BSI British Standards

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1 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW raising standards worldwide BSI British Standards Telecommunications equipment and telecommunications cabling Code of practice for fire performance and protection

2 Publishing and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2009 ISBN ICS ; The following BSI references relate to the work on this standard: Committee reference TCT/7 Draft for comment 09/ DC Publication history First published November 2009 Amendments issued since publication Date Text affected

3 Contents Foreword ii Introduction 1 1 Scope 2 2 Normative references 3 3 Terms, definitions and abbreviations Terms and definitions Abbreviations 4 4 Balanced approach to fire threat mitigation General Compartmentation within premises Management of fire threats associated with telecommunications cabling infrastructure Additional measures based on installation type 10 5 Fire protection measures Containment Detection systems Suppression systems 13 6 Fire threat mitigation by cabling component selection General Ignition and flame spread Impact: Heat release Impact: Fire effluent 18 Annexes Annex A (informative) Consideration of fire hazard 22 Bibliography 25 List of figures Figure 1 Examples of pathways in different types of premises 2 Figure A.1 Relationship of the processes involved in the ignition, flame spread and impact of fire 22 List of tables Table 1 Ranking of fire threats 6 Table 2 Mitigation of fire threat 15 Summary of pages This document comprises a front cover, an inside front cover, pages i to ii, pages 1 to 26, an inside back cover and a back cover. BSI 2009 i

4 ii BSI 2009 Foreword Publishing information This British Standard is published by BSI and came into effect on 30 November It was prepared by Technical Committee TCT/7, Telecommunications Installation requirements. A list of organizations represented on this committee can be obtained on request to its secretary. Relationship with other publications The recommendations of this British Standard are intended to support the requirements specified in BS 6701 relating to the installation, operation and maintenance of telecommunications equipment and telecommunications cabling. Use of this document As a code of practice, this British Standard takes the form of guidance and recommendations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading. Any user claiming compliance with this British Standard is expected to be able to justify any course of action that deviates from its recommendations. Presentational conventions The provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is should. Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element. Contractual and legal considerations This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations.

5 Introduction Telecommunications cabling infrastructure includes: telecommunications cabling, comprising cables, cords and connecting hardware intended to support the operation of information technology equipment as, or as part of, a telecommunications system; closures housing connecting hardware; cable management systems housing cables and closures; cabinets, frames or racks within which closures may be installed. The telecommunications equipment connected to the cabling generally requires a power supply, often provided by mains power cabling. With a few notable exceptions, all materials within the telecommunications cabling infrastructure, equipment and associated mains power cabling are flammable. When subject to fire conditions, telecommunications cabling presents a specific potential threat because: there are specific areas in which the concentration of cabling is very high (such as equipment rooms and telecommunication rooms [see the generic cabling standards in the BS EN series]) resulting in increased impact of fire in those areas; telecommunications cabling is widely distributed throughout buildings within pathways, which create routes for flame spread between areas within the buildings. The types of pathway within which the cable management systems are installed are, to some extent, influenced by the types of premises and their application. Examples of such influences are shown in Figure 1. Fire affects both the health of personnel and the functionality of objects within the vicinity of the fire. The nature of premises dictates the comparative risk of these factors. The recommendations given in Clause 4 of this British Standard are based on a holistic or balanced approach to the mitigation of fire risk in a range of premises. The recommendations address the risk of ignition, the spread and impact of fire following ignition, taking into account: product selection; installation of appropriate fire prevention, detection and suppression systems. Further recommendations relating to component selection are given in Clause 6, which may be implemented in isolation but only when the nature of the building or its occupancy does not allow for the balanced approach to be followed. The approach to fire safety in the design, management and use of buildings is defined by regulation and described in a number of documents including BS 9999 and the BS 7974 series. BS 8492 is intended to complement these regulations and standards. BSI

