CEI - Comitato Elettrotecnico Italiano

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Can the potential thermal ignition conditions be characterized?

Does the product cause ignition?

A dangerous product can ignite and, in this case, is defined as the fire origin. In the flame absence and under normal operating conditions due to malfunctions or wear problems, the product can generate a flame because of phenomena such as arcs electric surface or air, or overheating, creating the conditions that can lead to a large-scale fire.

Consequently, all the components and the electrotechnical products supporting or containing electrical contacts are potentially fire sources.

A product that is the cause of the ignition has to be surely evaluated in each part that can be individually identified as the fire origin (e.g. each connection point inside a complex equipment).

The assessment has to check the easy to ignition, the combustion behaviour (the combustion and the flame out times, the heat release, the smoke emission in quantity and quality) and finally the propagation speed which is a key factor for determining the fire hazard in a given scenario.

Starting from the tests on a small scale, find a complete application in the standards design phase simulating, in the absence of flame, the malfunction of components with electrical connections that are part of more complex equipment and of the polymeric insulating materials of which the components are made (e.g. materials providing support and / or housing of the connection). These tests are listed in IEC 60695-1-21.

The tests are based on the simulation of an overheating generated by an electrical connection with an incandescent wire, are described in the following standards:

IEC 60695-2-10 “Fire hazard testing - Part 2-10: Glowing/hot-wire based test methods - Glow-wire apparatus and common test procedure”: this standard defines the glow wire equipment and some instructions common to all the tests related to the use of the relevant equipment.

IEC 60695-2-13 "Test methods with incandescent wire. Methods of proof of the reliability of materials": this standard defines the criteria for conducting and evaluating the test on a standard plate of the insulating material of which the component concerned is made. This method evaluates whether the mass of the material under certain overheating conditions of the connection can ignite, generating a combustion of more than 5 s. This is a minimum condition necessary to consider the material ignition and the possible fire propagation. If the flame does not appear or is less than 5 s, a temperature of 25 °C higher than the test temperature is assigned as the temperature at which the material ignites. In the event of a flame exceeding 5 s, the following method can show the combustion characteristic. The glow-wire method can be used as a pre-selection test with a pass / fail evaluation if the test temperature is already defined by the product standard.

IEC 60695-2-12 “Fire hazard testing - Part 2-12: Glowing/hot-wire based test methods - Glow-wire flammability index (GWFI) test method for materials”: this standard defines the criteria for conducting and evaluating the test on a standard plate of insulating material of which the component concerned is made. This method evaluates whether the material in certain overheating conditions of the connection, once turned on, is able to switch off in a defined time; i.e. the material does not switch off because of the total consumption of the material itself (fuel). It is subsequently applied to the test in IEC 60695-2-13 to completely characterize the material behaviour, either as an easy to ignition and to stop the flame under certain temperature conditions. The test method can be used as a pre-selection test with a pass / fail evaluation if the test temperature is already defined by the product standard.

IEC 60695-2 -11 “Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods – Glow-wire flammability test method for end-products (GWEPT)”: the standard defines the criteria for conducting and evaluating the test of the component to decide if the component can become the fire origin (it ignites) and, in this case, how it behaves during the combustion. In practice, the evaluation criteria applied are taken from the two previous methods.

Caution:

1. 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 element.

2. 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.