POSITIVE PRESSURE: NEW TESTING, NEW TERMS
By Denise Dennison, National Architectural Accounts Manager
For the past several years, the door and hardware industry has been experiencing
major changes to fire door specifications. One of the new "buzz words" in
the industry is "Positive Pressure." Along with this new testing method
comes a number of new terms including Neutral Pressure Plane, Category A,
Category B, and Intumescent.
EXACTLY WHAT IS POSITIVE PRESSURE?
Positive Pressure testing is the new method of testing fire doors in America.
As early as 1997, Positive Pressure testing was mandated by the Uniform Building
Code (UBC 7-2, 1997). With the formation of the International Code Council
(ICC), the International Building Code (IBC-2000) was developed, which also
mandates Positive Pressure testing for fire doors.
When a fire starts in a compartment, heat generates smoke and hot gases.
Fire consumes and depletes oxygen in the compartment, reducing pressure near the
fire's root or at the bottom of the room. Due to the low density and
buoyancy of the hot gases, they rise to the ceiling. When smoke and hot
gases of combustion cannot escape, they form a descending "smoke ceiling" in the
fire room. Pressure near the ceiling is greater than outside air
pressure---the pressure difference is a positive number. Pressure near the
bottom of the room is less than outside pressure---the pressure difference is a
negative number.
The compartment area where positive pressure descends and meets the negative
pressure is called the Neutral Pressure Plane. This plane is generally
horizontal; the pressure in the room becomes increasingly positive the higher it
is measured above this plane and increasingly negative the lower it is measured
below this plane. Under the old method of testing, this Neutral Pressure
Plane was set at the top of the door assembly, with the suction of cool outside
air around door edges giving the edges and the door longer survival time in the
fire test.
Full-scale room experiments have shown that the Neutral Pressure Plane occurs at
about 40 inches above the sill for door assemblies. This location is
consistent with the levels already specified in most international fire test
standards. With the Neutral Pressure Plane lowered to this level, wood
door manufacturers in the U.S. have to retest their fire doors to gain
classifications and listings for Positive Pressure-rated fire doors.
In a Positive Pressure condition, smoke and hot gases try to escape around door
edges. Without special door edge designs, enough heat is transmitted to
the unexposed face to cause its ignition and subsequent fire test failure.
To prevent the ignition of combustible door skins by hot gases escaping around
door edges, the gaps between the door edge and frame must be sealed tight.
This is achieved by chemical compounds that expand to seal these gaps, otherwise
known as Intumescents. Wood door manufacturers across the nation
now incorporate Intumescents into their door edges when necessary.
Some door assemblies may not need special Edge Sealing Systems (ESS) to comply
with Positive Pressure testing requirements. Some may not need one at
smaller sizes, but require an ESS at larger sizes or taller heights. In
order to help the Testing Agencies (Intertek/Warnock Hersey and Underwriter
Laboratories/UL) differentiate between door designs, new Listing Categories were
developed for all assembly components. Thus the birth of Category A
and Category B. Category A means the door requires no additional
ESS. Category A includes doors evaluated without an ESS between the door
and the frame as well as doors with an ESS (concealed or visible) incorporated
into/onto the edge of the door by the licensed manufacturer or machining
distributor.
Category B means the door requires an additional ESS. Category B includes
doors evaluated with an ESS field-applied to the labeled frame or door. (ESS
application does not require any machining of the frame or door.)
It is important to know which Category of fire door you are to provide.
Because Intumescents are designed to expand rapidly and with enough force to
fill the 1/8" gap between the door edges and the frame and/or the meeting edges
of pairs, there cannot be Intumescent concealed within the door and applied to
the perimeter of the frame as well. this is too much Intumescent, and the
rapid, forceful expansion could crush or buckle the core.
Wood door manufacturers continue to test for Positive Pressure requirements.
One such fire test was recently passed by Mohawk.
MOHAWK PASSES POSITIVE PRESSURE FIRE
TEST
Mohawk recently tested and passed a 20-minute fire
door burn with only one strip of paper-thin Technofire 2000 Intumescent surface
applied to the top rail, gaining the door Category A status. Previously,
Mohawk had to build the door using special Fire-Rated Composite Material for the
top rail and side stiles in order to achieve Category A status. This added
considerable cost to the the price of a 20-minute Positive Pressure rated
Category A fire door.
Mohawk's specifications now allow us to manufacture up to a 3-0 x 8-0 x 1-3/4"
single-swing door of particleboard core with basswood stiles and rails, and
surface-apply only one strip of Technofire 2000 to the top rail for 20 Minute,
Category A status. Because we burned and passed using basswood stiles and
rails, any wood exceeding the specific gravity of basswood (including fir) is
incorporated into this listing. This listing covers doors manufactured
using bonded or non-bonded construction.
This means substantial savings for 20 Minute, Category A fire doors. Any
Certified stocking distributors who presently inventory our doors with a 20
Minute stamp can machine the doors for three hinges, cylindrical or mortise
lock, a rim or mortise exit device; surface-apply the Technofire 2000
intumescent strip at the top rail; and label and supply the door for 20 Minute,
Category A openings.
With this addition, Mohawk has proven once again that product development and
innovation is truly at the forefront of our philosophy. We listen to
architects, designers, contractors, and distributors nationwide and want you to
know---we hear you! Because fire door specification is one of my
specialties, I can answer questions about fire door procedures or listings.
Please feel free to contact me at (502) 412-0410.