6 Figure 1 Examples of pathways in different types of premises 2 BSI 2009 Suspended ceiling Access floor Power cables Telecomms cables Wall ducts Older commercial offices, public buildings (airports, shops) Power cables Telecomms cables Telecomms cables No air-flow Newer commercial offices, general offices 1 Scope Lighting cables Telecomms cables Segregated power cables Computer rooms, data centres Cable in risers Large quantity of cables within forced air-flow compartments This British Standard gives recommendations for fire performance and fire protection of all types of telecommunications equipment and telecommunications cabling. It covers: a) designing and implementing cabling infrastructures; b) selecting products, including materials and construction; c) minimizing fire spread; d) increasing safety levels for personnel and property. This British Standard details the relationship between its recommendations, the usage of premises and fire protection measures. It is applicable to certain hazardous environments but does not exclude additional requirements which are applicable in particular circumstances, defined, for example, by electrified railways, petrochemical sites, intrinsically safe areas, explosive ordnance storage facilities (bomb dumps). NOTE Annex A considers the fire hazard posed by the installation of telecommunications equipment and telecommunications cabling infrastructure within premises.

7 It is expected that this British Standard will be of value to: 1) those responsible for specifying infrastructure solutions including: i) premises owners; ii) telecommunications consultants; 3) fire authorities; 4) those involved in installing fire prevention and protection systems. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. BS , Fire tests on building materials and structures Part 20: Methods for determination of the fire resistance of element of construction (general principles) BS , Fire detection and fire alarm systems for buildings Part 1: Code of practice for system design, installation, commissioning and maintenance BS 6266, Code of practice for fire protection for electronic equipment installations BS 6701, Telecommunications equipment and telecommunications cabling Specification for installation, operation and maintenance BS 7671, Requirements for electrical installations IEE Wiring Regulations BS EN , Fire resistance tests for service installations Part 3: Penetration seals BS EN (all parts), Information technology Cabling installation BS EN , Common test methods for cables under fire conditions Tests on gases evolved during combustion of materials from cables Part 2-1: Procedures Determination of the amount of halogen acid gas BS EN , Common test methods for cables under fire conditions Tests on gases evolved during combustion of materials from cables Part 2-2: Procedures Determination of degree of acidity of gases for materials by measuring ph and conductivity BS EN 50310, Application of equipotential bonding and earthing in buildings with information technology equipment BS EN , Measurement of smoke density of cables burning under defined conditions Part 2: Test procedure and requirements BS EN , Protection against lightning Part 4: Electrical and electronic systems within structures BS EN ISO 13943, Fire safety Vocabulary BSI

8 4 BSI Terms, definitions and abbreviations 3.1 Terms and definitions For the purposes of this British Standard, the terms and definitions given in BS 6701, BS EN (all parts), BS EN ISO 13943, and the following apply compartment discrete fire zone designed to contain a fire within that zone NOTE Compartments are also known as fire compartments compartmentation division of a premises into compartments in order to provide protection for the rest of the premises containment use of fire barriers or fire-stopping techniques to maintain the fire performance of defined compartments within the premises electric arc continuous, luminous discharge of electric current crossing a gap or an insulating surface between two conductors electric spark transient, luminous discharge of electric current crossing a gap or an insulating surface between two conductors plenum space where the primary purpose is the movement (typically forced) of air within which mains power cables, telecommunications cables and building services infrastructures can also be installed secondary ignition ignition of an item or items other than the original burning material telecommunications cabling infrastructure telecommunications cabling, closures, cable management systems and the cabinets, frames or racks within which closures can be installed telecommunications space specified volume associated with one or more termination points of telecommunications cabling 3.2 Abbreviations For the purposes of this British Standard, the abbreviations given in BS 6701, BS EN ISO and the following apply. MI MIMS PTFE upvc mineral-insulated (cable) mineral-insulated, metal-sheathed (cable) polytetrafluoroethylene unplasticized polyvinylchloride

