Fire classification of cables (part 1)
Fire safety is regulated by law, and supervision of the accurateness of the regulations, their observation and risk assessment is ensured by fire experts. However, no valid fire classification of cables has been made until recently. The European Commission undertook to fulfil this important task.
Fire classification of cables is a real breakthrough from the perspective of designers, contractors and companies which plan building investments – regardless of the type of such an investment (office, hotel, hospital, public facility, industrial building, etc.).
A fire in buildings and its impact
Life and health are fundamental values to protect. Safety of people during a fire in a building is of the greatest importance.
About one third of fire incidents occur indoor. Evacuated persons often have only a few minutes to safely escape the building before the spreading smoke limits their orientation capabilities, making it difficult to find evacuation routes. Persons leaving an affected area must get through a dense cloud of toxic fumes which limit the sight range.
Fire growth modelling in buildings
A fire is usually triggered by the combustion of local ignition sources which further ignite surrounding materials. At this stage, the temperature rises until (>300°C). Thereby, plastics in the room are ignited due to a chain reaction at about 450°C. The released heat sets nearby furniture and equipment on fire. During the ignition and fire growth phase, the temperature continually increases and huge amounts of burning pyrolysis gases, which constitute mixtures of gases such as hydrogen, methane or carbon oxide, and organic components are released. At a certain stage, air which infiltrates the room causes ignition of pyrolysis gases under the ceiling which is called flashover. High temperatures make all flammable materials immediately burn without a contact with any flame. The last phase is at temperatures above 1000°C, where burning is maintained. It is a stage at which all flammable materials burn and there is no energy that could be released.
In a report of the Swedish Rescue Services Agency (SRSA) on the prevention of fire, there is a following fragment: it may only take a few seconds from the ignition of a fire to its flashover. Today, already after three minutes extremely hazardous conditions may occur. With the increase of the quantity of plastics in buildings, in recent years the time between ignition and flashover becomes shorter and shorter.
Cables under fire conditions
In the event of a fire, cables can facilitate the start of a fire and its propagation to the surrounding rooms. According to the statistics of the German Institute for Damage Prevention and Research (IFS), about 33% of all fire examined can be attributed to the electric power. This percentage increased within the last years according to the fire cause statistics. Defective devices, aged connectors, an improper electrical or connection system quickly lead to smouldering fire. Such a fire is often discovered very late. Smouldering fire may lead to the release of toxic substances.
Cables can spread fire from one room to another, leading to fire propagation.
Low fire-hazard cables improve safety
Cables usually consist of a metallic (or optical fibre) conductor, organic insulation and sheathing materials. Such organic materials vary in their flammability and emitted smoke density.
Cables may contribute to fire propagation due to their arrangement in buildings, therefore this hazard has been considered in multiple national regulations and recommendations for many years. Use of self-extinguishing or fire-retardant materials in cable components may affect their reaction to fire. In such systems it is particularly important to use fire-retardant materials which may reduce fire propagation. Smoke density and acidity of released gases constitute parameters and crucial criteria for selection of materials which limit the emission of toxic gases during a fire. Limiting these gases and opaque smoke to an absolute minimum is of great significance. These criteria are fulfilled by fire-retardant halogen-free cables.
It is crucial to reduce the exposure time of people to hazardous gases by ensuring smooth and safe evacuation with the best visibility possible.
Longer escape times are essential
The University of Lund in Sweden conducted a study using computer programs designed for simulating the propagation of smoke and gases released during combustion in buildings and people’s behaviour in the event of a fire alarm. Different types of cables were tested. The results showed that with conventional cabling only persons evacuated within 53 seconds were able to leave the building on time. This shows how important fire retardation is. On the basis of the flammable product measurement results according to the fire scenario as per EN 50399, a study was conducted to determine the behaviour of cables under simulated extreme evacuation conditions. The examinations confirmed that low fire-hazard cables can substantially reduce the general risk in the event of a fire. By using materials with a low level of opacity smoke produced, visibility and chances to escape were significantly improved.
Cables as construction products - considering fire safety of construction products
Fire safety is usually ascribed to structural elements or construction materials – other construction products were usually not focused on. Since the Düsseldorf airport fire in 1996, it became apparent that fire safety issues concern also other product groups. With the Construction Products Regulation (CPR), which came into force in July 2013 and is mandatory for all European Union member states, the EU created a clear legal framework for properties of such products. According to the above regulation, ‘a construction product means any product or kit produced and placed on market for incorporation in buildings or their parts in a permanent manner and the performance of which has an effect on the performance of buildings with respect to the basic requirements for buildings’. According to this definition, cables are construction products if manufactured for incorporation in buildings in a permanent manner. The term ‘permanent’ means that the system is intended not to be temporary.
Consequently, cables which are incorporated in buildings comply with the definition – even if plastered or laid in technical shafts. The regulation also refers to electric cables installed a permanent manner in order to supply a building with electric power (single cables and cable bundles). The regulations do not concern cables designed for connection of devices to a building through a connector. These include but are not limited to power cords connecting appliances, e.g. lamps or machines, with the power grid. Permanently fixed transmission cables meet the regulation requirements. These which are not installed in a permanent manner (e.g. in Data Centers) and are detachable, e.g. crossover cables, do not comply with the definition.
Accordingly, cables which are permanently incorporated in a building and for which harmonised standards on the basis of the Construction Products Regulation exist (power, control and communication cables) are subject to fire protection regulations. New fire protection categories for cables established in Europe require a reassessment of fire safety in buildings.
The second section describes specific propositions for the division of Euro classes and their range of application.
Drawn up by
Michał Piechulek, MSc
Director of the Katowice Department
This article contains information included in the ‘Low fire-hazard cables improve safety’ document published on 15 September 2015 by ZVEI – Zentralverband Elektrotechnik- und Elektronikindustrie e.V. (http://www.zvei.org/Publikationen/Low-fire-hazard-cables-improve-safety-..., as of 19.07.2016).
The article was originally published in the ‘Zabezpieczenia’ journal, no. 4/2016.
