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earlier edition, you’re using a code that’s some 20 years out of date, and it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 21st 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.