Short definition
The carbon monoxide (CO) hazard is the risk of poisoning from carbon monoxide gas — a colorless, odorless, tasteless byproduct of incomplete combustion. CO binds tightly to hemoglobin and blocks oxygen transport, causing headache, confusion, unconsciousness, and death at concentrations a person cannot detect without a sensor.
What it is
CO forms whenever a carbon fuel — natural gas, propane, oil, wood, gasoline — burns without enough oxygen for complete combustion. A properly tuned blue-flame burner produces almost no CO; the same burner with a blocked flue, dirty heat exchanger, or starved combustion air can produce dangerous levels.
The medical mechanism: CO binds to hemoglobin roughly 200 to 300 times more strongly than oxygen does. Even small amounts in the air displace oxygen on red blood cells. Symptoms progress through headache, dizziness, nausea, a “spinning” feeling, confusion, loss of consciousness, and death. Concentrations near 1% in room air are rapidly fatal.
The danger is that humans cannot smell, see, or taste it. By the time symptoms register, judgment may already be impaired enough that the person doesn’t act. That is the entire reason for the CO alarm — it senses what people cannot.
Why it matters to a homeowner
CO is the leading cause of accidental poisoning death in the United States — roughly 400 deaths and 50,000 ER visits a year per CDC tracking. The Pacific Northwest has a recurring winter pattern: power outages from a windstorm, generators or unvented heaters used indoors or in attached garages, multiple people poisoned at once. The December 2006 windstorm killed eight people in Washington from CO alone. The January 2024 cold snap added more.
The everyday-residential sources matter just as much as the storm scenario. A back-drafting water heater in a tightened-up utility room, a cracked furnace heat exchanger, a blocked B-vent, an idling vehicle in an attached garage — any of these can produce hospital-trip levels of CO over hours, in a household that has no idea what’s happening.
When you’ll encounter this term
- A whole household reports recurring headaches or “winter flu” that goes away when leaving the house
- A power outage and the question of where to run a generator
- An older home tightened up with new insulation, and the water heater starts to back-draft
- Annual furnace inspection: tech mentions combustion analysis or low draft
- A car warming up in an attached garage with the door closed
Common variants and what CO is not
- CO vs. CO2. CO is toxic at low ppm; CO2 is what we exhale and only becomes dangerous as an asphyxiant at very high concentrations. CO alarms do not detect CO2.
- CO vs. natural gas. Methane is non-toxic but explosive; the rotten-egg smell is mercaptan added for detection. CO alarms do not detect raw natural gas leaks — that’s a different hazard.
- Acute vs. chronic exposure. Acute high-level exposure is the headline (≥150 ppm short term). Chronic low-level (10–30 ppm continuous from a marginal appliance) often presents as recurring headaches and fatigue, easy to misdiagnose for months.
Common failure modes (sources of CO in WA homes)
- Back-drafting atmospheric gas water heater — negative pressure in a tight utility room pulls flue gas back into living space.
- Cracked heat exchanger in an older furnace — bleeds CO into the supply air.
- Blocked B-vent or chimney — bird nest, ice plug, debris.
- Idling vehicle in an attached garage — among the most common fatal CO events in the PNW.
- Generator placed too close to the house during a storm — CO migrates through windows, vents, doors. Run generators outdoors, far from any opening, even with the garage door open.
- Unvented “blue flame” propane heaters used indoors during power outages — never safe in a closed living space.
Washington note
Washington requires CO alarms in essentially all residential buildings under RCW 19.27.530. The law exists because of this hazard.
The PNW pattern that drives the local relevance: cold-weather windstorms knock out power for hours to days; households improvise with generators, vehicles, or unvented heaters; CO accumulates in living space; people sleep through it. Washington Department of Health PSAs and county emergency management agencies publish the same rules every winter — generators must run outdoors at least 20 feet from any door, window, or vent; never use a charcoal grill, camp stove, or unvented heater indoors; never warm up a vehicle in an attached garage.
If your alarm sounds, leave the house immediately, account for everyone, and call 911 from outside. Do not go back in to investigate.
FAQ
What are the symptoms of carbon monoxide poisoning?
Early: headache, dizziness, nausea, a “spinning” or unsteady feeling. Middle: confusion, blurred vision, weakness, vomiting. Late: chest pain, loss of consciousness, seizures, death. The hallmark sign is that everyone in the household (and pets) feels it at the same time, and symptoms ease when you leave the house and return when you come back. Treat that pattern as CO until proven otherwise.
Can carbon monoxide come from a fireplace or wood stove?
Yes. Any combustion appliance can produce CO if the chimney is blocked, the damper is closed, or combustion air is inadequate. Wood-burning fireplaces produce more CO than properly tuned gas appliances do, especially with damp wood or a smoldering fire. A working CO alarm on the floor with the fireplace is the right safeguard.
Is it safe to run a generator in the garage if the door is open?
No. Generators must run outdoors, ideally 20 feet or more from any door, window, or vent. Open garage doors do not provide enough ventilation, especially in cold or wind. CO from a generator inside an attached garage migrates into the living space within minutes. This is the single most common fatal CO scenario during PNW windstorms.