9 4 Balanced approach to fire threat mitigation COMMENTARY ON CLAUSE 4 Clause 4 relates to the management of fire within premises and gives recommendations for the reduction of the risk of fire, and for the mitigation of the effects of fire, by the selection of suitable components and techniques for fire prevention, fire detection and fire suppression. The recommendations are based upon the consideration of the fire hazard posed by the installation of telecommunications equipment and cabling infrastructure within premises as described in Annex A, which addresses: a) ignitability; b) flame spread; c) heat release; d) the production of fire effluent (i.e. smoke, toxic gas and corrosive gas). The relative importance of these factors can differ throughout the areas served by the telecommunications cabling and associated infrastructure. Therefore, it is important to note that a single solution covering product selection, and containment, detection and suppression systems might not be appropriate. 4.1 General The balanced approach to fire threat mitigation detailed in 4.2, 4.3 and 4.4 should be applied, wherever practicable. The recommendations of Clause 4 are the primary approach in premises and should be used wherever practicable. Only where the balanced approach in premises is rendered impracticable or deemed inappropriate, owing to the nature of the building or its occupancy, should the recommendations of Clause 6 be considered in isolation. 4.2 Compartmentation within premises General Within the premises, compartments should be created that are separated by vertical and horizontal barriers with appropriate levels of fire performance in order to: a) prevent the spread of fire and its effluent; b) minimize the extent of loss. The selection of compartment boundaries should take into account the impact of fire within each compartment. The fire performance of items within each compartment, in combination with the fire detection and suppression systems of the compartment, should: 1) reflect the risk to property, personnel and business continuity; 2) be selected to satisfy the needs of the premises owners, landlords, tenants and insurers. NOTE Guidance on assessing risk is given in BSI

10 Table 1 Ranking of fire threats 6 BSI Risk management Ranking of fire threats WARNING. In cases where the location and contents of specific compartments remove the need to consider fire threats as described in Table 1, the maintenance of the boundaries of those compartments (i.e. containment) is critical to the fire performance of the premises as a whole. The fire threats specific to each compartment should be assessed in accordance with Table 1, which gives an indication of the degree of threat mitigation that is necessary in a variety of installations. Ranking General installations (see 4.4.2) Installations where evacuation of personnel is critical (see 4.4.3) Installations where protection of equipment is critical (see 4.4.4) Most important Resistance to ignition Resistance to ignition Resistance to ignition Flame spread Impact: Effluent: Smoke Impact: Effluent: Corrosive gas Impact: Effluent: Smoke Flame spread Flame spread Impact: Effluent: Corrosive gas Impact: Effluent: Toxic gas Impact: Effluent: Smoke Least important Impact: Effluent: Toxic gas Impact: Effluent: Corrosive gas Impact: Effluent: Toxic gas NOTE This table has been adapted from PD IEC/TR 62222:2005, Table Risk assessment and business continuity analysis A risk assessment should be carried out for each compartment which takes account of the following: a) architectural considerations; b) the fabric and contents of the compartment and building; c) the requirements of the owners, landlords, tenants and insurers, including for example; 1) protection of the building and its personnel; 2) business continuity; 3) aesthetics and finish; 4) electrical and optical performance of the cabling system. Where appropriate, business continuity analysis should also be applied. NOTE Recommendations for risk management are given in BS For guidance on business continuity, see BS

11 4.2.3 Telecommunications cabling infrastructure When installing telecommunications cabling infrastructure: a) where telecommunications cables are installed between compartments, appropriate fire stopping techniques should be applied at compartment boundaries in accordance with 5.1; b) in order to minimize transmission degradation, the introduction of joints within a cabling link should be avoided (other than those that might be necessary at, or close to, building entrance facilities where external cables are jointed to those more suitable for internal environments). NOTE Telecommunications cables may be installed in plenums that provide airflow to one or more compartments. The selection of a cable within a single compartment should be in accordance with the recommendations of 4.4. However, for cables that pass through several telecommunications spaces, the most economic solution might be to select a cable of lower fire performance consistent with the need to evacuate personnel (see Table 1) and either: 1) apply increased levels of fire protection in certain compartments served by that cable; or 2) create additional sub compartmentation in order to increase the level of fire protection. 4.3 Management of fire threats associated with telecommunications cabling infrastructure Fire hazards external to the telecommunications cabling infrastructure In areas beneath pathways containing large volumes of telecommunications cabling: a) suspended ceiling systems with defined fire performance should be installed and maintained in accordance with the manufacturer s/supplier s instructions; b) penetrations of suspended ceiling systems with defined fire performance should be fitted with fire barriers of equivalent performance. Storage facilities for combustible materials should not be located beneath or adjacent to main distribution pathways for telecommunications cabling unless appropriate compartmentation is applied. Floor and ceiling voids which house pathways containing large volumes of telecommunications cabling should be inspected and cleaned on a regular and monitored basis to prevent the accumulation of combustible material. BSI

