Understanding the Difference Between UL 10B vs. UL 10C

What Is the UL 10B Fire Test?

First introduced by Underwriters Laboratories in 1962, the UL 10B fire test is regarded as the gold standard fire test, and, despite being over sixty years old, is still used today. The important differentiation here is that the UL 10B fire test evaluates a door assembly’s capacity to withstand fire under neutral or negative conditions.

In layman’s terms, this is “static” conditions, where smoke and heat are not artificially forced through gaps. The test is pretty straightforward: the door is placed in a furnace and then hosed down with a standard fire hose. It is then inspected to see how its structural integrity held up. The door takes a lot of punishment, and if it can withstand the heat and the hose-down, it will pass. Naturally, it’s more involved than that, but that’s the brass tacks explanation.

Modern codes call for positive pressure tests, like the UL 10C, the UL 10B fire test is still used in legacy installations or in regions or specific situations where the older code references remain in place. Understanding the UL 10B fire test helps project teams match the correct certification requirements. This is why understanding fire safety certification differences is essential to the workflow of design teams.

What Is the UL 10C Fire Test?

In a much-needed upgrade, Underwriters Laboratories introduced UL 10C in 1998. Developed to address modern building codes, the UL 10C fire test provides a much more natural simulation of how fire actually behaves. Instead of the “static” test of the UL 10B fire test, the UL 10C fire test takes place under positive pressure during the burn phase.

Hot gases and smoke are actively pushed through gaps, which is how fire commonly behaves in real-world situations. In the UL 10B vs UL 10C discussion, fire safety differences come down to application. Different fire-rated door testing standards depend on where the installation takes place, and the UL 10C standard will be implemented in new commercial, institutional, and high-occupancy projects.

UL 10B vs UL 10C: Key Differences

One of the most significant differences between the UL 10B fire test and the UL 10C fire test lies in how they affect door construction and hardware.

Under UL 10C’s positive pressure conditions, the heat and smoke are forced toward the unexposed side of the door, putting immediate stress on seals, intumescent strips, hinges, latches, and glazing systems.

Weak points are revealed quickly: seals may warp, latch mechanisms can distort, and glazing beads may fail, allowing smoke or flame penetration. Passing a UL 10C fire test often requires upgraded materials, reinforced frames, and precision installation to maintain performance under this pressure. In some projects, even surface finishes and films are selected for their fire-resistant properties to ensure they don’t undermine the door’s rating.

By comparison, UL 10B’s neutral or negative pressure environment is less punishing on these components. Doors that pass UL 10B may still meet specific local codes, but they could underperform in an actual positive-pressure fire scenario. For manufacturers, installers, and inspectors, this distinction matters: a product designed for UL 10C compliance is inherently built to withstand harsher, more realistic fire conditions, making it a safer choice for most modern applications.

Why the Difference Matters for Your Project

Choosing the correct fire-rated door testing standards isn’t just a paperwork exercise — it can determine whether a project passes inspection, meets insurance requirements, and protects occupants in a real fire. Installing a door tested only to UL 10B in a jurisdiction that requires UL 10C could result in costly retrofits, delays, or outright rejection by building control.

When it comes to safety, the UL 10C fire test has the edge. Its positive-pressure conditions do a better job of showing how a door will actually behave when modern fire dynamics come into play. That kind of extra performance can make a world of difference in high-risk environments.

Material compatibility also plays a role. Surface finishes, vision panels, and even window films must not undermine a fire door’s performance. This is where M1-rated products, such as SolarScreen’s architectural films, can help maintain compliance — delivering the desired design or energy-control benefits without adding fuel to the fire.

Integrating Fire Safety Into Material Selection

A door that passed its UL 10C test with flying colours can have its rating compromised by making the wrong choices in component parts. Glazing, hardware, and surface materials all have to stand up to the test to pass. Some materials can ignite easily, emit smoke, toxic fumes, or even totally degrade. All this can severely undermine the assembly’s performance during a fire safety test.

That’s why a lot of designers go for materials that tick the boxes for looks and performance and help with fire safety compliance. Under European standards, an M1 fire-resistance rating means the product is tough to ignite and won’t do much to feed a fire if one breaks out.

The Bottom Line

Whether the job calls for UL 10B or UL 10C, knowing what each test demands is the best way to stay on the right side of safety. Pairing the right door rating with fire-rated finishes, like M1-rated films, keeps performance, looks, and compliance working together.

For more on integrating fire safety into your material choices, there are many resources on Solar Screen’s blogs.