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DIN Standards Committee Materials Testing

Overview

Fires basically create a hazard to life. In addition to the destructive effect of the combustion, fires are generally accompanied with toxic or corrosive wastewater and natural flue gases. Part 9-1 of the series IEC 60695 in particular discusses influences on the propagation and/or prevention or at least deceleration of flame propagation to surfaces of different materials. The surface spread of flame beyond the area of ignition occurs as a result of the creation of a pyrolysis front on the surface of the material, ahead of the flame front, arising from the heating by the flame and external heat sources. The pyrolysis front is the boundary between pyrolysed material and unpyrolysed material on the surface of the material. Combustible vapours are generated within the region of pyrolysed material, which mix with air and ignite, creating the flame front. The surface spread of flame rate is the distance travelled by the flame front divided by the time required to travel that distance. The surface spread of flame rate depends on the heat supplied externally and/or by the flame of the burning material ahead of the burning zone and on the ease of ignition. The ease of ignition is a function of the minimum ignition temperature, thickness, density, specific heat, and thermal conductivity of the material. The thermal release supplied by the flame depends on the thermal release rate, specimen orientation, air flow rate and air flow direction relative to the surface spread of flame direction. In general, materials show one of the following types of surface spread of flame behavior: a) non-propagation: there is no flame propagation beyond the area of ignition; b) decelerating propagation: flame propagation stops before reaching the end of the surface of the material; c) propagation: flames propagate beyond the area of ignition and eventually affects the entire surface of the material. Properties of the materials that are used to describe the surface spread of flame behavior are associated with surface preheating and pyrolysis, generation of vapours, mixing of the vapours with air, ignition, combustion of the mixture and generation of heat and combustion products. Flame retardants and surface treatments are used to modify the surface spread of flame behavior. Factors that need to be considered for the assessment of the surface spread of flame behavior of materials are: a) the fire scenario (surface orientation, ventilation, ignition source, etcetera); b) measurement techniques (see 5.5) and c) the use and interpretation of results obtained. This safety guidance provides for the assessment of surface spread of flame for electro-technical products and the materials from which they are formed. It provides:- an explanation of the principles of flame spread for liquids and solids, - guidance for the selection of test methods, - guidance on the use and interpretation of test results, and - informative references. It is intended for use by technical committees in the preparation of standards in accordance with the principles and intended measures laid down in IEC Guide 104 and ISO/IEC Guide 51. The responsible body is DKE/K 133 "Prüfverfahren zur Beurteilung der Brandgefahr von elektrotechnischen Produkten und Isolierstoffen" ("Test methods for assessment of fire hazard of electro-technical products and insolating materials") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 133 - Prüfverfahren zur Beurteilung der Brandgefahr von elektrotechnischen Produkten und Isolierstoffen