Best Practices for Thresholds, Weatherstripping, and Fire Safety by Dan White

This article appears in the June issue of the DHI Security + Safety Magazine and is reprinted here with their permission.

An array of products installed in commercial buildings affect life safety, many of which require a UL listing. While not the largest or most glamorous materials, thresholds, weatherstripping, and gasketing products serve as barriers to fire and smoke inhalation, and while small in size, they are some of the biggest contributors to preserving life.

What is the UL Label?
Underwriters Laboratories, LLC (UL) has been around for more than 125 years and is known across multiple industries as a leader in global safety. Their simple mission, “Working for a safer world since 1894,” is at the core of everything they do. According to their website, “We conscientiously advance safety science through careful research and investigation, applying our efforts to prevent or reduce loss of life and property and to promote safe living and working environments for all people.”[1]

UL certifications can be found on hundreds of building material products, including door assemblies. “Our fire safety team evaluates a wide range of products for fire resistance and performance, including door frames, locks, closers, hinges, and other door accessories,” notes the UL website.[2]

UL as It Applies to Fire Door Inspections
NFPA 80: Standards for Fire Doors and Other Opening Protectives covers the installation, care, and maintenance of many types of fires doors and opening protectives. Specifically, this code requires that all fire door assemblies be inspected and tested annually. The inspector will check the door for a number of items pertaining to functionality and fire safety, as well as for the UL label – signifying the product has passed the UL10C testing standard.

What’s important to note is that for certain door opening components, the UL label is not required to be on the product. For kick plates mounted below 16”, thresholds and weatherstripping, the UL rating is instead on the packaging. Therefore, during an inspection, because a visible UL label is not on these products as they are on doorframes, wood doors, door closers or latches, this can trigger a request for additional documentation to ensure UL ratings. The building owner is wise to have this documentation on file so the fire inspector can easily review and compare the installation to the standard.

However, even though the UL10C test standard was originally created through collaboration with UL, any accredited Third Party Nationally Recognized Testing Laboratory (NRTL) can perform the UL10C test and apply a label. Case in point, some manufacturers use Intertek as their listing agency; therefore, products may be labeled by UL and Intertek (ETL)

Smoke & Fire Testing
The job of weatherstripping and thresholds is two part. The obvious job – and the one that most people think about – is that it blocks drafts, dirt and provides a sound barrier. The second job – the one many in our industry would argue is the more important one – is its job is to prevent smoke and fire from traveling from one compartment to the next, as smoke inhalation is the main cause of death in a fire. The job of these products, in short, is to save lives.

Inspectors test several areas of infiltration on an opening, such as temperature, sound, water (in hurricane-prone states), smoke and fire. Let’s take a closer look at the testing for smoke and fire infiltration.

“When it comes to fire, thresholds are not required unless it is a pressurized compartment, such as a stairwell in a high-rise building,” explains Brian Clarke, AHC, CDT Director, Architectural Specifications for Hager Companies. The NFPA standard allows for ¾” clearance at the bottom of a fire or smoke door as long as it is not a pressurized compartment.

Thresholds are tested to the UL10C – the Standard for Positive Pressure Fire Tests of Door Assembly. “During a fire, the ultimate goal is that the door is able to stay closed and that the fire stays on one side of the door,” explains Mark McRae, Director of Engineering for Hager Companies. In basic terms, the UL10C test looks at the materials used in the door assembly and whether or not they sustain a flame for five seconds or less – which the standard allows.

In the case of fire and smoke testing, the door assembly must meet UL10C and UL1784 – the Standard for Safety Air Leakage and Door Assembly.

“When it comes to smoke, seals are tested by how much smoke penetrates in the first 20 minutes,” notes Brian. “Unfortunately, after 20 minutes, a person will die from smoke inhalation.”

An example of press-on weather strip that would be tested in the Smoke and Draft Test/Category H – a test for smoke that does not involve fire. This product controls the smoke from going from one side of the door to the other.

“In the case of thresholds, too many people don’t give them a lot of thought. Besides ensuring that dirt and debris stay on the outside, they are also a critical component to life safety in the event of a fire,” notes Ginny Powell, Product Marketing Specialist for Hager Companies.

Weatherstripping & Gasketing Products
Doors and frames may be “fire rated” for a set amount of time, from 20 minutes up to 180 minutes, but it is important to note that at the end of the test, the product will not be intact. Weatherstripping is a silicone, neoprene or vinyl insert housed in aluminum. It may be fire-rated for 90 minutes, but the product will not be there after a fire test. It will melt. What is key to the test is that it does not impede the door or the frame passing the test.

There are three different categories of weatherstripping – all of which relate back to what happens to the weatherstripping during a fire: Fire Test | Category J: These products do not contribute to flaming during a fire. Examples are gaskets used for sound, draft control or automatic door bottoms.

  • Fire Test | Category J: These products do not contribute to flaming during fire. Examples are gaskets used for sound, draft control or automatic door bottoms.
  • Smoke and Draft Test | Category H: This is a separate, second test for smoke that does not involve fire. These products control the smoke from going from one side of the door to the other.
  • Fire Test| Category G: This product is a gasket with an edge-sealing system, usually manufactured with intumescent materials, meaning this material will swell to many times its original size during a fire and help contain the spread of fire by sealing the edges of the door.

New and existing fire doors are classified/labeled by one of the following designation systems: hourly rating, alphabetical rating or a combination of both (as the chart illustrates). The manufacturer’s specifications will detail the fire rating and best uses.

Following the manufacturer’s instructions is just as crucial to maintain the integrity of the seal as is the product itself. “Some specs require a continuous seam all the way around the opening, so the installer needs to be careful not to cut or notch the seal, as those will create gaps,” says Brian.

For example, in an aluminum-extruded smoke seal, the product needs to either be wide enough to allow for the surface-supplied hardware to be attached or brackets must be supplied to mount over the seal so the surface mounted hardware can mount to it. In either case, the template needs to be adjusted for the products that have surface mounted components. “One of the most common mistakes we see made is not adjusting for this when ordering doors,” says Brian. “The door cannot be modified out in the field because it is fire rated, and their answer is to just cut the seal. When you do this, the seal is now going to fail inspection.”

A UL listed meeting stile astragal used to seal a gap

A Door Isn’t Just a Door
Throughout the door and hardware industry, we are known to say that a door isn’t just a door. It’s about the life and safety of people. It is definitely the case when it comes to smoke and fire. When you have the right products on the opening, something as simple as a gasket can make all the difference between life or death.

Press-On Weatherstripping Best Practices:

[1] Source:

[2] Source:

Dan White is a product development manager
and can be reached at [email protected]