Sealing Shielding

Environmental Seal Enclosures: UL94 V-0

LED light, flood light, seal enclosureMaterial certifications play a vital role in determining whether a chosen seal material is suitable for your service. In a continuation of our series on environmental seals for enclosures, we will be discussing a specific certification, UL94 V-0. Parker Engineered Materials Group has found that UL94 V-0 certified material is crucial for customers operating in the Renewable Energy, Telecommunications, Power Generation, Chemical Processing, and General Industrial markets due to interest for flame retardant materials. These customers want to ensure their connectors, instrumentation, or equipment enclosures are capable of withstanding a certain degree of fire exposure without compromising the integrity of their assembly. I will go into detail about what the UL94 V-0 certification is, how the test is conducted, and what Parker materials are available with this certification. 

UL94 V-0

Underwriters Laboratories (UL) standard 94 outlines test methods intended to measure the flammability properties of polymeric materials in response to small open flame or radiant heat sources in a controlled laboratory condition. UL94 is performed on the individual components giving the end-user a high degree of confidence that fire testing will be successful on the final product. 

Test methods

The UL 94 standard has methods for both a horizontal (HB) and vertical (V) burn test. Of the two, the vertical burn test can be the most destructive, as it provides the highest degree of flame and material interaction. The diagram below shows a comparison between how the UL94 HB and UL 94 V are tested. 


UL94 HB – Horizontal Burning Test    UL94 HB – Horizontal Burning Test 


Within the vertical burn test there are several classifications that you will see: UL 94 V-0, UL94 V-1, and UL94 V-2. Each classification calls for a specific degree of exposure and guidelines (refer to the chart below) for how long an after flame or afterglow may be present when the flame is removed. An after flame occurs because even though the fire was removed, the remaining material is still combusting. For instance, if we look at the UL94 V-2 classification in the chart below, we see that an initial flame is exposed to the material for 10 seconds. After the burner is removed, the flame may be present on the material for up to 30 seconds. The material is then subjected to a second application of the burner and after removal the material may continue burning for up to 60 seconds. During the burner process, a cotton indicator is located below the material and flame to catch any flaming drops of material. Under UL94 V-2 the cotton indicator is allowed to catch fire, while under UL94 V-1 and V-0 the indicator must not ignite. The flame application process is continued for five samples and the total after flame is measured and must meet the requirement of 250 second maximum for V-2 rating. As the rating moves from V-2 to V-0 you can see that the requirements become more stringent and the total time of after flame decreases dramatically. 

UL Chart

Materials offered by Parker

Parker Engineered Materials Group has found that the stringent requirements of the UL94 V-0 material certification provide the safest and most reliable solution for customers with fire safety concerns. We have developed our silicone material, S7395 to meet the UL94 V-0 requirements. S7395 is also resistant to fungal grown per ASTM G21-96 and is available in a wide variety of shapes and cross-sections to allow for custom configurations in many types of applications.

Be sure to keep on the lookout for our next follow up blog on enclosures and environmental sealing. For more information on additional products visit the Parker O-Ring Division Website.



Michael Sobeski


This article was contributed by Michael Sobeski, Product Engineer, O-Ring Division.







Related content:

Environmental Seal Enclosure 101

Sealing for Harsh Environmental Conditions in Telecommunications Applications

Sealing Groove-less Applications with Flat Panel Gaskets

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Comments for Environmental Seal Enclosures: UL94 V-0

It's very useful. UL 94 testing(TF328), a common test in the flammability testing labs, which is used to test UL flammability rating of plastics. The UL94 test chamber has two test modes, which respectively are horizontal flammability test and vertical flammability test.

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