Fire doors rating

Fire doors rating

Definition of a Fire Door - a door assembly, which is designed to hold back fire and smoke for a designated period and has been tested under conditions for door assemblies described in British Standard 476 Part 22; Fire Door Guidance -British Standard 8214-2008 (Code of Practice for Fire Door Assemblies).

Fire doors are made up of various components. The door itself is usually made from a solid timber frame, but they can sometimes be covered again in fire-resistant glass.

When I’m asked, “What is the required rating for a door in a particular wall?” nine times out of 10 my answer is, “It depends.” (This is the standard answer for nearly everything code-related.) In the Life Safety Code, required ratings for doors and other opening protective (e.g., windows) depend on the required hourly, fire-resistance rating of the barrier in which the opening is located and the function the barrier is serving.

Not all fire barriers are created equal. A door in an exit enclosure fire barrier will probably require a different rating than a door in a similarly rated corridor or hazardous area enclosure. Or a smoke barrier. Or a smoke partition. Or a shaft enclosure. (You get the idea.) At first glance it may seem convoluted, but the code does a good job of consolidating the opening protective rating requirements in one location. In the 2018 edition, you’ll find the required door rating in Table 8.3.3.2.2 (what I’ll refer to as “the table”). In the 2015 and earlier editions, the required ratings were located in Table 8.3.4.2. Prior to the 2003 edition, there was no handy consolidated table. If you’re using the 2000 or earlier edition, you’ll have to sort through a series of requirements and exceptions to determine the required door rating. (If you’re using the 2000 or earlier edition, you’re using a code that’s some 20 years out of date, and it might be time to join the rest of us in the 21^st century. But I digress.)

To use the table, you’ll first need to establish the fire barrier’s purpose as required by the code. The table lists the purpose under the heading “Component.” Components include:

• ·        Elevator hoistways
• ·        Elevator lobbies
• ·        Vertical shafts
• ·        Horizontal exits
• ·        Exit access corridors
• ·        Other fire barriers
• ·        Smoke barriers
• ·        Smoke partitions

This is where the table has, at times, caused some confusion. Some have misinterpreted it as prescribing minimum fire-resistance ratings for various fire barriers. For example, the bottom row addresses smoke partitions. The second column specifies fire-resistance ratings for smoke partitions (half hour and one hour). Some have been led to believe that based on the table, all smoke partitions must have a minimum fire resistance rating of a half hour. This is not the case for smoke partitions or any of the other components listed in the table.

How can I find out more about an existing fire door?

Each fire door is labeled with a permanent label that must remain legible. Fire-rated frames may have a label or embossment from a listing agency. The door and frame labels contain a wealth of information, including the manufacturer, length of time the component is designed to resist fire, whether the opening is to be equipped with fire exit hardware, and whether the door carries a temperature rise rating or is a smoke door assembly.

Fire door labels usually include a number allowing manufacturers to access more information about the door’s original construction. Frame labels may state a fire resistance duration longer than that of the door. In this case, the assembly’s rating will be the lower of the two. Some hardware, such as fire exit hardware, will also be labeled, but the information on the label is typically less detailed.

The requirements for smoke partitions are located in Section 8.4; you’ll find no fire-resistance rating requirement there. Smoke partitions require a rating only where required by another section of the code. An example would be corridor walls in new, large, residential board-and-care occupancies, which require a half-hour rating (32.3.3.6.2). Once it’s determined that the smoke partition requires a fire-resistance rating, then refer to the table to determine the required fire-protection rating of any doors. In the case of a half-hour rated smoke partition, doors must have a one-third hour, or 20 minute, fire-protection rating. In short, use the table to determine the required opening protective rating when a barrier is required by another section of the code to have a fire-resistance rating.

Fire barriers having a one-hour rating might require one-hour doors, three-quarter-hour doors, or one-third-hour doors. Again, it depends on the barrier’s application. Fire barriers having a two-hour rating generally require one-and-a-half hour doors. Fire barriers with a rating exceeding two hours are rarely required by the code, except for a few occupancy separation fire barriers involving relatively hazardous occupancies.

I sometimes get the question, “Why does the code allow a 20-minute door in a one-hour barrier? Why not just require a one-hour door?” This would certainly make life easier when applying the code, but it also might require a more expensive door than is actually needed for life safety. Where the code requires 20-minute doors, it’s usually in a barrier that the committees primarily wanted to be smoke resistant. Before the days of smoke partitions, which first appeared in the 2000 edition, when a committee wanted a smoke resistant barrier (e.g., a corridor wall), it was simpler to mandate a one-hour barrier than to come up with criteria to evaluate smoke resistance. Since they really wanted a nominal degree of fire resistance, rather than mandating a substantial one-hour door, they were comfortable with a 20-minute door, which would inherently resist the passage of smoke.

