Air, gas and the products of combustion

What you're seeing

A flame with its air supply under your control. Restrict the air and watch the products of combustion change, with carbon monoxide appearing among them. The behaviour shown is a draft awaiting review against the HSE safety action levels and the standards cited in the figure. The source link in the figure is shown as text, because artefacts can't link out.

What it shows

• Complete combustion producing carbon dioxide and water vapour
• Restricting air until carbon monoxide appears
• Why the flame picture alone is not a reliable test