12 8 BSI Heat sources within the telecommunications cabling infrastructure General The recommendations given in , and should be followed in order to avoid the common ignition phenomena encountered in electrotechnical products, which include abnormal temperature rises, short circuits, accidental electric sparks and electric arcs, and high transient peak currents. NOTE This information on common ignition phenomena is taken from IEC ) Telecommunications equipment The telecommunications equipment selected should: a) prevent ignition caused by an electrically energized component part; b) confine any fire that does occur within the bounds of the enclosure of the electrotechnical product; c) minimize flame spread beyond the product s enclosure; d) minimize harmful effects of fire effluents including heat, smoke, and toxic or corrosive combustion products. The telecommunications equipment should be installed, operated and maintained in accordance with BS Mains power cabling The mains power cabling connected to the telecommunications equipment should be installed, operated and maintained in accordance with BS Telecommunications cabling The telecommunications cabling should be installed, operated and maintained in accordance with BS The services, applications and networks supported by the telecommunications cabling should be restricted to those for which the cabling is specified. In addition, the following practices should be applied, as a minimum: a) lightning protection systems should be installed in accordance with BS EN ; b) surge protection should be installed in accordance with BS EN , the BS EN series and BS EN 50310; c) electrostatic charge management should be carried out in accordance with BS EN NOTE For telecommunications cabling that is intended to support applications that deliver power, guidance on implementation will be available in ISO/IEC TR 29125, once published. 1) In preparation.

13 COMMENTARY ON BS 7671 requires that precautions are taken such that cables or wiring systems cannot propagate flame. As a means of meeting this requirement, BS 7671 specifies that: a) cables not complying with the flame propagation requirements of BS EN are not installed between compartments (but are allowed for short lengths providing connection of appliances to the permanent wiring system); b) where a risk of flame propagation is high, the cable is to meet the flame propagation characteristics specified in the appropriate part of the BS EN series. BS EN or BS EN are seen to be appropriate for telecommunications cables. NOTE BS 7671 requires any non-compliance to be formally recorded in the Completion Certificate for the installation as exceptions with regard to spread of fire. BS 7671 also notes that the risk of flame propagation can be high where cables are bunched or installed in long vertical runs. This British Standard extends this consideration to all fixed telecommunications cables. BS EN requires that information technology cables that do not conform to BS EN ) are either: 1) terminated inside the building, within two metres (or an alternative distance if specified by local regulations) of the point of internal penetration of the fire barrier (e.g. floor/ceiling/wall); or 2) installed within trunking or conduit that is considered as a fire barrier in accordance with local fire regulations. Examples of cables that do not conform to BS EN include materials with minimal or no fire retardance (e.g. unmodified polyethylene) Fire load, flame spread and absence of oxygen Fire load The contribution of the telecommunications cabling infrastructure to the total fire load (see 6.1) of the premises should be minimized without jeopardizing functional and strategic objectives. Telecommunications cables and main power cables for telecommunications equipment that are no longer used should be removed Flame spread For a given cable, flame spread can be minimized if the telecommunications cables are closely bundled (see A.2, Note 2). However, the effect of such bundling on application support and the potential delivery of power should be taken into account (see ISO/IEC TR 29125). 2) Since the publication of BS 7671 and BS EN , it has been identified that BS EN does not contain normative requirements and therefore conformity with the standard is not applicable. It is anticipated that BS EN will be amended to clarify that the requirements in items 1) and 2) apply to information technology cables which do not meet the minimum recommended limits of BS EN BSI

