Carbon monoxide is dangerous because it gives little warning before it begins impairing the person breathing it. It is a colorless, odorless gas produced when carbon-based fuels burn incompletely, and the CDC describes it as capable of causing sudden illness and death without warning.1 In commercial trucking, that danger is different from the household cases most people associate with furnaces or generators. A truck cab is both a workplace and, for long-haul drivers, a sleeping space. A driver may spend hours inside a closed cab with the engine idling, a bunk heater running, an auxiliary power unit operating nearby, or another truck idling close enough for exhaust to enter through vents or cab openings.
The national numbers show why carbon monoxide cannot be treated as a rare hazard. CDC estimates that unintentional, non-fire carbon monoxide exposure kills more than 400 Americans each year, sends more than 100,000 people to emergency departments, and causes more than 14,000 hospitalizations annually.1 Occupational data show the same pattern in work settings. A NIOSH-authored study of occupational carbon monoxide fatalities from 1992 through 2008 found an average of 22 occupational carbon monoxide deaths per year, and identified motor vehicles as the most frequent source of fatal occupational carbon monoxide exposure.2
For truck drivers, the risk is not limited to one source.
Carbon monoxide can enter the cab from:
- Exhaust leaks
- Cracked or separated exhaust components
- Holes in the floorboard
- Firewall openings
- Failed sleeper-berth seals
- Nearby idling vehicles
- Malfunctioning bunk heaters
- Auxiliary power units
- Portable heaters
- Fuel-burning cooking devices
The central problem is that the early symptoms—headache, dizziness, nausea, weakness, fatigue, drowsiness, confusion—can look like ordinary tiredness or illness until the driver is too impaired to react. OSHA identifies headache, fatigue, dizziness, drowsiness, and nausea as symptoms of carbon monoxide poisoning, with prolonged or high exposure leading to vomiting, confusion, collapse, loss of consciousness, muscle weakness, and death.3
How Carbon Monoxide Gets into a Truck Cab
Federal motor carrier rules recognize that exhaust location and cab integrity matter. Section 393.83 requires vehicles with combustion engines to have exhaust systems that direct harmful combustion fumes away from the vehicle and its occupants. For trucks and truck tractors, the exhaust must discharge either to the rear of the cab or, if the exhaust projects above the cab, near the rear of the cab. The same rule prohibits temporary patch or wrap repairs, requires the exhaust system to be securely fastened, and prohibits exhaust leaks or discharges forward of or directly below the driver or sleeper compartment.4
The floor of the cab is part of the same safety system. Section 393.84 requires vehicle floors to be “substantially constructed, free of unnecessary holes and openings, and…maintained so as to minimize the entrance of fumes, exhaust gases, or fire.”
A federal technical report on toxic gases in heavy-duty diesel truck cabs found that cab floor openings were a principal pathway for transmission of gases from the engine compartment into the cab.6 The same report linked elevated in-cab gas concentrations with factors including window condition, cab configuration, exhaust leaks, and underside cab openings. Those findings explain why carbon monoxide investigations should include the cab structure, not just the tailpipe.
Truck manufacturers warn about the same problem. Peterbilt’s Model 579 operator’s manual states that engine exhaust contains carbon monoxide and that “a poorly maintained, damaged, or corroded exhaust system can allow carbon monoxide to enter the cab.” The manual also warns that carbon monoxide can enter the cab from nearby vehicles and instructs drivers never to idle the vehicle for prolonged periods if exhaust fumes are entering the cab.7
Why Carbon Monoxide Looks Like Fatigue
Carbon monoxide poisoning is easy to miss because its early symptoms are nonspecific. CDC clinical guidance lists headache, dizziness, weakness, nausea, vomiting, chest pain, and altered mental status as common symptoms. Severe poisoning can involve neurologic symptoms, ataxia, loss of consciousness, coma, and death.8
That medical progression is especially dangerous in trucking because the first symptom may be interpreted as ordinary fatigue. FMCSA’s CDL manual warns drivers that exhaust-system leaks are especially dangerous when cab ventilation is poor, that loose exhaust connections can permit poisonous carbon monoxide to enter the vehicle, and that carbon monoxide can make a driver sleepy and can kill in large enough amounts.9 In other words, the symptom that may tell a driver something is wrong, sleepiness, is also the condition that can keep the driver from responding in time.
