4717 Grand, Suite 820
Kansas City, Missouri 64112
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1021 E. Walnut
Springfield, Missouri 65806
(417) 866-8687
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TRIAL, August 1996, page 36

Family members from across the country gathered at the Andrews home in rural Missouri to celebrate Christmas 1992.1 After spending the day exchanging gifts and visiting with relatives, 10 family members retired for the evening. Around midnight, one young girl began to have trouble breathing. Her convulsions alarmed her parents, who rushed the girl to the hospital.

None of the others heard the commotion. They had been exposed to toxic levels of carbon monoxide. Of the seven people who remained at home sleeping, four never woke up. The other three were found comatose–saved by the young girl’s father, who had returned home in the wee hours and dragged them to safety.

After days of intensive hyperbaric oxygen therapy, the three injured family members slowly regained consciousness. Months of physical and cognitive therapy helped restore their ability to function, but only to a point. Their neuropsychological and physical deficits serve as a constant reminder of the fateful day carbon monoxide tragically affected their lives. The young girl was more fortunate. She made a complete recovery.

Plaintiffs’ lawyers representing victims of residential carbon monoxide poisoning face the difficult task of re-creating the circumstances of the exposure. Often the primary witnesses are dead or mentally impaired. This article discusses the nature of carbon monoxide and its effects, describes how to investigate the potential causes of exposure, and analyzes the responsibilities of the potential defendants.

Unintentional carbon monoxide poisoning kills an average of 2,700 people each year. About 1,150 of these deaths are not fire related.2 Thousands more people are injured. A Colorado study of 1,149 carbon monoxide poisonings between 1986 and 1991 found that 40 percent occurred at home.3 The highly publicized death of tennis star Vitas Gerulaitis by residential carbon monoxide poisoning in September 1994 also focused attention on this problem.4

Carbon monoxide is an insidious poison. It is colorless, odorless, and tasteless. Its presence is virtually impossible to detect. Because early symptoms of exposure mimic those of the flu, proper diagnosis and treatment of carbon monoxide poisoning can be delayed.

A minimal amount of carbon monoxide–a few parts per million (ppm)–is present in normal residential air. Carbon monoxide is also a by-product of the incomplete combustion of carbon-based fuels and is present in higher concentrations in exhaust gases and smoke.

The U.S. Environmental Protection Agency has set an ambient air quality standard for carbon monoxide at 35 ppm for one hour or 9 ppm for eight hours.5 The permissible exposure limit that has been set by the U.S. Occupational Safety and Health Administration is a time-weighted average of 50 ppm for an eight-hour workday.6

As the amount of carbon monoxide in the air increases, the risk of injury rises. The severity of injury depends on the concentration of carbon monoxide and the duration of exposure. Carbon monoxide induces toxic effects on the human body, primarily by tightly bonding to hemoglobin to form carboxyhemoglobin, which reduces the amount of oxygen the blood can carry. A nonsmoker will have a normal carboxyhemoglobin level of less than 2 percent, while smokers will have levels of 5 percent to 9 percent.7

Carbon monoxide concentrations of 100 ppm to 200 ppm can generate carboxyhemoglobin levels of approximately 10 percent to 20 percent, which trigger clinical symptoms such as headache, nausea, and mental impairment or confusion. Once the level reaches several hundred ppm, carboxyhemoglobin levels can reach approximately 30 percent to 60 percent. The effects on the human body at this level are profound–central nervous system damage, brain tissue damage from lack of oxygen, coma, and death.

Obtaining carboxyhemoglobin blood level results can help to diagnose carbon monoxide exposure, but a clinical evaluation of the victim’s symptoms is also essential. The difficulties in relying solely on carboxyhemoglobin levels are highlighted in a residential exposure case in Colorado.8

Two boys–11 and 12 years of age–were exposed to nearly identical levels of carbon monoxide from an idling car parked in their attached garage. Both boys were found unconscious in the basement. The 12-year-old’s carboxyhemoglobin level was 16 percent, while the 11-year-old’s was 12 percent.

