Firefighters were called to a suspected carbon monoxide leak at a house on Bedford Avenue in Hayes.
Firefighters used specialist equipment to confirm elevated readings of carbon monoxide on arrival. Two adults and two children were taken to hospital by London Ambulance Service crews.
The gas supply was isolated, and crews ventilated the property and carried out a sweep of the building to confirm that no further elevated readings were found.
A London Fire Brigade spokesperson said: “You can't taste, see or smell CO fumes, but it can kill in minutes.
"It's really important to fit a CO alarm in all rooms containing fuel burning appliances, ensuring that the alarm is able to be heard throughout your home. When sleeping, it is important that your alarm would wake you if it sounds.
"It’s also a good idea to familiarise yourself with the signs of carbon monoxide poisoning and learn what to do if you suspect someone may be affected.”
The Brigade was called at 0954 and the incident was over for firefighters by 1110. Two fire engines from Southall Fire Station attended the scene.
CO poisoning symptoms:
These symptoms also apply to your pets – so keep an eye on them too. Poisoning symptoms can easily be confused with just feeling unwell, which is why CO poisoning is so dangerous, and so often missed.