14 10 BSI Absence of oxygen Fires will not occur or spread if oxygen is not available. The atmosphere in specific compartments may be modified to reduce the probability of ignition and the degree of flame spread. However, the application of such techniques is not generally applicable to telecommunications cabling infrastructures. 4.4 Additional measures based on installation type (see Table 1) General In addition to the recommendations given in 4.3, telecommunications cabling infrastructure installations should conform to 4.4.2, or 4.4.4, as appropriate to the type of installation (see Table 1) General installations NOTE 1 According to Table 1, the most important issue for these installations, after the prevention of ignition, is the reduction of flame spread. The reduction of the impact of effluents (smoke, corrosive gas and toxic gas) is considered to be of lower importance. To reduce the fire risk within a compartment, containment (see 5.1), detection (see 5.2) and suppression systems (see 5.3) should be applied such that the flame-spread properties of materials do not have to be considered. To reduce the flame spread between telecommunications spaces within a compartment (e.g. within plenums), one or more of the following approaches should be applied: a) the use of telecommunications cabling infrastructure materials that do not spread flame in accordance with 6.2.3; b) the use of telecommunications cabling infrastructure materials that minimize flame spread in accordance with 6.2.4; c) the use of other materials within an inert atmosphere or encased within non combustible materials (e.g. steel tubes). NOTE 2 The cost of products detailed in a) or b) generally tends to be higher than the cost of products with little or no resistance to ignition or flame spread and therefore, in some circumstances, the use of sub compartmentation together with containment, detection and suppression systems might be preferable. NOTE 3 The use of sub compartmentation together with containment, detection and suppression systems is appropriate where the required fire performance conflicts with the required transmission performance of the cabling components. Following the implementation of a balanced approach to control flame spread, the reduction of effluent production (see 6.4) should be addressed Installations where evacuation of personnel is critical NOTE 1 According to Table 1, the most important issue for these installations, after the prevention of ignition, is the reduction of smoke. A secondary issue is the reduction of flame spread. The reduction of the impact of the other fire effluent components (corrosive gas and toxic gas) is considered to be of lower importance.

15 To reduce the fire risk within a compartment, containment (see 5.1), detection (see 5.2) and suppression systems (see 5.3) should be applied such that the smoke-producing and flame-spread properties of materials do not have to be considered. To reduce the threat from smoke between telecommunications spaces within a compartment (e.g. within plenums), one or more of the following approaches should be applied: a) the use of telecommunications cabling infrastructure materials that do not spread flame in accordance with 6.2.3; b) the use of telecommunications cabling infrastructure materials that produce low levels of smoke effluent in accordance with ; c) the use of telecommunications cabling infrastructure materials that minimize flame spread in accordance with or 6.2.5; d) the use of other materials within an inert atmosphere or encased within non combustible materials (e.g. steel tubes). NOTE 2 The cost of products detailed in a), b) or c) generally tends to be higher than the cost of products with little or no resistance to ignition or flame spread and therefore, in some circumstances, the use of sub compartmentation together with containment, detection and suppression systems might be preferable. NOTE 3 The use of sub compartmentation together with containment, detection and suppression systems is appropriate where the required fire performance conflicts with the required transmission performance of the cabling components. Following the implementation of a balanced approach to control smoke production and flame spread, the reduction of toxic gas (see 6.4.3) and corrosive gas (see 6.4.4) should be addressed Installations where protection of equipment is critical NOTE 1 According to Table 1, the most important issue for these installations, after the prevention of ignition, is the reduction of corrosive gas. A secondary issue is the reduction of flame spread. The reduction of the impact of the other fire effluent components (smoke and toxic gas) is considered to be of lower importance. To reduce the fire risk within a compartment, containment (see 5.1), detection (see 5.2) and suppression systems (see 5.3) should be applied such that the corrosive-gas-producing and flame-spread properties of materials do not have to be considered. To reduce the threat from corrosive gas between telecommunications spaces within a compartment (e.g. within plenums), one or more of the following approaches should be applied: a) the use of telecommunications cabling infrastructure materials that do not spread flame in accordance with 6.2.3; b) the use of telecommunications cabling infrastructure materials that produce low amounts of corrosive gas when exposed to fire in accordance with 6.4.4; c) the use of telecommunications cabling infrastructure materials that minimize flame spread in accordance with or 6.2.5; d) the use of other materials within an inert atmosphere or encased within non combustible materials (e.g. steel tubes). BSI

