The importance of penetration seals cannot be overstated. Experience shows that penetrations tend to be the weakest link in the chain of compartmentation within buildings. We should all be aware that in such building compartments the most likely threat from the spread of fire will occur where services penetrate walls or floors, or where concealed cavities between separating elements interlink. Unfortunately, the lack of seals, incorrect specification and incorrect installation has contributed to many large fires in all buildings, both new and old, which would not have been so destructive if the penetrations through compartment walls and floors had been adequately sealed against the passage of fire and smoke, or that seals had been properly specified.