In some applications, such as electrical panels, the self-extinguishing properties of a product or component assume considerable importance: when the enclosure is located in public premises, such as accommodation facilities or hospitals, or when the electrical panel controls fire systems, or in all those systems where the continued spread of the flame could lead to considerable damages, the degree of flammability of the parts can really make a difference!
Self-extinguishing and plastic materials
Some high-performance plastic materials can be classified as self-extinguishing, flame retardant, non-flammable or intrinsically self-extinguishing plastics, thus making them suitable for preventing the risk of fire.
The plastic material is generally not “fireproof” in the true sense of the word, since, if exposed to direct flame, it still tends to burn. But while many plastics continue to burn when the flame is removed, the self-extinguishing plastics turn off on their own within a short time.
The UL 94 standards of flammability and self-extinguishing plastic materials
There are several standards that make it possible to classify the behavior of plastic materials when subjected to flames. The most common is the flammability test according to UL 94, internationally recognized. It’s divided into six flame classifications, assigned to the materials based on the results obtained on a reduced scale. These classifications are used to distinguish the combustion characteristics of a material after the samples have been exposed to a test flame specified under controlled laboratory conditions.
Next to the acronym UL 94, it is possible to identify 2 values, depending on the type of test performed:
- The HB test, which determines the flammability of a polymer.
- The tests V0, V1, V2, which determine the degree of self-extinguishing of the material
The indication of these classes is found on materials commonly used in production casings, structural parts and insulators of consumer electronic products (UL 94 5VA, 5VB, V0, V1, V2, HB).
Horizontal or vertical positioning
The plastic polymer samples are oriented in a horizontal or vertical position, according to the specifications of the relevant test method and are subjected to a defined flame ignition source for a specified period of time. In some tests, the test flame is applied only once as in the case of the horizontal combustion test (HB), while in other tests the flame is applied at least twice.
Horizontal evaluation HB
The HB (Horizontal Burning) test consists of measuring the time in which the specimen of plastic material of specified thickness horizontally mounted continues to burn after it has been hit by the flame of a Bunsen for 30 seconds.
The material is classified as HB when the 3 mm thick specimen burns at a maximum speed of 76 mm / minute.
Vertical evaluations V0, V1, V2
This test indicates that the material has been positioned vertically and evaluates the propensity of a material to extinguish or spread flames once it’s lit. The tested polymer is evaluated as self-extinguishing if the flame goes out within a specified time, after the ignition source has been removed. The plastic material sample, mounted vertically, is hit by the flame of a Bunsen for 10 seconds, and:
- classified V0 when the flame is extinguished within 10 seconds.
- classified V1 when the flame is extinguished within 30 seconds, without dripping.
- classified V2 when the flame is extinguished within 30 seconds, with dripping.
Therefore, vertical evaluations also indicate whether the test sample dripped inflamed particles which in turn ignited a cotton indicator located below the sample. Furthermore, UL 94 also describes a method in which the test flame is applied for a maximum of five times in the test phase for a 5VA or 5VB type classification.
Difference in methods and test criteria
On the basis of what has just been read, when examining the flame values for commonly printed plastic materials to manufacture casings, structural parts and insulators present in consumer electronic products, a material classified as 5VA or 5VB is therefore subject to an ignition source flame about five times more severe than that used in tests V0, V1, V2 and HB. Furthermore, these types of samples do not drip flaming particles.
Fandis plastic products
Fandis plastic products, such as the Virdis FF series filter units, the Orangis thermostats and hygrostats, use PC/ABS or PBT plastics with UL 94-V0 and UL 94-5VB flammability degree depending on the type of product, guaranteeing then the maximum standards in terms of self-extinguishing and safety.
To learn more about all the Fandis products designed for the safety of the electrical panel, browse our blog, visit our website fandis.it or send an email to support@fandis.it. Our staff will answer you as soon as possible.
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