PFP systems are designed to "prevent" the spread of fire and smoke, or heating of structural members, for an intended limited period of time as determined by the local building code and fire codes. Passive fire protection measures such as firestops, fire walls, and fire doors, are tested to determine the fire-resistance rating of the final assembly, which is usually expressed in terms of hours of fire resistance (e.g., ⅓, ¾, 1, 1½, 2, 3, 4 hour). A certification listing provides the limitations of the rating.
