English Views: 0 Author: D&D HARDWARE Publish Time: 2026-06-02 Origin: D&D HARDWARE
When specifying access solutions for commercial buildings, hospitals, or multi-family housing, one question comes up repeatedly: What does UL 10C certification actually mean for a fire rated mortise lock?
As a fire door hardware manufacturer, I have seen too many spec sheets list certifications without explaining their real-world impact. At D&D HARDWARE, we believe transparency is non-negotiable. That is why every UL Listed fire rated mortise lock we produce carries File No. R40901—but let me tell you what that number truly represents.
UL 10C is not just a label. It is the difference between a door that fails under fire hose pressure and one that holds the line.
This is the first question I hear from architects and specifiers. Why does UL 10C matter if a lock already passed UL 10B?
UL 10B is known as the neutral fire test. It exposes a door assembly to rising temperatures according to a standard time-temperature curve. However, UL 10B does not include a hose stream test after the furnace exposure.
UL 10C is more demanding. It requires the same furnace test—up to UL 10C fire rated 3 hours in our case—but then adds a high-pressure fire hose blast. This simulates the thermal shock and mechanical impact of firefighting operations. A mortise lock must remain latched and fully functional after both the fire and the hose impact.
In my experience, UL 10C is the real-world standard. If a fire rated mortise lock cannot pass the hose stream test, it should not be installed in any critical egress path.
When you see UL 10C fire rated 3 hours on a product specification, it means the lock has survived three distinct phases of testing:
1.Furnace exposure – The mortise lock and door assembly are placed in a furnace where temperatures rise to over 1700°F (926°C) over three hours, following the standard time-temperature curve.
2.Flame and gas integrity – No flames or hot gases pass through the lock body or around its edges. The lock must maintain its position without deforming open.
3.Hose stream test – Immediately after the furnace, a fire hose delivers water at 30 psi (for a 2.5-inch nozzle) against the assembly. The lock cannot be blasted open.
For us at D&D HARDWARE, achieving a UL 10C fire rated 3 hours rating on our mortise locks required extensive engineering. We use high-grade stainless steel internals, precision-milled lock cases, and heat-resistant lubricants. Off-the-shelf components simply do not survive three hours plus a hose stream.
Our File No. R40901 is proof that a UL Listed fire rated mortise lock can be both reliable in daily use and life-saving in a fire.
As a dedicated fire door hardware manufacturer, I am often asked: Why not just certify for the lowest common denominator?
The answer is simple. A building’s fire door assembly is only as strong as its weakest component. The lock is the most mechanically stressed part of any fire door. If a fire rated mortise lock fails—whether due to latch retraction, case melting, or bolt deformation—the entire fire compartment is compromised.
UL 10C certification gives me confidence that our locks will perform when it matters most. That is why D&D HARDWARE has invested heavily in in-house testing capabilities and third-party validation through UL.
We do not chase shortcuts. We chase UL 10C fire rated 3 hours ratings because building occupants deserve real protection.
File No. R40901 is not just a file number. It is our commitment.
Many people underestimate the hose stream test. Let me explain why it is brutal.
After three hours of furnace heating, the fire rated mortise lock and door are glowing hot. The metal is weakened. The latch mechanism may be close to its tolerance limits.
Then, a fire hose delivers water at high pressure. The sudden cooling creates thermal shock. The water pressure pushes directly against the lock and door.
If the UL Listed fire rated mortise lock has any design flaw—brittle springs, weak latch bolts, thin case walls—it will fail. The latch may retract. The case may crack. The door may swing open.
I have witnessed tests where non-certified locks failed in under 30 seconds of the hose stream. Our UL 10C fire rated 3 hours mortise locks remain fully latched. That is the difference between containment and disaster.
No. And I want to be very clear about this.
A fire rated mortise lock with UL 10C certification is tested as part of a specific door assembly. That includes the door material (wood, steel, or composite), the frame, the hinges, and the lock itself.
However, because UL 10C is the most widely adopted standard for positive-pressure fire testing in North America, a UL Listed fire rated mortise lock with File No. R40901 is accepted for most commercial applications that require 3-hour fire ratings.
Always check local codes. But when specifiers see UL 10C fire rated 3 hours on our documentation, they know we have done the heavy lifting.
D&D Hardware: Your Certified Partner for Fire-Rated Door Solutions.
NFPA 80 (Standard for Fire Doors and Other Opening Protectives) explicitly requires that fire door hardware be tested and listed according to UL 10C or an equivalent positive-pressure fire test.
In practice, this means:
•A fire rated mortise lock without UL 10C certification cannot be installed on a labeled fire door assembly in most jurisdictions.
•Authorities Having Jurisdiction (AHJs) will look for the UL mark and file number.
•File No. R40901 provides traceability back to our factory and testing records.
As a UL fire door hardware manufacturer, we maintain full traceability from raw material to finished UL Listed fire rated mortise lock. That is not just good manufacturing—it is code compliance.
1. Is UL 10C required for all fire rated mortise locks?
Not all, but for 3-hour rated doors in commercial buildings under NFPA 80, yes. Local codes vary, but UL 10C is the gold standard for positive-pressure fire testing.
2. What is the difference between UL 10C and UL 10B for mortise locks?
UL 10B is a neutral fire test without a hose stream. UL 10C includes the hose stream test, making it more realistic for modern building fire conditions.
3. Does D&D HARDWARE offer UL 10C fire rated 3 hours mortise locks?
Yes. Our UL Listed fire rated mortise lock carries File No. R40901 and is certified for UL 10C fire rated 3 hours.
4. Can I replace an existing mortise lock with a UL 10C certified lock on a fire door?
Yes, provided the replacement lock is listed for the same fire rating and door type. Always consult the door manufacturer’s listing. Our File No. R40901 documentation specifies compatible door assemblies.
5. Why should I choose a fire door hardware manufacturer like D&D HARDWARE?
Because we specialize in fire rated mortise locks with UL 10C certification. We are not a general hardware supplier. We are D&D HARDWARE, a dedicated fire door hardware manufacturer with File No. R40901 and a commitment to passive fire protection.
I do not treat UL 10C certification as a marketing checkbox. When a building owner, architect, or contractor chooses a UL Listed fire rated mortise lock from D&D HARDWARE, they are trusting us with life safety.
That trust is backed by File No. R40901, by UL 10C fire rated 3 hours testing, and by our identity as a fire door hardware manufacturer that refuses to compromise.
Whether you are designing a high-rise stairwell or a hospital corridor, remember: The lock is the last line of defense. Make sure it is certified for the job.
D&D Hardware: Your Certified Partner for Fire-Rated Door Solutions.
Contact: David Jian
Mob:0086-139 2903 7292
Email: David@dndhardware.com, sales@dndhardware.com,
Contact: Jobby Zhang
Mob:0086-137 2599 9617
Email: jobby@dndhardware.com
D&D HARDWARE INDUSTRIAL CO.,LTD
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