NIOSH explains that carbon monoxide can accumulate rapidly in enclosed or semi-enclosed areas, sometimes even where ventilation appears adequate, and that exposed workers may have little time before symptoms inhibit their ability to seek safety. NIOSH also lists headache, confusion, fatigue, seizures, dizziness, loss of consciousness, and nausea as potential symptoms.10
Real incident summaries show how easily carbon monoxide can be confused with another medical condition. OSHA’s accident database describes a truck driver who lost consciousness in a parked truck, was initially treated for a stroke, and was later determined by toxicology to have died from carbon monoxide poisoning.11 That kind of case illustrates why carbon monoxide should remain on the investigative checklist when a driver becomes confused, incapacitated, or unconscious without a clear traumatic explanation.
Diesel Exhaust Is Not Carbon-Monoxide-Free
A common misconception is that diesel engines do not create meaningful carbon monoxide risk because they generally produce lower carbon monoxide concentrations than gasoline engines. The second half of that statement does not follow from the first. OSHA has stated that carbon monoxide is one component of diesel engine emissions, and identifies acute carbon monoxide symptoms as headache, dizziness, drowsiness, nausea, vomiting, collapse, coma, and death.12
OSHA’s diesel exhaust hazard materials also identify truck drivers and truck or bus maintenance garage workers as occupations that may be exposed to diesel exhaust.13 Those materials explain that short-term exposure to high concentrations of diesel exhaust or diesel particulate matter can cause headache, dizziness, and irritation of the eye, nose and throat severe enough to distract or disable miners and other workers. OSHA lists carbon monoxide among regulated components of diesel exhaust and identifies the OSHA permissible exposure limit for carbon monoxide as 50 parts per million as an eight-hour time-weighted average.13
The diesel-specific fatality literature supports the same point. A forensic case report titled “Diesel fumes do kill” explains that diesel engines “produce much lower carbon monoxide concentrations than gasoline engines”, but that diesel exhaust can still “generate lethal ambient carbon monoxide concentrations given enough time in an enclosed space and suitable environmental conditions.”14 The case involved a truck driver found dead in the cab of a running diesel tractor-trailer, with toxicology establishing lethal carbon monoxide exposure.
That does not mean every diesel truck cab is a carbon monoxide hazard. It means diesel exhaust should not be dismissed during investigation. The relevant questions are whether combustion gases were produced, whether they were routed away from the cab, whether exhaust leaks or cab openings existed, whether the vehicle was idling, whether ventilation conditions allowed accumulation, and whether the driver’s symptoms fit carbon monoxide exposure.
Federal Rules Treat Carbon Monoxide as an Out-of-Service Hazard
The Federal Motor Carrier Safety Regulations do not treat carbon monoxide as a minor maintenance issue. Section 392.66 provides that a person may not dispatch, drive, or permit passengers on a commercial motor vehicle when an occupant has been affected by carbon monoxide, when carbon monoxide has been detected inside the vehicle, or when a mechanical condition likely to create a carbon monoxide hazard has been discovered, until the condition has been remedied or repaired.15
That rule is important because carbon monoxide exposure often produces indirect evidence before it produces a crash. A driver may report exhaust smell, headache, nausea, dizziness, unusual drowsiness, burning eyes, sleeper fumes, or a cab that “make him sick.” A mechanic may find a loose clamp, rusted flex pipe, missing exhaust hanger, cracked manifold, failed gasket, leaking bunk-heater exhaust, or damaged underbody seal. Once carbon monoxide is detected or a likely carbon monoxide-producing mechanical condition is discovered, continued operation is not supposed to be a paperwork issue; the vehicle must be repaired before use.
The maintenance rules reinforce that point. Section 396.3 requires motor carriers to systematically inspect, repair, and maintain vehicles under their control, and to keep parts and accessories in safe and proper operating condition.16 The same rule requires maintenance records that identify the vehicle, show the nature and due date of inspection and maintenance operations, and record the date and nature of inspection, repair, and maintenance work performed.16
Driver vehicle inspection reports can also become central evidence. Section 396.11 requires drivers to report defects or deficiencies discovered by or reported to the driver when those conditions would affect safe operation or result in mechanical breakdown.17 Before the carrier allows the vehicle to operate again, the carrier must repair listed defects likely to affect safe operation or certify that repair is unnecessary.17
Sleeper Berths, Heaters, and Secondary Sources
Not every carbon monoxide exposure in trucking begins with the truck’s main exhaust pipe.