By the time the boys were found, the 12-year-old was in acute distress. Despite successful resuscitation, he did not survive. The 11-year-old was comatose but regained consciousness after four weeks. After a pediatric rehabilitation program, he was able to return to school and resume daily activities.

Ironically, neither boy’s carboxyhemoglobin level reached the prescribed lethal level. One explanation for fluctuating levels of carboxyhemoglobin is that carbon monoxide has a half-life–the rate at which the body rids itself of one-half of the carbon monoxide in the blood stream–of four to six hours in normal room air. This is why many acute carbon monoxide poisoning victims are given emergency oxygen immediately. One hundred percent oxygen therapy reduces the half-life of carbon monoxide to one hour, greatly increasing the chances for recovery by lowering the carboxyhemoglobin level more quickly.

A person’s baseline hemoglobin, metabolism, and general health all influence susceptibility to carbon monoxide poisoning. These variances enable severe injury from acute exposure to toxic levels of carbon monoxide to occur even though the first blood sample drawn may show only a slightly elevated level of carboxyhemoglobin. Also, the delay between exposure and blood sampling as well as oxygen therapy administered during this period can account for a significantly reduced carboxyhemoglobin level.

By reviewing the carboxyhemoglobin level, the timing of the sample, and the extent of treatment, a toxicologist may provide useful evidence of the potential ranges of exposure times and concentration levels. Establishing those parameters can help pinpoint possible sources of carbon monoxide emission.

Locating the Emission Source

Plaintiffs’ lawyers must unravel the mystery of what caused the carbon monoxide emissions. Hiring a qualified expert to perform a detailed inspection of the residence is essential because the emission may have been the result of temporary conditions that no longer exist. Even when the cause of emission appears obvious, a thorough investigation will preclude the defendant’s attempts to deflect responsibility.

Because a number of factors may contribute to the carbon monoxide emission, it is essential for the investigating expert to have some familiarity with these types of cases. Once the initial evaluation is complete, the case may require multiple liability experts with qualifications in the areas of liquefied petroleum (LP) or natural gas distribution, gas appliance installation and operation, architecture and engineering of residences and residential heating systems, and toxicology. By using a variety of experts, plaintiffs’ attorneys can identify the source of the carbon monoxide and the responsible parties.

The most common sources of residential carbon monoxide exposures are oil, natural gas, or LP gas heating systems or appliances. Kerosene or other carbon fuel-burning space heaters are also potential hazards. The most common problem is a defect in the venting of exhaust gases that causes carbon monoxide to leak into the room. The presence of carbon monoxide depletes the quantity of oxygen in the air. As the oxygen-depleted air is utilized by the appliance as a source of combustion air, the burners operate more inefficiently, creating greater concentrations of carbon monoxide in the exhaust gases.

This vicious cycle–which often begins during the night while people are sleeping–can increase the carbon monoxide level to a toxic or even fatal level within a few hours.9 A plugged vent in an appliance, a disconnected exhaust flue, or a backdraft from a flue can cause carbon monoxide to build up. The only way to prevent it is to ensure adequate ventilation.

Weather conditions, efficiency of combustion, and adequacy of ventilation all play critical roles in the flow of exhaust gases. The following checklist will guide attorneys through the initial investigation. The plaintiffs’ attorney should determine each of these critical factors by consulting investigative reports of emergency personnel, interviewing witnesses, conducting on-site inspections, and initiating expert review.

  • Weather. Check the temperature, humidity, precipitation, and wind velocity and direction.
  • Residential exterior. Check the height and location of all flues and fireplace chimneys. Flue height can affect ventilation, and most codes–including the Uniform Building Code–specify minimum heights above roof lines. Inspect them from the top for blockages. Note any caps or wind guards and their position in relation to the roof or gables. They too can have an impact on adequate ventilation.

Look for fresh air sources, including vented eaves to the attic, dryer and basement vents, and exterior doors and windows. Eliminate alternative carbon monoxide sources, such as automobiles in the garage, by checking their ignitions and fuel tanks. Look for evidence of indoor use of charcoal briquettes, gas-fired generators, or other gas-fired power equipment.

