Fire needs three things at the same time: an ignition source, fuel and oxygen. The assessor works through the building asking where those three sit close enough together to matter. An electrical intake cupboard is an ignition source; the same cupboard with cardboard stacked inside it is an ignition source pressed against fuel, and a different order of problem. What are some examples of fire hazards catalogues the combinations that recur across UK housing.
Breaking any side of the triangle prevents fire, but in practice most prevention effort lands on the first two: keeping ignition sources maintained, secured and separated, and starving potential fires of fuel through housekeeping, storage rules and the choice of materials. Oxygen is ambient and cannot usefully be controlled in a home, which is why it matters most for spread: open doors, breached compartmentation and unstopped service penetrations decide how far a fire travels once prevention has failed.