Carbon Monoxide — Symptoms & Immediate Response

Carbon monoxide (CO) is colourless, odourless, and tasteless. You cannot detect it without an alarm. It is produced by the incomplete combustion of gas, oil, wood, charcoal, and petrol — including boilers, heaters, generators, and barbecues.

⚠️ CO kills quickly. If your alarm sounds, or if multiple people in the same space develop similar flu-like symptoms without fever — treat it as CO poisoning and act immediately.

Symptoms by Severity

Mild Exposure

Symptoms often come and go, or improve when you leave the building.

Symptom	Notes
Headache	Often the first and most common symptom
Dizziness or lightheadedness	Worsens on physical activity
Nausea	Without vomiting in mild cases
Shortness of breath	On exertion
Tiredness or confusion	May be mistaken for flu

Key clue: Symptoms improve outdoors and return when you go back inside.

Moderate Exposure

Symptom	Notes
Throbbing headache	More severe
Drowsiness	Difficult to stay awake
Vomiting
Rapid heart rate
Difficulty thinking clearly	Impaired judgement — may delay your own escape

Severe Exposure — Emergency

Symptom	Action Required
Confusion or disorientation	Call 999/911 immediately
Chest pain	Call 999/911 immediately
Seizures	Call 999/911 immediately
Loss of consciousness	Call 999/911 immediately
Breathing difficulties	Call 999/911 immediately

Immediate Response Steps

Step	Action
1. Move outside immediately	Get everyone (including pets) into fresh air — do not stop to collect belongings
2. Call emergency services	999 / 911 — tell them you suspect CO poisoning
3. Do not re-enter	Even if you feel better outside — CO may still be present
4. Leave door open if safe	Helps ventilate
5. If someone is unconscious	Open airway; check breathing; begin CPR if needed; do not move them back inside
6. Seek medical attention	Everyone exposed should be assessed — even those with mild symptoms

Unconscious Person — CO Poisoning

1. Move them to fresh air if you can do so safely — do not put yourself at risk
2. Call emergency services immediately
3. Open airway: tilt head back, lift chin
4. If not breathing: begin CPR (30 compressions : 2 breaths)
5. If breathing: place in recovery position
6. Stay with them until emergency services arrive

Common Sources of CO

Source	Risk Scenario
Gas boiler or furnace	Blocked flue, poor maintenance, incomplete combustion
Open fire / wood burner	Blocked chimney, damp wood, inadequate ventilation
Portable generator	Indoors or near open windows — never use inside
BBQ or charcoal	Never use indoors or in enclosed spaces including tents
Gas cooker	Extended use without ventilation; never use for space heating
Car engine	Running in a garage — even with the door open
Petrol-powered tools	Pressure washers, lawnmowers used in enclosed spaces

⚠️ Never run a generator, barbecue, or petrol engine indoors or in a garage, even with the door open.

Alarm Sounded — What To Do

1. Do not try to find the source
2. Get everyone out immediately
3. Leave the door open on the way out
4. Call 999 / 911 from outside
5. Do not go back in until fire and rescue service say it is safe
6. Call a Gas Safe registered engineer before using any appliances again

Quick Reference

Situation	Action
CO alarm sounds	Evacuate immediately; call 999/911 from outside; do not re-enter
Flu-like symptoms, multiple people, no fever	Suspect CO; get outside; call 999
Symptoms improve outdoors	Strong sign of CO — do not return inside
Person unconscious from CO	Fresh air; CPR if not breathing; call 999 immediately
Generator or BBQ indoors	Do not — CO accumulates fatally within minutes
Re-entry after alarm	Only when fire and rescue declare it safe