Find out the names of the home’s architect and builder and locate plans and blueprints, if possible. Check the gas supply system, including the tank (for LP gas), the quantity of LP gas, and the status of the main valve and pressure regulators. Look at the vents on first- and second-stage regulators. Check and document settings and perform delivery and lockout pressure tests. These tests will determine the flow of gas to the appliances. Overpressurized flow can cause overfiring and produce excessive carbon monoxide. Inspect visible tubing and connections, and note manufacturers and date codes of regulators and components.

  • Residential interior. Check all interior doors, bathroom exhaust fans, thermostat settings, dryer vents, heating registers, and air return registers. These items all affect furnace operation and indoor air flow characteristics. Inspect all fireplace or wood stove operations and dampers and collect wood samples to ensure there was proper ventilation and to exclude any poisonous fumes from improper burning materials. Check smoke and carbon monoxide detectors as well as the heating system components for proper installation and operation.

Document the position of all exterior cabinet doors on forced-air gas furnaces. An ajar or mispositioned door can contribute to a backdraft of exhaust gases. Determine the manufacturer and date code of appliance regulators and furnaces. Check the pilot light, burner flames, air damper settings on burners, exhaust venting, and draft hood.

Note the dimensions of the furnace room and the sources of air transfer, such as a vented door. Identify the furnace installer and maintenance providers. Inspect the integrity of ductwork, noting any blocked distribution ducts, disconnected registers, and the condition of furnace filters. Retain the furnace filters if possible.

Check the air return cabinets and duct- work, heat exchanger, and combustion chamber. All other gas appliances should also be inspected. Use carbon monoxide detectors during the inspection in case the circumstances of emission still exist.

  • Injuries and deaths. Find out where inside the house the injured or deceased were found. Determine how long they were exposed to carbon monoxide and at what levels. Also find out how much time elapsed between the last exposure and the sample. Determine what symptoms the victims had exhibited and whether oxygen was administered.

Often, the physical conditions of the residence will have been inadvertently altered by police or rescue personnel. Statements from them concerning conditions at the time closest to the exposure are invaluable. Once the physical facts at the time of emission have been established, re-creation and testing with multiple carbon monoxide and temperature sensors–although costly–may be justified, provided there are significant damages.

Identifying Defendants

The results of the factual investigation must be compared with applicable regulations and codes to identify breaches of legal duties. Claims of negligence, failure to warn, strict liability, and breach of warranty may apply to a number of parties. The following section outlines the standards governing the potential defendants in a carbon monoxide case.

Fuel suppliers. The National Fire Protection Association’s (NFPA) Code 58 governs the storage and handling of LP gases.10 Adjustment of LP appliances, tanks, tubing, and regulators as well as delivery procedures for LP gas must comply with this code.

Natural and LP gas suppliers must also comply with the National Fuel Gas Code (NFPA 54), which regulates the venting of exhaust gases as well as the pressure testing and inspection of existing systems.11

Code violations can provide a solid foundation for negligence claims. A claim of negligence per se may even be supported in jurisdictions that equate these codes with statutory requirements.

National and statewide industry associations also produce training materials that set the industry standard. For example, the National Propane Gas Association sponsors the Gas Check Program, which details out-of-gas procedures and system inspections. Most states also require an internal procedure manual and training requirements for gas delivery employees. Often, these manuals incorporate large parts of the NFPA codes, so their discovery is essential.

Builders and architects. The Uniform Building Code and the Uniform Mechanical Code set the dimensions and locations for roof vents. NFPA Code 54 sets dimension criteria for furnace rooms to ensure adequate air for combustion and positive ventilation pressure. Failure to meet these codes may result in a backdraft of exhaust gases containing lethal levels of carbon monoxide.

Installers and maintenance providers. Those installing gas appliances must also comply with NFPA Code 54, especially regarding equipment ventilation, operation, and modification from natural to LP gas. In particular, code provisions detail venting of equipment, installation and testing procedures, and the modifications of existing appliance installations. In addition, the duty to review the system functions and to inspect for human error is a fertile area of liability. The American Society of Heating, Refrigeration, and Air-Conditioning Engineers has promulgated standards outlining the requirements for proper installation.