Other reasons for the difference in fire barrier ratings and door ratings are the tests used to establish the ratings. You might have noticed I refer to the fire-resistance rating of a fire barrier, whereas a door has a fire-protection rating. Fire barrier assemblies are tested at a lab using a standard like ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, which yields a fire-resistance rating. Fire doors are tested using a standard like NFPA 252, Standard Methods of Fire Tests of Door Assemblies, which yields a fire-protection rating. Comparing the ratings from the different tests is not an apples-to-apples comparison. An hour’s worth of fire resistance (fire barrier) is not necessarily equivalent to an hour’s worth of fire protection (fire door).

And although it’s not a very scientific reason, this is the way the code has done it for many years and it seems to work. To this point, there has been no compelling reason to change the approach. If it’s not broken, there’s no need to fix it.

Remember Fire resisting glass can withstand exposure to the heat condition in a fire test for at least 60 minutes before it reaches a temperature high enough to soften it. This is mainly because, with clear FR glazing, nearly 50 per cent of the incident heat is transmitted through the glass by radiation.

Where can I find the code requirements for fire doors?

National Fire Protection Association (NFPA) 80, Standard for Fire Doors and Other Opening Protectives, is referenced by the International Building Code (IBC), International Fire Code (IFC), NFPA 101, Life Safety Code, and other codes and standards. NFPA 105, Standard for the Installation of Smoke Door Assemblies and Other Opening Protectives, addresses smoke doors and is also referenced in these publications.

Some fire door requirements are included within the applicable building or fire code, but NFPA 80 and 105 are referenced for many of the detailed requirements. For product-specific issues, the manufacturer’s listings must be referenced. For example, to find out the maximum fire door size available from a particular manufacturer,

The increased use of sprinklers has resulted in reduced requirements for temperature-rise doors. The 2012 IBC requires doors in interior exit stairways/ramps and exit passageways to have a maximum transmitted rise in temperature of 232 C (450 F) above ambient at the end of 30 minutes of exposure, but also includes an exception stating temperature-rise doors are not required in buildings equipped throughout with an automatic sprinkler system.

For the convenience of building occupants, how can fire doors be held open in a code-compliant manner?

Fire doors must be closed during a fire to compartmentalize the building and prevent the spread of smoke and flames. The intent is to protect the means of egress and allow building occupants time to evacuate safely. If fire doors are blocked or wedged open, they will not be able to do their job and protect the building and its occupants.

What is positive-latching, and is it required for all fire doors?

Hardware on fire door assemblies has to have an active latchbolt to prevent the pressure caused by a fire from pushing the door open and allowing smoke and flames to spread. A springlatch found in a standard lockset or latchset is considered an active latchbolt; some fire door configurations require a specific ‘latch throw’ (i.e. dimension of latch projection).

A deadbolt is not an active latchbolt, because it can be held retracted. An electromagnetic lock does not provide a positive latch, because there is no latching mechanism and the locking is accomplished when the electromagnet bonds to the steel armature. Electric strikes used on fire doors must be fail-secure—that is, when power is cut, the latch is securely captured behind the strike keeper. A fail-safe electric strike could allow the door to become unlatched, so such strikes may not be used on fire doors.

How is fire exit hardware different from panic hardware?

When panic hardware is used on fire doors, it must be fire exit hardware, which bears labels for both panic and fire resistance. A door with fire exit hardware will also have an additional label, indicating it is equipped with fire exit hardware. Fire exit hardware does not incorporate a mechanical dogging feature—the means to hold the latch retracted using a key, thumbturn, or Allen wrench. For fire doors where a ‘push/pull’ condition is desired, fire exit hardware with electric latch retraction may be used, as long as the latch projects automatically upon fire alarm, to secure the door.

Some vertical rod fire exit hardware for pairs of doors can be installed ‘less bottom rod’ (LBR). These devices use the top rod and latch only, with no bottom rod or latch. The advantage is there is no floor-mounted strike, and no bottom rod or latch to become damaged by carts or traffic. This configuration can sometimes cause a reduction in security, because it may be more easily defeated with only one latching point at the top of the door. In most cases, doors with LBR devices are required to have an auxiliary fire pin, which mounts in the edge of one door and projects into a hole in the edge of the other door if there is a fire.

Do fire doors need smoke gasketing? Are smoke doors also fire doors?

NFPA 80 and NFPA 105 do not specifically state fire doors and smoke doors require smoke gasketing. The key is to check the applicable code or standard, such as the International Building Code, for a limitation on air infiltration, typically a reference to UL 1784, Air Leakage Tests of Door Assemblies, as the test standard.

For fire doors and smoke doors in certain locations, the limit for air infiltration is 0.02 m3/(s • m2) or less as tested at a pressure of 0.02 kPa (3 cfm per square foot or less as tested at a pressure of 0.10 inch of water)—for most door sizes, this cannot be achieved without smoke gasketing. The requirements for smoke doors and fire doors depend on where they are used. For example, smoke barriers, smoke partitions, exit enclosures, and corridors all have varying requirements for smoke and fire resistance, and the applicable code sections must be consulted to see if a limit on air infiltration is established.

Thanks for reading, and as always, stay safe.