- Creato: Lunedì, 12 Novembre 2012 14:41
- Ultima modifica: Giovedì, 17 Ottobre 2019 16:17
- Pubblicato: Lunedì, 12 Novembre 2012 14:41
Ignitability / flammability
There are several small-scale tests able to evaluate materials and components which are victims of the fire in an extensive way.
These tests are described in the IEC series 60695-11-XX, all related to the characterization of the combustion behaviour of a specimen or component in the presence of a flame, therefore suitable for the verification of cases where the product concerned is potentially the victim of fire. Below some of these standards are listed. For example, for the resistance to the combustion of the insulating materials for pre-selection purposes, it is possible to use the following standards:
IEC 60695-11-10 "Fire hazard testing - Part 11-10: Test flames - 50 W horizontal and vertical flame test methods": the standard reports that a specific insulating material can self-extinguish in a given period of time from the beginning of the material combustion. This method also allows to check the propagation speed of the flame vertically and horizontally and allows to check if parts of insulating material can propagate the flame by moving away from the point of combustion (dripping with flame).
IEC 60695-11-20 "Fire hazard testing - Part 11-20: Test flames - 500 W flame test method": this standard is similar to the previous test but with much higher thermal power.
To evaluate the flame behaviour of a component we can instead consider:
IEC 60695-11-5 "Test flames – Needle flame test method - Guide, provision for verification tests and equipment". The test uses the flame generated by a gas flow coming out of a hypodermic needle. we are considering very small powers, however this method is extremely useful to model in real conditions the scenario of a component touched by a small flame, like the one from a connection or any component that is classifiable as the origin of fire.
Finally, there are cases where there is a risk that a product becomes a victim of fire due to overheating and therefore without coming into direct contact with a flame. To characterize these scenarios, it is possible to consult IEC TS 60695-11-11 “Fire hazard testing - Part 11-11: Test flames - Determination of the characteristic heat flux for ignition from a non-contacting flame source”. This test evaluates the behaviour of a material subjected to overheating due to the presence of a flame that does not directly affect it. This is an interesting test to evaluate the behaviour of the insulating materials and / or non-metallic components, when involved with a very high and spatially concentrated heat flow.
- Small-scale tests are often carried out in a controlled atmosphere to ensure the repeatability and reproducibility. However, the ignition behaviour depends on the working temperature and / or the environment in which the product operates in the phases before being in contact with the ignition source.
- It is highly recommended to carry out all the safety assessment tests on the product under standard conditions at zero life time, and possibly supplemented by tests on components that have undergone accelerated conditioning and / or aging that simulates the product state under test, e.g. in accordance with the life time for which it was designed. This is extremely important for the polymeric and / or organic materials present in the component under test, which, by definition, is subjected to the degradation by heat, UV, humidity, and generally in specific environmental conditions.