Furnace manufacturers. The American National Standards Institute (ANSI) has promulgated Standard Z21.47, which governs the vast majority of gas-fired heating appliances.12

This standard currently requires a vent safety shut-off switch that detects flue reversals. A flame roll-out switch is also required to prevent burning outside the heat exchanger. Either of these switches may avert a potential carbon monoxide emission by automatically shutting off the furnace.

The furnace doors covering the blower compartment must be securely in place. If they do not fit tightly or have been removed, negative pressure can develop within the furnace room that may lead to a backdraft of exhaust gases when the blower engages. To prevent this, ANSI requires an interlock switch that prevents the furnace from firing if the doors are ajar.

Furnaces manufactured without these devices–including those that predate the code requirement–are defective and unreasonably dangerous. The minutes of the Gas Appliances Manufacturers Association meetings provide valuable insight into the industry’s awareness of the risks of carbon monoxide exposure and the efforts of consumer safety proponents to require safety measures.

A careful inspection of the furnace’s heat exchanger should also be performed. The heat exchanger is the metal barrier between the combustion compartment–which contains exhaust gases–and the flow of distribution air. In addition to transferring heat, the heat exchanger should prevent exhaust gases from mixing with the distribution air.

Many times, a cracked heat exchanger will be a suspected cause of emission problems. The mistaken belief is that exhaust gases will migrate through the cracks into the heated distribution air, which is distributed throughout the home via the ductwork. However, since cracks in the heat exchanger normally occur in areas of positive pressure, the exchanger is at most a minor contributor to the emission problem.13 This is because cracks can allow air to blow against the burners, reducing the efficiency of combustion and leading to a higher level of carbon monoxide in the exhaust gases.

Detector manufacturers. Carbon monoxide detectors do not necessarily prevent injury.

If detectors are present, they should be carefully inspected for possible malfunction. They should also comply with the Underwriters Laboratory Standard 2034.

Certain detector failures are well documented. For example, the Consumer Product Safety Commission has issued warnings about the potential failure of the SC-01 Accu sniffer detector, imported and distributed by Sinostone Corp. of Wood Dale, Illinois.14

With technological advances in detectors and their increased affordability, however, more and more tragedies are being avoided. But detection of carbon monoxide exposure is no substitute for its prevention by those who profit from the purchase and the continued use of gas or oil-fueled heating systems and appliances.

With thorough investigation and testing, counsel for those who have been poisoned by carbon monoxide can identify the responsible parties and prove their negligence. Only then can the “silent killer” be brought to justice.


1. The name of the family has been changed.

2. Nathaniel Cobb & Ruth Etzel, Unintentional Carbon Monoxide Related Deaths in the United States, 1979 Through 1988, 266 JAMA 659 (1991).

3. Magdalena Cook et al., Unintentional Carbon Monoxide Poisoning in Colorado, 1986 Through 1991, 85 AM. J. PUB. HEALTH 989 (1995).

4. See generally Noel Cohen, Star’s Death Highlights CO Risks; But No Major Response Ensues, LEADER’S PROD. LIAB. L. & STRATEGY, Oct. 1994, at 5.


6. 29 C.F.R. 1910.1000 (1996).

7. Unintentional Carbon Monoxide Poisonings in Residential Settings–Connecticut, November 1993-March 1994, 44 MORBIDITY & MORTALITY WKLY. REP. 765 (1995).

8. M. Cook et al., Carbon Monoxide Poisoning–Weld County, Colorado, 1993, 272 JAMA 1489 (1994).

9. W. Alan Bullerdiek & D.E. Adams, Investigation of Safety Standards for Flame-Fired Furnaces, Hot Water Heaters, Clothes Dryers, and Ranges (July 1975) (unpublished report prepared for the Consumer Product Safety Commission).





14. Consumer Warning: CPSC Issues Press Release on Potential Risk Associated with 18,700 Sinostone Detectors, Prod. Safety & Liab. Rep. (BNA) No. 24, at 81 (Jan. 26, 1996).