Horizontal Burning Test

Introduction

The horizontal burning test is a basic technique of testing the flammability of plastic substances, particularly when applied to electrical appliances, car components, and consumer goods. Catalogued as a horizontal flame test (like UL 94 HB), this test method establishes the rate of burning of a material exposed to a small-sized ignition source. The information is a necessity in formulating the fire performance of the materials and aligning them with safety controls. This test is relatively simple to conduct, repeatable, and pertinent, making it one of the most common tests of materials.

Instrumentation

The horizontal burning test arrangement requires a test chamber or enclosure to eliminate the effects of air drafts and a precise butane or methane gas burner to enable flame ignition, a sample holder that keeps the specimen in a horizontal position, and a timing device to record the burning time. The ruler or measuring scale helps ascertain the distance covered by the flame. There are also markers in the test equipment used to determine the measuring points along the portion of the sample. In the case of standardized testing, the whole arrangement needs to fall within the specifications provided in UL 94 or other standards of testing.

Principle and Methodology

The horizontal burning test involves conditioning a piece of this material and then inserting it horizontally into a sample holder. The free end is brought into contact with a flame for a specific time of about 30 seconds. Once the flame is removed, the level of time taken by the material to burn to any two marks, which are predetermined, is noted. The linear burning rate is determined by dividing the distance that has been burned by time. A material is HB when the sample that is less than 3 mm in thickness burns at or below 76 mm/min or when it extinguishes itself before the second mark is reached. The technique provides a sure screening endeavor in the assessment of the rate at which a material will undergo combustion on burning in a horizontal position.

Strengths  

Among the principal advantages of the horizontal burning test are ease of use and the fact that it is not expensive. It utilizes minimal equipment and is useful in giving comparative data as regards material flammability. The test proves especially useful when a preliminary window of potential plastics or polymers is sought in an application in which flame spread needs minimization. 

Limitations

The test, however, is limited, especially by the fact that it fails to provide comprehensive coverage of vertical or real-life burning events. It makes no consideration of so many things, like dripping or the rate of heat release, as well as by-products of combustion. Moreover, results can be affected by some elements of the environment (e.g., humidity or sample conditioning).

Importance

The horizontal burning test is a critical part of fire safety engineering and material testing. It assists in creating flame-retardant products and aids manufacturers in meeting the laws that regulate flammability on consumer electronics, cars, and household appliances. It is a useful screening device for selecting materials and controlling quality.