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Material Characteristics
A brief discussion of material characteristics for the three different alternative sheathing materials used for PVC, halogen free and plenum cables. PVC materials PVC materials have generally fine and stable mechanical performance. Fire propagation behavior may be fine, but smoke and acid generation during fire are main problems which must be considered in certain fire scenario. Environmental legislation will limit some types of compounds in certain countries. PVC sheathings are significantly affecting temperature performance of attenuation, but only for unscreened cables. In most cases the degradation is well within the specified limit. However, this should always be verified, also in cases where the PVC compound is "just" changed in connection with regular production. Halogen free materials Halogen free materials are frequently based on EVA (ethylene vinylacetate copolymer), but also flame retardant PE (polyethylene) is applied. EVA compounds are containing magnesium or aluminium hydroxydes to facilitate flame or fire retardancy. These hydroxides are forming water when heated and thus creating flame or fire resistance. EVA based materials may be applied in both flame and fire retardant cables. PE based materials are, as far as 3P knows, only applied in flame retardant cables. Halogen free materials have improved significantly over the past many years, but still a general problem for the EVA based materials is the mechanical behavior. The elongation of the sheath is usually close, but safely over the specified limit (min. 125 % elongation at break). However, if production is not well controlled it may be reduced significantly. 3P estimates that performance is only affected in the very few cases where a very low elongation is found. Plenum type materials Plenum type materials are usually based on fluorocarbon (FEP) compounds, with or without mixing with other materials. Plenum type cables are commonly used in the US, while Europe has so far alternatively focused mainly on halogen free cables. PVC type cables are applied everywhere. Plenum materials are having superior fire propagation resistance, but lower smoke and acidity performance than halogen free materials. Depending on the focus one could therefore rate the better fire propagation of plenum cables or the lower smoke and corrosivity of the halogen free cables for most valuable. The costs of the plenum cables are significantly higher than the costs of the halogen free cables. This point must of course also be included in any decision making concerning application of plenum type cables. Safety of Cables
Safety of cables is a key issue for producers and users of cabling, both with respect to personal safety and to equipment protection (corrosion) in case of fire. Presently the safety issue only concerns cables, but in the future 3P believes that also connecting hardware will be the target of the safety regulations. Until recently most cables for LAN installations were PVC sheathed, and halogen free cables were only applied in a few special cases. However, a significant change of attitude and regulation is now developing in the market, for instance in CENELEC standards EN 50167, EN 50168 and EN 50169 by direct specification that screened cables must be halogen free. These new requirements to halogen free cables have impact on the safety and especially the fire rating of the cables, as discussed in the present 3P Newsletter. Arguments for turning to Halogen Free Cables
PVC is in most respects an ideal sheath material. Superior mechanical characteristics are combined with high reliability. However, two main drawbacks have forced the development of alternative, halogen free sheath materials. The second disadvantage forcing substitution of PVC concerns the fire behavior. In a fire situation burning or extensive heat causes: Development of a heavy black smoke
Development of hydrochloric acid and some poisenous gasses. Benefits and Drawbacks of Halogen Free Sheath Materials
For the above reasons the search for an alternative to PVC has been intensive and proved to be successful. A number of compounds are available today, mainly based on the plastic material "EVA" filled with aluminium or magnesium hydroxyde. Fire retardancy comes from generation of water during fire. Fire and Flame Retardancy of Halogen Free Cables
A benefit for the halogen free cables is a better fire performance than possible for PVC cables. Unfortunately a large number of fire and flame tests exist and it is therefore not always clear which fire or flame performance a specific cable offers. Flame retardancy according to IEC 332-1 (Corresponds to HD 405.1) is verified by burning one cable with a single flame. IEC 332-1 is and will be the fundamental flamability rating for all cable types, including also PVC sheathed cables. All international communication cables must pass this requirement. Fire Retardancy according to IEC 332-3, Cat. C (corresponding to HD 405.3) is verified by burning a bunch of cables with a large burner. IEC 332-3, Cat. C is the additional flammability rating that presently is mandatory for halogen free screened cables. However, the position with respect to the IEC 332-3, Cat. C requirements is both clear and confused: Clear requirement: If you install screened cables and need compliance to EN 50173 (and therefore EN 50167, EN 50168 or EN 50169) you must install fire retardant, halogen free cables. Confusion: No formal fire retardancy requirement exists for unscreened cable. Not because of international disagreement that unscreened cables should also be fire retardant and halogen free, but simply because standardization of unscreened cables is missing due to open EMC discussions. Furthermore the fire retardancy requirements of screened cables might be reconsidered in the future updates of the standards. The valid argument is being discussed: Why should the halogen free cables be forced to have added costs in order to pass fire retardancy requirements (because of thicker sheath needed), when PVC sheathed cables have never passed this requirement?
