One of the typical features of all plastics is their poor flame resistance. The demand for self-extinguishing materials is continually increasing due to the necessity to provide higher security levels in the living and working environments and also for technical and mechanical parts.

The fire behaviour of plastic materials can be examined in different ways, according to the standards we wish to take into consideration. Either we only examine the various applied tests or we also consider the possible effects of fire extinguishers or additives whose aim is to retard flame propagation. Generally these additives are compounds based on halogens or phosphorus.
The additives give to the plastic a self-extinguishing power but when burning they emit highly toxic fumes whose opaqueness makes escape very difficult and dangerous. Moreover the fumes emitted are highly corrosive and may damage and/or disable the electronic alarm and aid appliances. Simple "flame resistance" has therefore increasingly lost its importance because of the negative effects of the fumes emitted during burning: density of the exhaled fumes, their toxicity or the oxygen limit.

Experience has demonstrated that in most cases a self-extinguishing plastic material emitting fumes and toxic gases is more dangerous than an unmodified material whose self-extinguishing power is poor but which does not emit dangerous fumes. Different studies on the accidents caused by fire in public places, underground rail systems, etc. has shown that fumes and toxic gases are the prevailing causes of danger for people Moreover, experience has shown that in some fire extinguishers, the polybromides, emit highly toxic and dangerous dioxin and furan. In conclusion, when we have to choose a plastic material, we have to evaluate in addition to the existing laws, the kind of product, its position in the environment, the content of halides or fire extinguisher gases and their effect on the polymer.

FLAMMABILITY according to U.L. 94

The test methods outlined by the American Underwriters Laboratories are the most commonly used to define the flammability of a plastic polymer. It is necessary to specify whe ther the material is modified with a flame extinguisher or if it is halogen-free. The first test HB determines the non-flammability of a polymer. The test V.0 , V.1 , V.2 determines the self-extinguishing grade of a polymer.

UL 94 HB

This test measures the burning time of a horizontally fixed plastic specimen (thickness is specified in the test) after it is brought into contact with the flame of a Bunsen burner for 30 seconds. According to U.L.94 HB (Horizontal Burning) the material is classified H.B: when a 3 mm thick specimen burns at a maximum speed of 76 mm/minute.

UL 94 V.0 , V.1 , V.2

This test measures the burning time of a vertically fixed plastic specimen (thickness is specified in the test) after it is brought into contact with the flame of a Bunsen burner for 10 seconds.

  • according to U.L.94 (Vertical Burning) the material is classified V.0: when the flame extinguishes within 10 seconds
  • according to U.L.94 (Vertical Burning) the material is classified V.1: when the flame extinguishes within 30 seconds without dripping
  • according to U.L.94 (Vertical Burning) the material is classified V.2: when the flame extinguishes within 30 seconds with dripping

SELF-EXTINGUISHING GRADE ACC. TO U.L.94 OF SOME UNMODIFIED POLYMERS

PA6 ( specimen thick. 3 - 6 mm ) = HB - V2
PA66 ( specimen thick. 3 - 6 mm ) = HB - V2
PA66.6 ( specimen thick. 3 - 6 mm ) = HB - V2
PA6G ( specimen thick. 3 - 6 mm ) = HB - V2
PA11 ( specimen thick. 3 - 6 mm ) = V2
PC ( specimen thick. 3 - 6 mm ) = HB - V2
PPOm ( specimen thick. 3 - 6 mm ) = HB
ABS ( specimen thick. 3 - 6 mm ) = HB
PP ( specimen thick. 3 - 6 mm ) = HB
PE 300 ( specimen thick. 3 - 6 mm ) = HB
PE 500 ( specimen thick. 3 - 6 mm ) = HB
PE 1000 ( specimen thick. 3 - 6 mm ) = HB
PVC ( specimen thick. 3 - 6 mm ) = HB
POM c ( specimen thick. 3 - 6 mm ) = HB
POM h ( specimen thick. 3 - 6 mm ) = HB
PET ( specimen thick. 3 - 6 mm ) = HB
PVDF ( specimen thick. 3 - 6 mm ) = V0
PTFE ( specimen thick. 3 - 6 mm ) = V0
PES ( specimen thick. 3 - 6 mm ) = V0
PSU ( specimen thick. 3 - 6 mm ) = HB - V2
PEI ( specimen thick. 3 - 6 mm ) = V0
PPS GF40 ( specimen thick. 3 - 6 mm ) = V0

OXYGEN INDEX

ISO 4589

The test measures the minimum percentage of oxygen in the mixture Oxygen-Hydrogen necessary for the burning of the material.
The highest is the requested percentage of oxygen (LOI value), the lowest is the possibility to burn.

 Tabella indice di ossigeno

The oxygen index ( LOI ) is the lowest oxygen concentration in the presence of which the specimen burns for 3 minutes or for 50 mm.

LOI
PTFE 92
PVDF 43
PI 36
PSU 37
PESU 38
PC 26
PPO.m 31
PA66 25
PET 22
PP 18
PE 18
POM 16
According to the standard ASTM D 1929, this is the temperature at which the ignition and auto-ignition in air of a specific quantity of plastic material occurs. Many other standards test the fire resistance of the material on a different basis, according to their specified requirements. ignition - autoignition temp.
PESU 550 - 550
PEI 520 - 530
PA66 500 - 520
PA6 450 - 480
PTFE 530
PVDF 430 - 480
PET 370
PE 350 - 350
POM 330 - 380

Further tests

Other tests, such as: EVALUATION OF SMOKE DENSITY according to standard ASTM E662, EVALUATION OF TOXICITY OF THE FUMES CEI 20-37; are used for the approval of plastics in the fields: aeronautics, shipbuilding, railways, etc. Omnia Plastica and its technical staff are at your disposal for further advice.