CO is invisible and odourless — know the sources, symptoms, detector placement rules, and emergency steps that save lives before you need them.
Carbon monoxide is called the "silent killer" for good reason. It has no colour, no smell, and no taste. By the time you feel the effects, you may already lack the cognitive clarity to act. Approximately 400 Americans die from unintentional non-fire-related CO poisoning each year, and more than 100,000 people visit emergency rooms. These numbers spike dramatically during winter storms and power outages, when people use gas generators, portable heaters, and stoves indoors in ways they were never designed to be used.
Unlike most home hazards, CO is entirely invisible until it has already started harming you. Your only reliable protection is a functioning detector and the knowledge to act correctly when it sounds.
Carbon monoxide (CO) is a gas produced when carbon-containing fuels are burned without adequate oxygen — a process called incomplete combustion. Any fuel-burning appliance or engine can produce it. CO binds to haemoglobin in your blood roughly 200–250 times more readily than oxygen, preventing your blood from carrying oxygen to your brain, heart, and organs.
At low concentrations, CO causes headaches and nausea. At moderate concentrations it causes loss of consciousness. At high concentrations it causes death within minutes. Because it affects brain function early in the poisoning process, victims often cannot identify what is happening to them — they may feel tired, assume they have the flu, and fall asleep rather than escaping.
| Source | Risk Level | Notes |
|---|---|---|
| Portable petrol generator | Extremely High | Never use indoors or in a garage; kills within minutes at close range |
| Gas/petrol-powered tools | Very High | Pressure washers, lawn mowers — garage and ventilation critical |
| Gas cookers and ovens | Moderate-High | Risk rises sharply if used for space heating |
| Gas boilers | Moderate | Annual servicing reduces risk significantly |
| Gas water heaters | Moderate | Must be properly vented to exterior |
| Fireplaces (wood and gas) | Moderate | Blocked or unswept chimneys are a common cause |
| Charcoal/wood BBQs | High | Never burn charcoal indoors — even partly, even after use |
| Paraffin (kerosene) heaters | Moderate | Need good ventilation; never in sleeping areas |
| Cars in garages | High | Even briefly running a car produces dangerous levels |
| Blocked flues and chimneys | High | Annual inspection essential |
⚠️ Using a generator, BBQ, or gas cooker to heat a home during a power outage is one of the most common ways people die from CO poisoning. The surge in CO deaths during winter storms is almost entirely driven by this behaviour.
Symptoms are notoriously easy to dismiss as flu or tiredness:
Key indicator: Multiple people in the same building developing similar symptoms simultaneously — especially headaches and nausea. Pets may show signs before humans because of their smaller body mass.
Another indicator: Symptoms that improve when you leave the building and return when you come back. CO poisoning is one of the few conditions that gets better with fresh air.
⚠️ Do not assume these symptoms are the flu. If they occur in winter, especially if multiple household members are affected, or if they improve when you go outside, treat this as a potential CO emergency.
A CO detector is the only reliable early warning system for carbon monoxide. Smoke alarms do not detect CO; they are separate devices.
| Location | Guidance |
|---|---|
| Every level of the home | Including basement |
| Outside each sleeping area | So the alarm wakes sleeping occupants |
| Near fuel-burning appliances | But not directly adjacent — at least 1.5 metres away to avoid nuisance alarms from start-up puffs |
| Garages | Only if attached to living space and you run engines inside |
| Height | Most manufacturers recommend 1–1.5 metres high (breathing height) — CO mixes with air rather than rising or sinking like some gases |
Like smoke detectors, CO alarms should ideally be interconnected so that when one detects CO, all units in the home sound. This is critical for large homes and two-storey properties.
| Task | Frequency |
|---|---|
| Test alarm button | Monthly |
| Replace batteries | Annually (or use 10-year sealed units) |
| Replace the entire unit | Every 5–7 years (per manufacturer — sensor elements degrade) |
| Check for damage or dust | Monthly |
| Professional boiler service | Annually |
| Chimney sweep and inspection | Annually before heating season |
Electrochemical CO sensor elements have a finite lifespan regardless of whether the unit has ever alarmed. An expired sensor may not detect CO even when the unit's battery and electronics are functioning. Check the manufacture date on the back of every detector you own.
The response to a CO alarm must be immediate and decisive. Do not assume it is a false alarm.
⚠️ Some CO detectors have different alarm patterns for low-level long-duration exposure (typically 4 beeps, pause, 4 beeps) versus emergency-level exposure. Know your detector's alert patterns — the manual will specify this. Even a low-level chirping alarm warrants outdoor fresh air and investigation.
Portable generators are the single largest cause of CO deaths during power outages. The rules are non-negotiable:
CO from a generator 3 metres from an open window can reach dangerous indoor levels within minutes. Distance and exhaust direction are not optional considerations.
| Temptation | Why It Is Deadly | Safe Alternative |
|---|---|---|
| Gas cooker for heating | Produces high CO in enclosed space | Use extra blankets; body heat; chemical hand warmers |
| Charcoal BBQ indoors | Produces lethal CO levels very rapidly | Never use indoors under any circumstances |
| Running car in garage | Fills enclosed space with CO within minutes | If warming a car, open garage door fully and never leave running unattended |
| Paraffin heater without ventilation | CO accumulates if poorly maintained or in tight space | Crack a window; never run while sleeping |
Some groups are far more vulnerable to CO poisoning:
| Item | Detail |
|---|---|
| CO sources | Gas appliances, generators, BBQs, blocked chimneys |
| Key symptoms | Headache, nausea, confusion, drowsiness |
| Multiple people affected | Strong indicator of CO — evacuate |
| Symptoms improve outside | Strong indicator of CO — do not re-enter |
| Alarm response | Evacuate all, call emergency services, medical check |
| Detector placement | Every level; outside sleeping areas; 1–1.5 m high |
| Detector lifespan | Replace entire unit every 5–7 years |
| Generator rule | Minimum 6 m from all openings; never indoors |
| Winter outage danger | Never use gas cooker, charcoal, or generator indoors |
This guide provides general information on carbon monoxide safety. It does not replace professional appliance servicing or local fire safety advice. If your CO alarm sounds, treat it as an emergency. Seek immediate medical attention for anyone showing symptoms.
Take Carbon Monoxide Poisoning Prevention with you — no internet needed when it matters most.
downloadGet on Google Play// Sources