Carbon Monoxide Poisoning Claims: Landlord Liability

Carbon monoxide poisoning is unusual among injury claims in that the evidence proving it starts disappearing immediately — from the air, from the blood, and from the building, where the faulty appliance will be repaired or replaced within days. Meanwhile the injury that matters most often has not appeared yet.

Quick answer: The COHb blood level proving exposure declines over time and faster on oxygen, so a level drawn late understates the real exposure. Symptoms are routinely misdiagnosed as flu, and the giveaway is several people in one building ill at once. Liability usually rests on a missing or defective alarm — required by most states and many local codes — or on unmaintained fuel-burning equipment or ignored tenant complaints. The lasting harm is frequently delayed neurological injury appearing days to weeks later.

Why These Cases Are Missed

The gas gives no warning: no colour, no smell, no taste. The early presentation — headache, nausea, dizziness, fatigue, confusion, shortness of breath — is indistinguishable from a viral illness, and an emergency department that is not prompted to consider carbon monoxide will frequently not measure for it.

The patterns that should raise it:

• Multiple people in the same building ill simultaneously, including pets
• Symptoms that improve on leaving the property and return on coming back
• Onset coinciding with the heating season or with the first use of an appliance after a period of disuse
• A generator running in or near an enclosed space, particularly after a storm or power outage
• A vehicle left running in an attached garage

This diagnostic difficulty is not incidental to the legal claim — it produces the two problems the rest of this guide is about: the exposure evidence fades, and the causal link between a later cognitive problem and an earlier “flu” gets contested.

The COHb Timing Problem

A carboxyhaemoglobin (COHb) level is the direct measure of exposure. Its evidentiary weakness is that it falls with time, and falls considerably faster once supplemental oxygen is administered — which is, correctly, the first treatment given.

The consequence is a defence argument that appears in almost every one of these cases: the level was only mildly elevated, so the exposure was mild. That inference does not hold if the sample was drawn hours after removal from the source or after oxygen therapy had begun. Establishing the timeline — when the person left the environment, when treatment started, when blood was drawn — is what makes a modest recorded level consistent with a serious exposure.

This is also why the on-scene readings matter so much independently. Fire departments and gas utilities measure ambient concentration in parts per million when they respond, and that measurement documents the hazard itself rather than one person’s absorbed dose.

Where the Gas Comes From, and Who Is Responsible

Common sources, each pointing at different defendants:

• Furnaces and boilers — cracked heat exchangers, blocked or disconnected flues
• Water heaters — improper venting, backdrafting
• Gas ranges and space heaters — used for heating, or unvented
• Blocked or deteriorated chimneys and vents, including bird nests and snow obstruction
• Portable generators, the classic post-storm mechanism, run in a garage, basement or too close to a window
• Vehicles idling in attached garages
• Pool and spa heaters, and hotel boiler rooms adjacent to guest rooms

The landlord or property owner owes the premises duty described in our guide to slip and fall claims at an apartment or rental property, and here it typically resolves into three concrete questions: was a required alarm present and working, was the fuel-burning equipment maintained and inspected, and were tenant complaints acted on.

An HVAC, plumbing or chimney contractor that installed, serviced or certified the equipment negligently — often the party whose records show the failure most clearly.

The manufacturer of a defective appliance or generator, on design or failure-to-warn theories described in our guide to defective product claims.

A hotel or short-term rental operator, which faces both the premises duty and, in many jurisdictions, specific alarm requirements.

A property manager distinct from the owner, and in some circumstances a utility company.

The Alarm Requirement Is the Cleanest Liability Route

Most states, and many local building and fire codes, now require carbon monoxide alarms in dwellings, with rental units and sleeping areas most commonly covered. Requirements typically come from a combination of state statute, adopted building and fire codes, and referenced standards published by the NFPA.

That matters for the same reason a building code violation matters in any premises case: it converts “should have been more careful” into a specific, checkable requirement that was or was not met. The provable failures tend to be:

• No alarm installed where one was required
• An alarm removed, disabled or with a dead battery
• An alarm past its service life, since CO sensors expire
• An alarm installed in the wrong location or not in the required sleeping areas

Because requirements vary by state and municipality, the specific rule for your property should be confirmed locally rather than assumed.

