This case study summarizes a matter in which a group of campers were overcome by
carbon monoxide poisoning. It illustrates the importance of taking the initiative
to acquire necessary objective evidence to refute presumptions through a scientifically
credible toxicological assessment.
A group of campers attending an event at the height of summer stayed in a rented
trailer in an open field adjacent to other campers. A rented portable generator
provided AC power. Initially set a reasonable distance away from the trailer, the
generator was moved directly next to the trailer sometime during the early morning
hours. Later that morning, all inside were found dead.
Families of the victims filed a high-dollar lawsuit naming multiple defendants.
Specifically, the plaintiffs' alleged that the generator rental company failed to
provide training and documentation regarding use of the generator. They further
alleged that the generator itself was defective and caused or contributed to the
fatalities. Finally, they contended that the failure of the trailer rental organization
to provide a working carbon monoxide detector constituted fault in the matter. Defendants
argued that the rental agreement precluded claims for liability and that they were
not accountable for the generator warning labels.
Confronted with emotionally-charged litigation and minimal unbiased evidence, defendants
retained Dr. Sawyer to conduct an independent investigation and produce an objective
Dr. Sawyer reviewed police, fire department and medical examiner reports, deposition
testimony, witness statements, on-site videos, photographs, expert reports, owner's
manuals and every other available scrap of information. He consulted the generally-accepted
toxicological methodology and reference sources. Needless to say, this encompassed
a broad scope of material.
Based on his preliminary findings, Dr. Sawyer prepared a physiologically-oriented
assessment of each victim. The primary focus of his assessment was whether alcohol
intoxication on the part of the victims contributed to their death and whether the
carbon monoxide alarm (had it been operational) would have aroused the victims from
sleep if they were, in fact, intoxicated.
Although Dr. Sawyer relied on the measured postmortem blood levels of COHb (carboxyhemoglobin),
several critical questions remained unanswered. Merely summarizing existing records
was not sufficient to make a determination. Dr. Sawyer found it was necessary to
go further to obtain credible objective evidence involving the circumstances of
death. To that end, a comprehensive accident reconstruction was organized with both
parties (plaintiffs and defendants) present.
By using the same trailer and generator and duplicating the original conditions
as closely as possible, the reconstruction addressed every possible aspect of the
original event. This provided Dr. Sawyer with the opportunity to obtain insights
into unanswered questions arising from the tragedy including:
- Was alcohol a contributing factor in placing the generator in such a hazardous
- How long would it have taken the generator exhaust to raise CO levels within the
trailer enough to trigger the detector?
- How long would it have taken to reach fatal carboxyhemoglobin (COHb) blood levels
in the sleeping victims?
- Did the CO level increase so rapidly that it decreased the victims' ability to
- Or, did the the victims' high blood alcohol levels preclude their awakening even
if the CO detector had been working?
Exposure analysis of the results provided answers to most of the unanswered questions.
Some of the revelations were significant.
Inadvertent Enhancement of Toxicity
An important revelation arising from the accident reconstruction was how the carbon
monoxide became so concentrated. Exhaust fumes entered primarily through a small
storage hatch adjacent to the generator which was not properly closed. The generator
exhaust was pointed directly at the panel. This actually pressurized the contamination,
forcing it inside through seams and small openings.
Although the generator provided overall AC power to the vehicle, the victims mainly
relied on the generator to operate a roof-mounted air conditioner to escape the
August heat. The reconstruction demonstrated several different air intakes and leakage
points throughout the trailer interior. Contaminated air inside the trailer living
area was recirculated back into the living area after being cooled. While such closed-air
containment is a common feature in many air conditioning systems, it had a disastrous
effect in this instance.
A defendant's expert inspecting the system noted that the air conditioner took in
carbon monoxide from the infiltrating generator exhaust. It quickly moved the cooled,
contaminated air to a ceiling vent at the far end of the trailer. Thus, the air
conditioning system concentrated and recirculated the carbon monoxide throughout
the interior, enhancing and accelerating the toxic effects.
Additionally, the generator was placed between an adjacent parked truck and the
trailer (with its "slide-out" extended). This arrangement created a "stagnant air
zone" in which the generator recycled some of its own exhaust gases. This recycling
further increased CO concentrations in the exhaust.
