Limiting Oxygen Index as per ISO 4589

The purpose of testing the limiting oxygen Index (LOI) is to measure the relative flammability of a material during flame impingement in a controlled environment. The LOI states the minimum concentration which is required to maintain a flame impingement of the thermoplastic material for 3 minutes or for a length of 50mm. The atmosphere in the testing cylinder consists of a N2/O2 composite which is controlled from the outside. The vertical supported sample is set alight with a pilot flame from above. The pilot flame is removed and the oxygen concentration is reduced until the test piece cannot feed the flame anymore. The higher the LOI is, the lower the flammability of a material is.

Pciture 8:

Limiting Oxygen Index as per ISO 4589

Chart 22: Limiting oxygen index

Lexan Valox Ultem


In comparison to other polymers, the GE-films characterise through their high flame resistance. Because of that they are used for numerous applications in the electro-technics and electronic, in the automotive construction and in the building industry. GE-films with flame retardancy offer increased resistance against flame impingement.

Reaction to fire according to UL94 – preliminary remark

Standard 94 of the Underwriters Laboratories (UL) established itself worldwide as the most important norm for the classification of the flammability of plastics. According to UL94 the property of a material to turn off on laboratory conditions after inflaming, is tested. The classification depends on the burning rate, the time it needs to go out, drop- (aflame/non-flame) or hole formation and the duration of afterglowing. There are several possible classifications for every material, it depends on the wall thickness and/or colour. When selecting the concrete material, it should always made sure that the classification which is equal to the thinnest wall-cross-selection, is taken. Information about the UL94 classification is only comparable and meaningful if the relevant wall thickness is stated.

An overview for the UL-94 classification*

HB-test piece horizontal, burning rate <76 mm/min for wall thicknesses under 3 mm or under 38 mm/min for wall thicknesses of more than 3 mm.

V-0- test piece vertical, self-extinguishing up to 10 s, no burning drops, afterglowing of max. 30 s

V-1- test piece vertical, self-extinguishing up to 30 s, no burning drops, afterglowing of max. 60 s

V-2- test piece vertical, self-extinguishing up to 30 s after removing the flame, burning drops acceptable, afterglowing of max. 60 s

5V- bigger flame, test piece vertical, self-extinguishing up to 60 s after 5 x 5 s
flame impingement, no burning drops, afterglowing of max. 60 s

5VA- like 5VB, but no burning holes accepted – highest UL94-classification at the moment

5VB- like 5V, but the plate-shaped testing piece is horizontal, burning holes accepted after turning off

VTM-0- classification for very thin materials, requirements like V-0, test piece is not rod-shaped but cylindrical


Usually the usage of materials certified to UL94 HB is permitted whenever flame resistance is required because of fire prevention. HB materials also are not recommended for electrotechical applications except they are only used for mechanical and/or decorative purposes. Suitable HB materials are also available for connector casings which require a high comparative tracking index. Frequently misunderstood: materials without fire protection or such which are not suitable for FR applications do not fulfil the HB criterions automatically. Although HB is the lowest flammability classification according to UL94 it can only be met after testing.

Picture 9: Testing for materials with wall thicknesses of up to 3mm according to UL94 HB

Testing for materials with wall thicknesses of up to 3mm according to UL94 HB

UL94 V-0, V-1 und V-2

Test rods with same measurements like they are for the HB test are tested with a flame which is as high as it is for the HB test but for this classification the test rods are hold vertically. Essential is the burning- and glowing time as well as if there are burning drops and if these light the test setup cotton which is only acceptable for V-2. Burning drops are said to be the chief cause for flame propagation in case of fire.

Picture 10: Testing according to UL94 V-0, V-1 and V-2

Prüfverfahren UL94

*Depending on the film model and –thickness; GE films are available for all mentioned criteria. Classifications according to this norm cannot be seen as a hazard index for the tested materials or other materials in case of fire.

**Please contact our laboratory and application engineering for more information.