides the obvious causes of failure, other less obvious causes are faulty installations, insufficient combustion air supply, poorly maintained heating system components and sometimes poorly designed features within the appliance itself.  Many times a deteriorating condition is noticeable before a serious failure occurs.  Rusted and discolored vent pipes, odors, unexplained gas pilot outages, water vapors condensing on windows during cold periods and complaints of poor heating are all indicators of a malfunctioning heating system which, if left uncorrected, could result in a carbon monoxide poisoning.

 

As stated earlier not all carbon monoxide cases are obvious from the beginning.  Many times the people who first respond to an accident disturb key evidence while evaluating the scene and attempting to make the location safe.  Typical actions taken by response personnel include moving boxes or furniture that may be blocking combustion air openings and removing panels from gas fired appliances to shut off the gas.  In order to minimize any destruction of key evidence it is imperative that a qualified expert who specializes in forensic investigations be contacted and allowed to inspect the site as soon as possible.

 

When investigating the carbon monoxide accident the following factors must be evaluated before a probable root cause can be determined. Extensive photographs and videotaping of the scene should be completed to document the conditions as found.  Every effort should be made to preserve key evidence for evaluation.  The conditions as found (initial discovery) must not be changed or corrected until the investigation is completed.  In most cases the gas appliance and venting system components should be removed after the follow up inspection and investigation and preserved as evidence.

 

While it is preferred that a forensic expert be involved from the initial discovery through the completion of the investigation, this is normally not the case.  What normally occurs is the forensic expert is called in at some point after the initial discovery and investigation is completed.  From a forensic viewpoint it is important to involve an expert, at least on a consulting basis, as soon as possible after the incident.

 

INITIAL DISCOVERY AND INVESTIGATION

 

·       First discovery – Who discovered the victim?  How did they discover the victim?  What happened to cause them to find the victim?

 

·       Ambient conditions in the space as found – What were the conditions when the victim was first discovered?  Was the room cool, warm or hot?  Was there water moisture on the windows?  Was there an odor in the room and if so what did it smell like?

 

·       First response – Who responded?  What did the police and fire departments find?  Did the local building code department respond?  Did the local gas supplier or gas utility respond?  Did they take photographs?  What conditions did they find?   Did they turn off the appliance?  If so, how?  Were any tests conducted on the appliances?  Did they prepare a report?  What conclusions did they reach?

 

·       Make safe – Did the local authorities call in someone to inspect the gas appliances to make them safe?  Was the building evacuated?  If so, why?  What actions were taken to make the building safe?  Was the suspect gas appliance repaired or altered after the incident?  If so, how and by whom?

 

FOLLOW UP INSPECTIONS AND INVESTIGATION

 

·       Weather data – What were the local weather conditions preceding the incident?  Outside temperature patterns, wind speed and direction, snow cover, rain, sleet, etc. all may have a bearing on the operation of the venting system and combustion air and ventilation system. Weather data should be collected from local sources such as the state university and local newspapers.

 

·       Building orientation and construction – What direction is the building facing?  Make a sketch of the building and rooms showing location of the victims, heating appliances, other gas burning appliances, fireplaces and other air consuming devices such as exhaust fans and exhaust hoods.  Record all dimensions, including ceiling height and window and door locations.

 

Note the age of the construction and construction type (frame, brick, etc.) and the tightness of the building (weather stripped, caulked, etc.) Mark locations of gas vents and sources of combustion air including size and type of air grilles and air louvers.

 

·       Overall condition and appearance of the building and gas appliances – Does it appear that the building and appliances are in good repair?  Is there an existing hazardous condition?  Is there a hazard tag on the gas appliance?  If so, when was it placed and by who?  What action is recommended to correct the hazard?

 

·       Maintenance history – Have there been any previous problems reported?  What types of repairs have been completed in the past?  When were the problems reported and when were the repairs completed?  Who discovered the problems and who made the repairs?

 

·       Evaluate appliance installation – Is the appliance installed in compliance with the manufacturer’s installation instructions?  Does the installation comply with national standards (NFPA 54) and local building codes?  Record locations of fuel lines, gas pressure regulators including gas pressure regulator vent lines and propane tanks if fired on propane.

 

Sketch the existing appliance installation and venting system indicating sources of combustion and ventilation air and any other information which may be pertinent to the operation of the appliance.  Note the condition of the appliance and venting system.

 

·       Collect appliance data – Record all name plate data for all appliances.  Include serial numbers and model numbers on all automatic gas control valves.  Also note any special devices or controls that may be installed on the appliances.  Examples of special devices may include automatic vent dampers, heat reclaimers and other retrofitted energy conservation devices.

 

·       Run combustion tests – Test the gas appliance(s) to determine what their normal operating characteristics are.  Test all gas appliances in the structure. Repeat all tests under different conditions to duplicate conditions that existed at the time of the incident.  At a minimum test for carbon monoxide at the flue outlet (inlet to draft diverter) and measure stack temperature.  Also it may be necessary to measure oxygen or carbon dioxide content.  Note burner ignition and operating characteristics (yellow tip, blue flame, primary air adjustments, etc.)

 

Ambient carbon monoxide levels in the appliance area, as well as in the area where the victim was found, should be monitored.

 

·       Measure the fuel input rate – Is the appliance properly adjusted for the elevation?  The name plate rating for AGA certified appliances must be derated at the rate of 4% for each 1,000 feet in elevation.  The actual heat (fuel) input should be determined and recorded.  For propane fired appliances it is necessary to measure the burner orifice sizes and compute the actual input.  For natural gas fired appliances it is necessary to measure the actual input by “clocking” the gas meter.  It is necessary to contact the local gas utility for actual heating (BTU) and specific gravity values.

 

·       Miscellaneous factors – Are there any other factors or conditions that might have a bearing on the cause of this incidence?  Such factors may include faulty maintenance by a third party or failure of a third party to provide a warning when they had knowledge of a hazardous condition.

 

DETERMINE CAUSE(S)

 

Although the cause of the incident may seem obvious at first, don’t jump to early conclusions.  Only after all of the items and information discussed above have been collected and analyzed is it possible to determine the root cause or causes of the carbon monoxide poisoning.  As I stated earlier, with modern gas fired appliances there are usually two or more failures that finally result in a tragic accident.

 

Two common causes of carbon monoxide accidents are failures of the venting system resulting from insufficient combustion air and faulty installations.  Other causes include maladjusted gas burners, problems resulting from poor maintenance, failed appliance components (heat exchangers), incorrect gas input caused by problems with the gas supply, interference from other appliances (fire places, other appliances sharing a common vent) and internal failures of gas appliance component parts due to faulty design.

 

The key is to collect as much data as soon after the incident as possible and evaluate that data to reach a determination of probable cause.