Carbon monoxide

Carbon monoxide is produced whenever carbon-containing fuels burn incompletely [1]. The gas engine, the gas furnace, the gas stove, the wood fireplace, the kerosene heater, the portable generator, and the charcoal grill all produce CO. It was recognized as a poison in the early 19th century and became a major public health issue as gas lighting and then gas heating became standard in urban homes — deaths from gas leaks and faulty heating equipment were a recurring tragedy throughout the industrial era [2]. The largest modern source of CO emissions is vehicle exhaust, which is why running a car in an attached garage or enclosed space is rapidly fatal. Generators represent a newer acute risk: during power outages, people bring portable generators indoors or into garages, where CO rapidly accumulates. The CDC estimates that generators cause more than 400 CO poisoning deaths annually during and after natural disasters [3]. Wildfire smoke contains CO at concentrations that can be hazardous during extended smoke events.

Heating equipment — furnaces, boilers, and water heaters with blocked flues, cracked heat exchangers, or insufficient combustion air — is the leading cause of residential CO poisoning deaths [1]. Gas stoves and ovens contribute meaningful CO to kitchen air, particularly during extended cooking or when used for supplemental heat (extremely dangerous). Attached garages are a critical pathway: exhaust from a running vehicle in an attached garage infiltrates the living space within minutes, even with the garage door open [2]. Portable generators, charcoal grills, and propane or kerosene heaters used indoors during camping or power outages are responsible for many acute deaths. Tobacco smoke is a significant source of chronic low-level CO exposure for smokers and people in smoke-filled environments [3].

Carbon monoxide binds to hemoglobin with 200 times the affinity of oxygen, forming carboxyhemoglobin (COHb) that cannot carry oxygen [1]. At low COHb levels (10–20%), symptoms mimic the flu: headache, nausea, dizziness, and fatigue — a dangerous mimicry that leads many people to attribute CO poisoning symptoms to other causes and fail to leave the contaminated space. At higher levels (30–40%), confusion, disorientation, and loss of coordination develop. Above 50–60% COHb, unconsciousness and death follow rapidly [2]. Survivors of significant CO poisoning frequently experience delayed neurological effects that emerge days to weeks after apparent recovery: memory problems, personality changes, Parkinsonism, and dementia-like cognitive deficits. The brain and heart are most vulnerable due to their high oxygen demands — CO poisoning survivors have elevated rates of cardiac complications and neurological disability [3].

Everyone in a home with combustion appliances, an attached garage, or exposure to generator or vehicle exhaust faces CO risk [1]. Elderly individuals, people with heart or lung disease, fetuses, and young children are most susceptible to CO's effects at a given exposure level — they have less physiological reserve. People who sleep through early poisoning symptoms (headache, nausea) are at particular risk because CO can reach fatal levels during sleep [2]. People who live in poorly maintained rental housing with older heating equipment that is rarely serviced face chronically elevated CO exposures that may cause subtle chronic effects even without acute poisoning events [3].

Install a UL-listed CO detector on every floor of your home, especially near sleeping areas — this is the single most important protective action [1]. Test detectors monthly and replace batteries annually (or use 10-year sealed-battery units). Never run a generator indoors, in a garage, or within 20 feet of any window or door — even with doors open. Never use a gas oven, charcoal grill, or propane heater indoors for heat [2]. Have your furnace, boiler, and gas appliances inspected annually by a qualified technician; ensure all flues and vents are clear. Never warm up a vehicle in an attached garage, even with the garage door open. During wildfires, keep windows closed and run air purifiers — CO and other combustion gases in wildfire smoke can be significant [3]. If your CO detector sounds, leave immediately, get fresh air, and call 911 before re-entering.