What CO in room air means, why an analyser can find it before an alarm sounds, and how to protect people first.
Room air is a different measurement
CO is expected in a flue-gas sample, which is judged against the appliance's combustion criteria. The room air people breathe should be essentially free of it. Flue limits cannot be applied to room air, and any meaningful CO in the living space is a danger signal in its own right. Possible sources include spillage, a leaking flue or case, a poorly burning flueless appliance, another fuel-burning device or fumes entering from elsewhere. The reading does not tell you where the CO came from, or when. CO does not settle at floor level; it mixes through the room.
Protect people first
Suspected CO exposure calls for prompt action. Do not wait for a generic room-air concentration band or a domestic alarm before deciding people need help.
- If an occupant reports headache or nausea that improves outside, stop the work, get everyone into fresh air and obtain medical and emergency advice. Do not re-enter until advised it is safe.
- Call NHS 111 for suspected CO symptoms. Call 999 for breathing difficulty, sudden confusion, loss of consciousness, weakness, or chest or muscle pain. Do not drive yourself to A&E.
- For a suspected gas-appliance CO incident in Great Britain, also call 0800 111 999 from safety. The emergency gas call does not replace medical help.
Reading the trend
- Readings rise while a suspect appliance runs: stop the test, cease operation, get occupants into fresh air and ventilate, then follow the applicable make-safe and reporting procedure.
- Readings repeat with no symptoms: stop the test and get occupants into fresh air. Ventilate if safe and prevent further use of the suspect appliance. Seek the appropriate emergency advice and arrange investigation of the source and possible migration routes; a silent alarm, or a reading that falls after ventilating, does not tell you the cause.
- CO present while the appliance you came to check is off: it may remain from earlier operation or be entering from another source. Protect people and investigate the operating history, other appliances and possible migration routes. Do not dismiss the reading or assume that switching off and ventilating has resolved the cause.
Room CO tests on an analyser
Analysers run room CO tests as timed presets. On the KANE458s, for example, a general test, a migration test, a type B open-flued boiler and a type C room-sealed appliance each run for 15 minutes, a type A cooker or space heater for 30 minutes, a type A water heater for 5 minutes and a sweep test for 2 minutes, storing a result every minute. Every preset uses a 10 ppm limit and a 30 ppm alarm.
Analyser versus alarm
A measuring instrument can detect lower CO levels than the point at which a domestic alarm is designed to sound, because alarms react to higher or more sustained levels. A reading below the alarm's trigger still needs attention, and a silent alarm does not mean the analyser is faulty. An alarm is a useful last line of warning, never a substitute for combustion checks.
After the event
A later low reading after ventilation does not rule out earlier exposure. Correct the cause and complete the required safety checks before a suspect appliance goes back into use.