16 12 BSI 2009 NOTE 2 The cost of products detailed in a), b) or c) generally tends to be higher than the cost of products with little or no resistance to ignition or flame spread and therefore, in some circumstances, the use of sub compartmentation together with containment, detection and suppression systems might be preferable. NOTE 3 The use of sub compartmentation together with containment, detection and suppression systems is appropriate where the required fire performance conflicts with the required transmission performance of the cabling components. Following the implementation of a balanced approach to control corrosive-gas production and flame spread, the reduction of smoke (see 6.4.2) and toxic gas (see 6.4.3) should be addressed. 5 Fire protection measures 5.1 Containment Specification of fire stopping techniques All cables and cable management systems passing through compartment boundaries (e.g. walls, floors or ceilings) should be protected by appropriate fire stopping techniques that reinstate the original fire rating of the boundary. NOTE Such techniques include fire-stopping materials and/or penetration sealing systems. Advice regarding the programming, installation sequence and suitability of particular fire stopping techniques should be sought from both the manufacturer and specialist contractors at the earliest possible opportunity in the construction phase. A fire stopping technique should be specified in terms of: a) the fire rating, construction details and orientation of the fire compartment structure [e.g. plasterboard wall (2 hour) or concrete floor (4 hour)]; b) the type and size of cable management system to be fire stopped and what it is manufactured from (e.g. 50 mm 50 mm PVC electrical trunking); c) where there is no cable management system, the size of the hole and the percentage of cable fill within the hole; d) where there is a cable management system, the size of the hole externally around the cable management system, the size of the hole internally within the cable management system and the percentage of cable fill within electrical trunking or conduit; e) a detailed description of the fire stopping system including any additional supports required for the cable system. The fire stopping technique applied should be proven to meet the specification criteria using the test methods given in BS EN and BS It is noted that a technique based upon interacting components should be regarded as a complete system and should only be used as such.

17 The telecommunications cabling system specifier should: 1) obtain documentary evidence from the manufacturer/supplier which defines the capability of the fire-stopping technique; 2) verify that the proposed specification is covered within the scope of this document; 3) ensure that the fire stopping technique is fit for purpose Installation of fire stopping techniques Fire stopping techniques should be installed in accordance with the manufacturer s/supplier s installation instructions. Each fire stop should be clearly labelled or otherwise marked to indicate its function so as to be identifiable during future cable installations. 5.2 Detection systems COMMENTARY ON 5.2 There are many active measures that can be implemented to warn occupants and building management about the existence of a fire and to change or modify the normal progress of a fire so that safety and loss reduction criteria can be satisfied. The detection system should detect fire at the earliest practicable moment and generate signals and indications in the form of an alarm so that appropriate action can be taken in order to preserve life and minimize loss. Fire detection and alarm systems should be designed, installed and maintained in accordance with BS Fire detection and fire alarm functions may be combined in a single system. Automatic fire detection and indication in dedicated electronic equipment areas should conform to BS A fire detection and alarm system may be linked to remote fault and fire alarm monitoring stations and to fire protection systems (e.g. compartmentalization, smoke control and fixed fire-fighting systems) which are designed to contain or extinguish the fire without further intervention. 5.3 Suppression systems COMMENTARY ON 5.3 Fire protection and suppression systems employed in normal commercial or industrial environments often use agents such as water, foam, or dry chemicals. Such agents would damage or destroy high value telecommunications equipment, so suppression systems in computer rooms, telecommunications rooms, and data centres usually employ either inert gaseous flooding agents or chemically active, gaseous suppression agents. The inert gaseous flooding agents all extinguish flames by cooling the flame gases (the thermal ballast effect due to dilution) below a critical temperature, which is dependent on the particular fuel and combustion situation. Chemically active, gaseous suppression agents (for example, halocarbons or halogenated agents) extinguish fires partly by chemical interaction with the combustion process and partly by flame cooling ( thermal BSI