Sleeper cabs may contain or be exposed to other combustion sources, including:
- Bunk heaters
- Auxiliary power units
- Portable stoves
- Propane or butane devices
- Nearby idling trucks
- Generators
- Equipment operating near docks or terminals
CPSC’s 2021 annual estimates report found 204 estimated unintentional, non-fire carbon monoxide deaths associated with consumer products in 2021, with engine-driven tools and heating systems among the major source categories.18
A Washington FACE investigation shows why those secondary sources matter in trucking. The report described a 61-year-old general-freight truck driver who died from carbon monoxide poisoning after resting in a sleeper berth at his employer’s terminal yard. Investigators concluded that the most likely source was a single-burner butane cooking stove inside the cab, rather than the truck’s engine exhaust system.19
The FACE report recommended:
- Vehicle-rated carbon monoxide detector alarms in truck cabs and sleeper berths
- Policies prohibiting butane, propane, and other fuel-burning cooking stoves or space heaters inside cabs and sleepers
- Preventive maintenance checks on engine and bunk-heater exhaust systems
- Avoiding parking near idling trucks or auxiliary power units because fumes can enter even when windows and vents are closed.19
NIOSH likewise recommends regular engine and exhaust-system maintenance inspections and carbon monoxide detectors or personal monitors where carbon monoxide sources may exist.10
The sleeper-berth issue changes the investigation. A driver may be exposed while asleep, when symptoms cannot be recognized. CDC warns that people who are sleeping or intoxicated can die from carbon monoxide poisoning before experiencing symptoms.1 A sleeper-cab carbon monoxide investigation should therefore examine not only exhaust routing, but also bunk-heater exhaust, auxiliary power units, idling neighbors, cab ventilation, portable fuel-burning equipment, detector history, and where the truck was parked.
What Discovery and Investigation Usually Focus On
Carbon monoxide cases are often built from ordinary maintenance and medical records rather than a single dramatic piece of physical evidence.
Relevant records include:
- Driver vehicle inspection reports, repair orders, and exhaust complaints
- “Fumes in cab” complaints, headache or dizziness reports, and service invoices
- Emissions or exhaust repairs, bunk-heater maintenance, and auxiliary power unit service
- Photographs of cab openings, floorboard condition, and firewall penetrations
- HVAC intake location
- Carbon monoxide detector data
An employment law case from Oregon shows how these issues appear in litigation. In Herbert v. Altimeter, Inc., a truck driver alleged carbon monoxide exposure while operating a long-haul tractor, and the court discussed evidence of repeated exhaust-related maintenance, including flex-pipe and band-clamp work, head-gasket work, and a prior maintenance log noting a “big exhaust leak.”20 The court also discussed expert testimony from a diesel mechanic that exhaust leaks around flex pipes and band clamps are common in trucking, can be hard to find and remedy, and can create carbon monoxide poisoning risk.20
Other vehicle carbon monoxide cases show recurring proof issues. In Clary v. Fifth Avenue Chrysler Center, the Alaska Supreme Court discussed evidence that missing body drain plugs and a loose exhaust clamp could have allowed carbon monoxide to enter the passenger compartment.21 In Garrido v. Team Auto Sales, the South Dakota Supreme Court held that delayed low-level carbon monoxide testing did not defeat the claim where symptoms, vehicle condition, and expert testimony supported exposure, including testimony that carbon monoxide can dissipate rapidly after doors are opened and the vehicle is ventilated.22
Modern vehicle carbon monoxide litigation also focuses on pathway testing. In Bellamy v. Ford Motor Co., a Texas federal court discussed expert opinions that exhaust leaks provided a source of carbon monoxide and that fumes could enter the passenger compartment through the fresh-air vent after the vehicle had been driven and then parked at idle.23 In Cashatt v. Ford Motor Co., the court described claims involving alleged exhaust and HVAC defects, cracked manifolds, warped Y-pipes, fresh-air intake pathways, and symptoms such as headaches, vomiting, nausea, foggy thinking, and flu-like illness.24
These cases point to a basic investigative rule: carbon monoxide dissipates, repairs change the evidence, and a later “normal” reading may not reconstruct the earlier exposure. Medical evidence has its own timing issues. CDC clinical guidance explains that carboxyhemoglobin levels support diagnosis, but the usefulness of the test depends on how much time has passed since the person left the toxic environment and whether treatment has begun.8 That is why investigators compare symptoms, blood-draw timing, oxygen treatment, exposure duration, source testing, vehicle condition, repair history, and alternative sources.
