The Condenser - Understanding the Fire Resistance Rating

Every fire damper and fire smoke damper will have a fire resistance rating. What does the rating mean? Learn about the tests and standards with this quick Condenser article.

The Importance of Passive Fire Protection

Passive fire protection contains and slows the spread of fire through a building. This protection will consist of fire barriers that make up compartments in the building. Each component is tested to strict standards to determine whether it can endure a fire event.

Fire dampers are installed in fire barriers to prevent flames from passing through HVAC penetrations in the barrier, like vents and ducts. They must close at the first signs of a fire. Once closed, they must remain intact to keep the penetration covered. The damper’s fire resistance rating will help determine its longevity.

For more on dampers, check out these Newsstand articles:

• The Condenser - Temperature Limits for HVAC Dampers
• HVAC Damper Control - Automation Equipment for Dampers
• Connecting Dampers and Multi-Panel Assemblies

Fire Resistance Ratings

The fire resistance rating refers to the damper’s capabilities to endure flames. There are two ratings for fire dampers and fire smoke dampers:

• 1.5 hours (90 minutes) fire resistance
• 3 hours (180 minutes) fire resistance

The fire resistance rating should coincide with the rating of the fire barrier receiving the damper. A three-hour rated fire damper should go with a fire barrier rated for more than three hours.

The ratings are determined through rigorous testing per UL 555 requirements. In the fire endurance test, a sample damper is installed in the opening of a test oven using the manufacturer's instructions.

To pass, the damper must close with its fire response device and hold the closed position for the duration of the test. Temperatures will increase as the simulated fire intensifies. At 1.5 hours, the test chamber will reach up to 1,792 degrees Fahrenheit. For the three-hour test, temperatures will reach up to 1,925 degrees.

Technicians will observe the damper throughout the test to ensure the blades remain intact. If gapping occurs between the blades of a multi-blade damper or large flames pass through to the unexposed side of the damper, then the test ends and the damper fails.

UL Standards for Fire and Smoke

After the fire resistance test, the damper will undergo a water spray test to determine whether it will stay intact and fully closed when firefighters arrive to extinguish the fire. UL 555 requires more tests than we list here before a fire damper can meet fire safety requirements.

Combination fire smoke dampers are rated for fire resistance and smoke leakage. This damper is rated for 1.5 hours of fire resistance and smoke leakage class 1.

Combination fire smoke dampers must complete these tests and the tests laid out for smoke dampers per UL 555S, because they must be prepared for both scenarios. For a full list of tests, and some pointers on installation, check out our free continuing education course on life safety dampers.

The goal of all life safety dampers it to provide time for occupants to evacuate the building. Through compartments and fire barriers, these devices save lives by providing a pathway to safety.

Starting a project and need life safety dampers? Air Balance can help. We build combination fire-smoke dampers for meeting both fire and smoke requirements. Contact us today and let’s get started.

Which is more common in your line of work: 1.5 hour rated dampers, or 3 hour rated dampers? Let us know in the Comments section. We want to hear from you!