There are many different national and international regulations that apply to the ignition and burning behaviour of thermoplastics. Some of the most important are explained briefly here. For each market and region, specific legislation should be checked.

UL 94 Flammability testing
Underwriters Laboratories UL 94 ratings are the most widely accepted standards for flammability performance of thermoplastics. They are intended to determine a material’s ability to extinguish a flame. Materials are classified based on rate of burning, time to extinguish, ability to resist dripping and whether or not drips are burning. The main tests for this classification are UL 94 HB, UL 94 V2/V1/V0 and UL 94 5 VB, listed in order of severity of the test. The rating of a material is affected by its colour and the thickness of the test bar. Therefore the UL rating should apply to the thinnest wall section in the actual plastic part.

For our UL Listings, look at the following page: http://www.nilit.com/plastics/certifications_ul-listings.asp

UL 94 Hot Wire Ignition testing
The purpose of this test is to determine the materials ability to resist ignition when it comes into contact with glowing elements, like overheated electrical wires or contacts. For this test, a copper wire is wrapped around a sample, and heated up 930 °C. The time it takes to ignite a sample is recorded. UL divides up the HWI ratings into the following performance categories:
 
Ignition time                   UL PLC number
Less than 7 seconds                       5
7 to 15 seconds                              4
15 to 30 seconds                            3
30 to 60 seconds                            2
60 to 120 seconds                          1
Over 120 seconds                           0

 

HWI Listings for various grades:


 
IEC 695-1-1 Glowwire test
The purpose of the glow wire test is asses the fire risk when a component in the vicinity of thermoplastic parts overheat. A glow wire with a defined temperature is brought into contact with the thermoplastic for 30 seconds three successive times. Two different temperature are defined:
GWIT:
The highest temperature where there is no ignition of the plate after 3 successive contacts with the glow wire, with 25 °C added on to the temperature. The value is dependend on the wall thickness, so the temperature is always accompanied by a wall thickness.
GWFI
The highest temperature at which the flame extinguishes within 30 seconds after each of the 3 applications. This value is also depends on the wall thickness.

The following Nilamid grades have a UL yellow card listing:

Limiting Oxygen Index
The limiting oxygen index is defined as the minimum concentration of oxygen in the atmosphere, expressed as a percentage by volume, which can sustain flame on a thermoplastic material. The test is carried out in an externally controlled atmosphere of nitrogen and oxygen. Materials with LOI values over 21% will not burn under atmospheric conditions.

The LOI value of PA66 in it’s natural form is 28%; flame retardant grades have values of up to 35% LOI.