Toxicology of Carbon Monoxide
In assessing the circumstances surrounding the fatalities, Dr. Sawyer relied strictly
on the case facts. Expert testimony must always have its basis in reliable scientific
techniques that are generally accepted by the relevant scientific community. Thus,
although personal observations and professional experience may play a role in formulating
an opinion, they do not constitute an admissible basis for a conclusion. Only by
pragmatically assessing the list of contributing factors and weighing them appropriately
can the expert communicate findings in a scientifically-sound and objective manner.
In the case of carbon monoxide, Dr. Sawyer's report identified the known physiological
characteristics of CO poisoning based on generally-accepted dose-response levels
as shown below:
Dr. Sawyer determined the blood alcohol concentration (BAC) of each victim at the
time the CO detector would have triggered (had it been operative). Then he determined
whether or not alcohol consumption on the part of the victims would have played
a role in decreased vigilance and increased waking time had the detector triggered.
By comparing the carbon monoxide measurements in the accident reconstruction simulation
to the levels measured postmortem (as a function of exposure duration), Dr. Sawyer
was able to back-extrapolate the BAC levels. By comparing these to the generally-accepted,
peer-reviewed exposure characteristics in the toxicological literature, it became
possible to calculate the time required for the victims to reach fatal carboxyhemoglobin
(COHb) blood levels.
Results of Investigation
With only one exception, all of the victims had intoxicating levels of alcohol in
their blood at the time the detector would have sounded (if operational). Multiple
toxicological studies have assessed the impact of blood alcohol levels on the ability
of individuals to awaken and respond to a CO alarm emitting the standard 3100 Hz
Dr. Sawyer worked with an expert audiologist with specialized equipment to monitor
the sound levels throughout the RV at the time the generator was running. Using
specific decibel measurements, the audiologist found that the overbearing engine
noise of the generator would have substantially diminished the decibel
level of the CO detector's alarm. Dr. Sawyer further noted that, in the peer-reviewed
studies, even low blood alcohol levels significantly diminished the ability to
discriminate this particular frequency. Thus, even if the CO detector had been
operational, the victims' level of vigilance and ability to waken from sleep would
have been substantially or completely impaired.
The sole exception was a victim without intoxicating levels of alcohol who might
have reacted to the sound of the alarm (had it been operating). However, the decibel
level of the CO detector was nearly the same as that of the interior generator noise
and adjacent air conditioner located immediately above the victim. This combined
noise would have masked the alarm tone and effectively prevented the victim from
Presentation of Findings
Dr. Sawyer presented his findings in a written report and testimony in deposition.
He noted that the autopsy reports revealed postmortem COHb concentrations as high
as 68%. This represents a "100% lethal" carbon monoxide level. The accident reconstruction
validated this concentration as it revealed a rapid CO rise to 300 ppm (at which
point the detector alarm sounded in the accident reconstruction) and well beyond
that level thereafter.
Dr. Sawyer further noted that the accident reconstruction was scientifically credible
as it was conducted using the original vehicle and all of the equipment present
at the original accident scene. The generator itself was tested and found to be
in proper working order, producing exhaust gases consistent with other units of
Attempts by plaintiffs' counsel to discredit Dr. Sawyer's report and testimony were
unsuccessful. Plaintiffs and defendants settled the case in a manner that satisfied
both parties. It remains uncertain to this day who moved the generator next to the
Word to the Wise
Known as the "silent killer," carbon monoxide is an odorless, tasteless, and colorless
gas. A police officer investigating the event testified that vehicles parked closely
to one another also had generators positioned too closely to the trailers. Those
inside were most fortunate that no other CO poisoning events occurred. Situational
awareness is the key to safety and survival.
(Disclaimer: Toxicology case studies are impartial and objective summaries of toxicological
matters in which TCAS was retained for the purpose of assessing health-based
factors which, in some cases, led to a determination of causation. In the above
matter, Dr. Sawyer was retained by defendants)
- Public domain image courtesy of WikiMedia Commons (redacted)
- Accident reconstruction photo (redacted)
- Image adapted from U.S. CDC, ATSDR, 2012
- Image copyright TCAS, LLC, All Right Reserved
- Image copyright TCAS, LLC, All Right Reserved