What is a leakage class and how is it determined? Take a closer look at how smoke dampers receive a leakage class with this quick Condenser article.
There are two leakage classes for dampers. There is the leakage class for air leakage, tested under AMCA 500-D, and a classification for smoke leakage. Smoke leakage is tested under the UL standard for smoke dampers, UL 555S.
UL 555S consists of several tests that determine whether a damper will function as a smoke damper. Read our article on smoke dampers for the full breakdown of these tests. These tests are rigorous. Each test is conducted one after the other, under conditions like a fire event. Leakage testing is one of several tests conducted in this sequence.
The leakage test is conducted at the end of the ambient operations test. Three dampers of the same model must close three times against a minimum airflow rate at ambient temperatures. The three dampers are different sizes of the same model:
On the third closure, testers measure the amount of leakage passing through the closed dampers. Once measured, the damper is reversed in the test assembly and the tests are repeated. Upon completion, the damper is reinstalled in its original position and the tests are conducted against a heated airstream.
Testers compare the leakage of the first two dampers against the maximum-sized damper, across all iterations of the test, to come up with a leakage class.
The leakage class can be class I, class II, or class III, depending on the amount of leakage measured during the tests. Class I smoke dampers have the least leakage:
This is considered the best leakage class because it allows for the least amount of smoke leakage. To compare, class II smoke dampers allow for 20 cfm per square foot at 4.5 in. w.g and class III allows for 80 cfm per square foot. For smoke dampers, class I leakage is the best option.
Smoke dampers must close quickly and tightly the moment smoke is detected in the airstream. Although it isn’t an airtight seal, the smoke damper slows the spread of smoke through the rest of the duct. Leakage tests, and other smoke damper tests, ensure that each damper is prepared to respond during an emergency.
For more on life safety dampers:
Looking to meet life safety requirements? Contact Air Balance about our fire smoke dampers, rated for fire resistance and smoke leakage. Let's work together to meet your project's requirements.