The majority of people who die in fires are overcome by smoke. A fire in a building can generate smoke that is thick and black, obscures vision, causes difficulty in breathing, and can block escape routes. The smoke will pass through any holes or gaps in the walls, ceiling and floor into other parts of the building.
Openings and service penetrations through walls or floors can quickly spread fire and should be kept to a minimum. The solum and roof space should not be forgotten. Openings and service penetrations may require to be carefully detailed and constructed to resist fire – if in doubt, check.