How to determine the required fire protection rating of an opening protective?
Depending on the construction type and use, buildings may be designed and constructed with fire resistance-rated walls, floors and ceilings for structural integrity as well as to prevent fire and smoke from spreading throughout the building. However, openings in these fire rated assemblies are necessary for egress, communication, security, everyday travel throughout the building, and building services and equipment. Openings in fire rated assemblies must be protected accordingly so as to not compromise the fire resistance of the assembly in which they are located. Unprotected or improperly protected openings can void the rating of the wall, floor or ceiling by leaving ways for fire and smoke to spread unintentionally to adjacent fire compartments.
Fire rated components in buildings have either a fire resistance rating or a fire protection rating. It is important to understand the difference in the two ratings and to understand how to determine the required ratings of assemblies both when designing a building and also when determining compliance of existing installations. Although often used interchangeably, the terms are different.
Fire resistance rating vs. fire protection rating
When a building assembly, such as a fire barrier, is required to be fire rated it must be reasonably airtight under increased air pressure on the fire side due to heated air expansion and must prevent the passage of heat and flame for a designated time. Fire barriers also must be capable of withstanding direct impingement by the fire, as determined by large-scale tests, either ASTM E119 or ANSI/UL 263. The ASTM E119 and ANSI/UL 263 test standards determine fire resistance ratings, in hours, based on exposure to the standard time-temperature curve and provide the rating of the construction of the particular assembly and the actual testing of the assembly in the test furnace.
Assemblies protecting openings, such as doors and windows, located in fire resistance-rated assemblies must be capable of withstanding the effects of fire, as determined by large-scale tests such as NFPA 252, NFPA 257, ANSI UL10B, ANSI/UL 10C or ANSI/UL 9. The acceptance criteria for these fire protection-rated assemblies, differ from those for fire resistance-rated construction, such as a wall or floor/ceiling assembly. The limitation of temperature rise through a fire door is not normally a measure of acceptance, although it is a measure of acceptance for a fire resistance–rated assembly such as a wall.
Some openings may also be protected with products that have a fire resistance rating where they have been tested as, and passed criteria as required for walls, floors or ceilings. Fire resistance rating, glazing, is an example of this. It may be installed and used as a wall in some cases if permitted and tested accordingly.
Determining the required fire protection rating
To properly protect an opening in a fire resistance-rated assembly, the proper fire protection rating is required. The following steps should be followed when determining the appropriate fire protection rating of an opening protective:
Step 1: Determine the required fire resistance rating of the component under evaluation. Components include, but are not limited to, vertical shafts, horizontal exits, exit access corridors, and smoke barriers. Codes, such as NFPA 101, Life Safety Code, NFPA 5000, Building Construction and Safety Code, mandate where a building component is required to have a fire-resistance rating.
Step 2: Utilize the tables, “Minimum Fire Ratings For Opening Protectives in Fire Resistance-Rated Assemblies and Fire-Rated Glazing Markings”, found in Chapter 8 of both NFPA 101 and NFPA 5000 to determine the minimum fire protection rating of the opening protective based on the fire resistance rating determined in Step 1. It should be carefully noted that this table DOES NOT mandate the fire resistance ratings of components, other provisions in the Code will require it.
Step 3: Confirm through footnotes, other code text associated with the component, and through occupancy specific provisions, that no further modifications to the general fire protection ratings are permitted. In some cases, there may be exemptions for some opening protectives in existing installations or for certain conditions in some occupancies.
Let’s look at an example: What is the required fire protection rating for a corridor door in an exit access corridor in a new, non-sprinklered, office building?
Per NFPA 101, most new, non-sprinklered, business occupancies require exit access corridors have a minimum 1-hour fire resistance rating (step 1). Next, by going to the referenced table in NFPA 101 (table 184.108.40.206.2) it can be determined that a 1-hour fire resistance-rated exit access corridor requires a minimum 1/3-hour, or 20-minute, fire-protection-rated door. It can then be confirmed that no further modifications are permitted (step 3).
Why can the fire protection rating be less than the fire resistance rating?
The required minimum fire protection ratings of opening protectives are sometimes permitted to be of a lower rating than the fire resistance rating of the fire barrier in which they are located. For example, a 2-hour fire barrier enclosing an exit stair is permitted to have fire doors protected by 1½-hour fire protection-rated door assemblies. The test procedures on which the ratings are based, discussed above, are different. Although combustibles placed against a fire resistance–rated wall expose the wall to a considerable fire challenge, a fire protection-rated door assembly does not usually have combustibles placed against it, because the opening must be clear to use the door and kept free of obstructions for proper operation of the door. Such a scenario suggests that, if a door is not to be used and combustible storage is to be placed at the door opening, the door should be removed and the opening replaced with solid construction to restore the wall to its required fire resistance rating.
Fire rated components are a critical piece to the comprehensive protection strategy that buildings use to protect people and the building itself from the effects of fire. The success of passive fire protection methods such as the use of compartmentation requires careful compliance during design and installation as well as effective and consistent inspection, testing and maintenance to ensure the system will perform as intended during a fire.
What challenges have you faced when designing buildings with fire rated components? In what role have you worked with applying code requirements for opening protectives? Please share your feedback in the comments below!