Complex sentence: Intumescent seals are crucial in the fire performance of a fire resisting door set and as such the correct seal should always be used as these products differ in chemical composition, expansion rate, expansion volume and charring characteristics.
Split into simpler sentences: Intumescent seals are crucial in maintaining the performance of a fire resistant door, and as such, the correct seal should always be used. Seals may vary in chemical composition, expansion rate, expansion volume, and/or charring characteristics.