18 14 BSI 2009 ballast effect). The concentration of the agent required is in the range of 5% to 15% of room volume and the agent discharge to reach this concentration takes 10 s to 20 s, generally with a further minute to ensure complete mixing and extinguishment. Agent delivery should be accomplished through well-designed detection and delivery subsystems. Any delay between the time that a fire is detected and the initiation of agent discharge should be minimized, consistent with the safe evacuation of personnel from any occupied area, in order to prevent the generation of damaging and/or toxic breakdown products, such as acid gases, from the agent and/or fire interaction. Activation of a gaseous suppression system usually results in an increase in the air pressure within the protected space. The spaces protected by gaseous fire suppression systems should not allow the fire-fighting agent to leak away, and in the case of rooms, integrity fan pressure testing should be carried out to ensure that this does not occur. 6 Fire threat mitigation by cabling component selection COMMENTARY ON CLAUSE 6 Clause 6 gives recommendations for the mitigation of fire risk by the selection of suitable components based upon the consideration of the fire hazard posed by the installation of telecommunications equipment and telecommunications cabling infrastructure within premises as described in Annex A, which addresses: a) ignitability; b) heat release; c) flame spread; d) the production of fire effluents (i.e. smoke, toxic gas and corrosive gas). This clause has been structured so that it is possible to implement the recommendations in isolation, where adoption of the balanced approach is deemed to be impracticable owing to the nature of the building or its occupancy. However, this needs to be given careful consideration. The recommendations may also be used in conjunction with the balanced approach. 6.1 General The levels of resistance to ignition, flame spread, heat release and fire effluent production that result from the materials selected should be in accordance with Table 2, based on the degree of threat mitigation. NOTE 1 The methods of achieving the specific levels for each parameter are described in 6.2, 6.3 and 6.4. NOTE 2 Guidance on the fire hazard of electrotechnical products is given in IEC and IEC ). 3) In preparation.

19 Table 2 Mitigation of fire threat Threat mitigation Applicable areas Resistance to ignition When selecting cabling materials, it is important to note that, for a given combustible material, a larger mass will result in: a) a larger and more intense fire; b) greater heat release; c) increased amounts of fire effluent. NOTE 3 For a given material, if the heat of combustion is known, the fire load is equal to the mass of that material multiplied by its heat of combustion. NOTE 4 For a fire scenario in which there are many different materials, each individual fire load is calculated and then they are summed to give the total fire load. Flame spread Heat release Smoke Impact Toxic effluent Corrosive effluent Very high All Very high None Very low Low See See High All High Very low Very low Medium Medium All High Low Low High Low All High Medium Medium NC Very low All Medium High High NC NOTE NC = not considered. 6.2 Ignition and flame spread NOTE 1 Guidance on ignitability is given in DD IEC/TS PD IEC/TR is a summary of ignitability test methods including comments on their relevance. NOTE 2 Guidance on flame spread is given in BS EN DD IEC/TS is a summary of surface spread of flame test methods including comments on their relevance General In the absence of other measures to limit the risk of ignition and restrict flame spread, the selection of materials for the telecommunications cables and cable management systems should follow the recommendations of to 6.2.6, as appropriate Thermoplastic materials Many of the materials used in telecommunications cabling infrastructure are thermoplastic. Some thermoplastic materials can produce molten flaming drips when ignited which then act as secondary ignition sources, thus spreading the fire. Such materials should be avoided. NOTE In fire tests thermoplastic materials have a tendency to melt away from the heat source (e.g. flame or hot wire) often resulting in non ignition, which can result in giving a false impression of a high resistance to ignition. Therefore, special considerations are given to the testing of the ignitability of thermoplastics (see BS ISO 10840). BSI