Notice: What the Landlord Already Knew

As in any premises claim, notice frequently decides the outcome — the framework set out in our guide to slip and fall settlements against a business. What establishes it here:

• Prior tenant complaints — headaches, a smell of gas, a pilot light that keeps going out, a heater that “smells funny”
• Prior service calls on the same equipment, particularly repeat visits for the same fault
• A deferred repair — a recommendation the owner declined to act on
• Inspection or code enforcement history on the property
• Prior incidents at the same building
• The age and service record of the equipment

A documented recommendation to replace a cracked heat exchanger that was not acted on is, in this context, the equivalent of the sweep log gap in a slip and fall case.

Delayed Neurological Injury: Where the Value Usually Is

The acute poisoning is often not the main injury. A well-recognised pattern involves apparent recovery followed, days to weeks later, by delayed neurological and neuropsychiatric effects: memory impairment, reduced concentration, executive dysfunction, personality and mood change, headache, and in some cases movement disorders.

Two implications:

1. Medically, anyone with a significant exposure should be followed rather than discharged and forgotten, and neuropsychological testing is the tool that objectively characterises cognitive deficits — the same evidence that carries a traumatic brain injury claim, and it is treated similarly in valuation.
2. Legally, this is where causation is fought. The defence will attribute later cognitive complaints to stress, depression, unrelated causes, or the original “flu.” Contemporaneous documentation connecting the later findings back to the exposure is what answers that.

Serious acute cases can also produce cardiac injury and, in pregnancy, harm to the foetus.

Multiple Victims, One Policy

Carbon monoxide rarely affects one person. A household, a floor of an apartment building, or a group of hotel guests may all be exposed at once, and each has their own claim.

That creates the limited-fund problem our guide to multiple claimants and one policy addresses: where several serious claims draw on a single liability policy, the available coverage rather than the injuries may set the ceiling, and timing matters more than it would in an ordinary claim. Identifying all available coverage — the owner’s policy, a contractor’s policy, a manufacturer’s, and any umbrella layer — is correspondingly more important.

Practical Steps

1. Get out and call emergency services from outside. Do not investigate the appliance yourself.
2. Ask responders to record their readings, and get the incident number for the fire department and utility response.
3. Tell the treating clinician carbon monoxide is suspected, so a COHb level is drawn — and record the time it was drawn and when oxygen was started.
4. Do not let the appliance be repaired, replaced or discarded. Send a preservation demand naming the equipment, the detector and the service records within days.
5. Photograph everything — the appliance, the venting, the detector or the empty bracket where one should have been, and the room layout.
6. Collect every prior complaint you or other tenants made, in whatever form it exists: texts, emails, portal tickets, letters.
7. Get everyone exposed evaluated, including children and anyone who felt fine.
8. Arrange follow-up rather than assuming recovery, and raise neuropsychological testing if cognitive symptoms appear in the following weeks.

Sources & Further Reading

• Restatement (Second) of Torts §§ 343, 343A — a possessor’s duty to entrants regarding conditions on the premises
• State carbon monoxide alarm statutes and local building and fire code requirements for dwellings, rental units and hotels, which vary by jurisdiction and should be confirmed locally
• NFPA standards on carbon monoxide detection and warning equipment, referenced by many adopting codes
• CDC and CPSC carbon monoxide poisoning surveillance and prevention materials, including generator-related fatality data
• Clinical literature on carboxyhaemoglobin half-life and its reduction with supplemental oxygen, and on delayed neurological sequelae following acute poisoning
• See our guides to slip and fall claims at an apartment or rental property for the landlord duty framework, slip and fall settlements against a business for how notice is established, defective product claims for the appliance or generator theory, and traumatic brain injury settlement value for how cognitive deficits are documented and valued
• See our guides to slip and fall claims at an apartment or rental property for the landlord duty framework, slip and fall settlements against a business for how notice is established, defective product claims for the appliance or generator theory, and traumatic brain injury settlement value for how cognitive deficits are documented and valued
• Where the property is a hotel or motel, a heightened common-law duty applies on top of the ordinary premises framework — see our guide to hotel and motel guest injury claims