Flame and Fire Retardancy according to, or covered by American Ratings like CM, CMX, CMR and UL VW-1
Identification of Halogen Free Cables
All cable designations are describing the same cable type, except for "FR" since halogen free cables may be either fire or flame retardant. Environmental Considerations
Environmental considerations for PVC are only indirectly a concern for the end user. Environmental considerations for PVC are only indirectly a concern for the end user as legislation will be regulating any limitations for compounds or use. An example is ban of certain constituents formerly generally applied in PVC compounds, like the heavy metals cadmium and lead. Use of PVC sheathed cables must of course be in compliance with the national or international regulations of the country in question. Other discussion points related to the general environmental behavior of PVC are often found in the public debate. Key words like "acid rain", "dioxine formation", "pollution with heavy metals", "fertility of man and male animal" and "cancer risk" are popular environmental arguments against PVC. If and how these issues may affect the future application of PVC cables cannot be concluded by 3P. Fire Safety Considerations
When considering the different cable safety options (PVC, LS0H and LSFR0H) one should focus on both equipment safety and human safety in case of fire. Equipment safety Equipment safety is critical in case of a small fire where PVC is burning. In case of a major fire all equipment will of course be destroyed by the heat, but very often a fire is limited heat-wise and then PVC may cause extremely expensive secondary fire expenses (multimillion Euro secondary fire damage is known for even marginal fires). Example: In a corner of a factory a small fire includes PVC materials. Insignificant heat damage is limited to the burning corner, but the smoke had penetrates all the building and hydrochloric acid condenses on all cold surfaces (i.e. actually most critical far from the heat of the fire !) destroying electronic equipment and steel structures in the wall due to corrosion. Immediate cleaning will in this case significantly limit damages, but may of course also be costly depending on damage level. The consequence of the the above considerations is that PVC cables or other PVC containing components should not be applied where critical or expensive electronic equipment may be exposed to the smoke in case of fire. Human safety Human safety is affected when PVC is burning due to development of a heavy black smoke, hydrochloric acid and some poisenous gasses (poisenous gasses are always developed by any fire, especially carbonmonoxide). Together these two factors affect human safety in case of fire. The smoke causes panic as escape routes cannot be seen. The poisenous gasses causes asphyxiation if people cannot escape the smoke in a short time. It should be realised that other materials are also causing the same negative effects in case of fire. Concern about other materials must therefore also always be included to improve human safety in case of fire. The consequence of the the above considerations is that PVC cables or other PVC containing components should not be applied where many people are assembled and have difficult escape routes. Construction Products Directive (CPD)
In Europe much attention has for the past many years been focused on developing statutory cable fire safety requirements under the Construction Products Directive (CPD-requirements). The significance of the CPD for cables will be critical in Europe. Requirements to fire safety will be statutory as they will not "just" be determined by standards, but by European law. Costs of cables will then in the future be conditioned by the specified fire safety regulation applicable for a certain installation. So far no final agreement has been made, and presently the decision has been delayed for a minimum of an additional 4 months (at least to October 2005) with no certain positive outcome this year. General Advance Information The following general advance information about the CPD can be provided: The CPD for cables, as presently drafted, contains 6 different EuroClasses of safety ranging from Aca (no burning) to Fca (no limitation of burning). EuroClass B has been split into two sub-classes B1ca and B2ca satisfying either "plenum type" or "LSFR0H type" requirements. Sub-ratings are applied for some EuroClasses in addition to the fundamental fire ratings. This involves smoke generation, acidity of smoke and formation of burning droplets. Passing of the CPD requirements for cables will be documented by CE marking of the cables, but is of course only possible after its agreement. After agreement of the CPD for cables it will be determined by each individual European country how the market implementation will be. As an imaginary example a country might decide that all hospitals will be EuroClass Cca and then all cables installed in hospitals in this country must be minimum EuroClass Cca. Cable Testing 3P now has a facility for carrying out the CPD testing of cables. Testing of both flame retardancy, fire retardancy, smoke density, acidity of smoke and CPD fire testing are covered by the 3P certification activities. 3P Fire Safety Testing
Fire safety testing is carried out for the three different cable types: PVC, LSOH and LSFROH. The three versions of a specific cable are listed independently in the 3P survey of qualified cables. A qualification of one of these cable types (for instance the cable version with PVC sheath) does not automatically lead to qualification of one of the other types (for instance the similar cable in LS0H version), since the sheathing material may critically affect both mechanical and electrical performance. Evaluation of performance for each sheathing type is always required. The following fire safety testing is carried out for the three different cable types:
A cable with PVC sheath is verified for:
A cable in LS0H version is verified for:
A cable in LSFR0H version is verified for: 3P Fire Safety Ratings
Halogen free cables are identified by two 3P ratings Halogen free cables are identified by the following two 3P ratings:
Other Names Unfortunately, no internationally recognized names exist for the two cable types. Some other commonly applied names for LS0H are:
LSZH (Low Smoke Zero Halogen) Other commonly applied names for LSFR0H are:
LSFRZH (Low Smoke Fire Retardant Zero Halogen) Significance
Fire behavior of cables has major significance for end users. Fire safety of cables concern both human safety and equipment damages in case of fire. Cables form of course only a small part of a building, but also an essential part. Cables may be located in areas and spaces with ventilation or along ceilings, where fire propagation is especially agressive. Furthermore, they may be placed in areas where they are the main burnable building part, or is the potential cause of extreme burning damages. Consequently fire behavior of cables has major significance for end users. In the past cables were mainly PVC sheathed as this material offers splendid mechanical and climatic performance. The disadvantage in case of fire is unfortunately development of dense, black, suffocating and highly corrosive smoke. Therefore, the application of alternatives were developed and has got increasing popularity. Most popular of these alternatives is halogen free compounds based on "EVA", but other materials are also used. These PVC alternative cables are commonly identified as "halogen free". The the main constituent of PVC is chlorine, which is in chemical terms a "halogen" (like fluorine and bromine, which are also commonly used in electronics for building up fire retardancy). All materials have their special characteristics as discussed elsewhere. |
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