Why the Failure Is Systemic
An exhaust leak is rarely just a broken pipe. In a commercial truck, it can reflect a maintenance system that missed corrosion, ignored driver symptoms, deferred exhaust repairs, failed to inspect cab openings, or treated carbon monoxide symptoms as ordinary fatigue. Federal rules require exhaust systems to route fumes away from the cab, floors to minimize fume intrusion, vehicles to be maintained systematically, and carbon monoxide hazards to be repaired before operation.
The evidence usually sits in plain records:
- Prior exhaust complaints
- Loose clamps, patched pipes, missing plugs
- Sleeper-heater work
- Idling policies
- Detector history
- Driver reports of headache or sleepiness
The danger is that carbon monoxide does not wait for a driver to understand the cause. It impairs judgment first, then coordination, consciousness, and control. In a moving tractor-trailer, that progression can turn a hidden maintenance defect into a roadway emergency before anyone outside the cab knows something is wrong.
Sources
- [1] Centers for Disease Control and Prevention, "Carbon Monoxide Poisoning Basics," January 12, 2026,.
- [2] Henn SA, Bell JL, Sussell A, Konda S, "Occupational Carbon Monoxide Fatalities in the US from Unintentional Non-Fire Related Exposures, 1992–2008," American Journal of Industrial Medicine, 2013,.
- [3] Occupational Safety and Health Administration, "Carbon Monoxide Poisoning" (Fact Sheet DSG FS-3522), April 2012,.
- [4] Code of Federal Regulations, "Title 49, Section 393.83 (Exhaust Systems),".
- [5] Code of Federal Regulations, "Title 49, Section 393.84 (Floors),".
- [6] Ziskind R, Carlin T, Axelrod M, Allen RW, Schwartz SH, "Toxic Gases in Heavy Duty Diesel Truck Cabs," Federal Highway Administration/Bureau of Motor Carrier Safety, Technical Report No. PB275957, 1977,.
- [7] Peterbilt, "Model 579 Operator's Manual," 2021,.
- [8] Centers for Disease Control and Prevention, "Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe Weather,".
- [9] Federal Motor Carrier Safety Administration, "Commercial Driver's License Manual," 2005 (July 2010 update),.
- [10] National Institute for Occupational Safety and Health, "Carbon Monoxide Hazards at Work," September 30, 2024,.
- [11] Occupational Safety and Health Administration, "Accident Report Detail, Nr: 157475.015—Employee Dies Due to Carbon Monoxide Poisoning,".
- [12] Occupational Safety and Health Administration, "Standard Interpretation: Diesel Engine Emissions and Carbon Monoxide" (Letter to Alfred C. Rapin), November 8, 1985,.
- [13] Occupational Safety and Health Administration and Mine Safety and Health Administration, "Diesel Exhaust/Diesel Particulate Matter" (OSHA-HA-3590-2013),.
- [14] Griffin SM, Ward MK, Terrell AR, Stewart D, "Diesel Fumes Do Kill: A Case of Fatal Carbon Monoxide Poisoning Directly Attributed to Diesel Fuel Exhaust with a 10-Year Retrospective Case and Literature Review," Journal of Forensic Sciences, 2008,.
- [15] Code of Federal Regulations, "Title 49, Section 392.66 (Carbon Monoxide; Use of Commercial Motor Vehicle When Detected),".
- [16] Code of Federal Regulations, "Title 49, Section 396.3 (Inspection, Repair, and Maintenance),".
- [17] Code of Federal Regulations, "Title 49, Section 396.11 (Driver Vehicle Inspection Reports),".
- [18] U.S. Consumer Product Safety Commission, "Non-Fire Carbon Monoxide Deaths Associated with the Use of Consumer Products, 2021 Annual Estimates," February 2025,. (figures exclude CO deaths solely from motor vehicles and directly work-related exposures)
- [19] Washington State Department of Labor & Industries, "Truck Driver Poisoned by Carbon Monoxide in Cab" (FACE Investigation Report No. 71-254-2024), 2024,.
- [20] Herbert v. Altimeter, Inc., Case A136664 (Or. Ct. App. Sept. 9, 2009).
- [21] Clary v. Fifth Avenue Chrysler Center, Inc., 454 P.2d 244 (Alaska 1969).
- [22] Garrido v. Team Auto Sales, Inc., 2018 SD 41, 913 N.W.2d 95.
- [23] Bellamy v. Ford Motor Co., No. SA-22-CV-00941-JKP (W.D. Tex. Jan. 6, 2025).
- [24] Cashatt v. Ford Motor Co., No. 3:19-cv-05886-TMC (W.D. Wash.).