20 16 BSI Materials with very high resistance to ignition and no flame spread Where very high resistance to ignition and no flame spread is deemed appropriate (see Table 2), the materials of the telecommunications cabling and cable management systems should be non combustible, i.e. inorganic minerals and metals. NOTE 1 An example of this approach is bare, mineral-insulated, metal sheathed (MIMS) cable comprising copper conductors inside a metallic sheath, insulated by inorganic powder. MIMS cables are used to maintain critical electrical circuits that support the operation of telecommunications equipment during a fire. NOTE 2 Materials may be classified as non combustible if they have a gross heat of combustion of less than 2 kj g 1 as measured in a bomb calorimeter according to BS EN ISO NOTE 3 Some commonly used metals such as aluminium and iron can ignite and burn under extreme conditions, but only a pre existing fire of high intensity is likely to cause this to happen Materials with high resistance to ignition and very low flame spread Where high resistance to ignition and very low flame spread is deemed appropriate (see Table 2), the telecommunications cabling and cable management systems may use fluorinated polymers or other specialist polymeric compounds. NOTE Examples include: a) fully fluorinated fluoropolymers, e.g. polytetrafluroethylene (PTFE), and co-polymers of PTFE with other fully fluorinated monomers, e.g. hexafluoropropene. These are some of the most thermally stable polymers but tend to be limited to specialist telecommunications applications; b) more easily processed fluoropolymers, e.g. polyvinylidene fluoride and ethylenetetrafluoroethylene co-polymer (not fully fluorinated but maintaining a high resistance to ignition and exhibiting very low flame spread); c) unplasticized polyvinylchloride (upvc). The addition of plasticizers to make PVC more flexible, as required for use in telecommunications cables, generally reduces ignition resistance and increases flame spread, although this can be mitigated by the use of suitable materials; d) telecommunications cables that conform to BS EN These are usually based on insulation materials made from fluoropolymers or from specially formulated PVC materials; e) aromatic polymers such as poly-ether-ether-ketone and the aromatic polyimides. These have a high resistance to ignition but tend to be limited to specialist telecommunications applications Materials with high resistance to ignition and either low or medium flame spread Where high resistance to ignition and either low or medium flame spread is deemed appropriate (see Table 2), the selection of materials for the telecommunications cabling and cable management systems should take the following into account:

21 a) appropriate materials tend to be either those with an inherently low resistance to ignition or those which have been modified by the addition of flame retardants; b) two main types of flame retardant are used: 1) halogenated systems: halogens (chlorine or bromine) work by inhibiting the free radical combustion reactions that occur in flames; NOTE 1 Relatively low levels of addition (e.g. 15 wt%) can give moderate to good ignition resistance, and this means that the base properties of the matrix polymer are not compromised. NOTE 2 Antimony trioxide is often also used because it has a synergistic effect on the flame retardancy. 2) non halogenated systems: based on the addition of inorganic materials that decompose on heating to produce water and/or carbon dioxide; NOTE 3 The most common additive is aluminium hydroxide which decomposes to give aluminium oxide and water. These additives are not as efficient as halogenated systems; effective loadings are typically higher than 60 wt% and there is a considerable level of technical expertise involved to enable the production of effective formulations in which the properties of the matrix polymer are not compromised. This type of formulation was invented to avoid the problems associated with acid gas production which can occur when halogenated systems are forced to burn Materials with low resistance to ignition and high flame spread Where low resistance to ignition and high flame spread is deemed acceptable (see Table 2), the telecommunications cabling and cable management systems may use organic materials which are not inherently flame retarded or which contain no flame-retardant additives. 6.3 Impact: Heat release NOTE Guidance on heat release is given in BS EN PD IEC/TR is a summary of heat release test methods including comments on their relevance General In the absence of other measures to restrict heat release, the selection of materials for telecommunications cables and cable management systems should follow the recommendations of to 6.3.5, as appropriate Materials with very low heat release Where very low heat release is deemed appropriate (see Table 2), the materials of the telecommunications cabling and cable management systems should be non combustible, i.e. inorganic minerals and metals as detailed in BSI

22 18 BSI Materials with low heat release Where low heat release is deemed appropriate (see Table 2), the materials of the telecommunications cabling and cable management systems should have a low heat of combustion and a high resistance to ignition as detailed in Materials with medium heat release Where medium heat release is deemed appropriate (see Table 2), the materials of the telecommunications cabling and cable management systems should have either a low heat of combustion or a high resistance to ignition as detailed in Materials with high heat release Where high heat release is deemed acceptable (see Table 2), the telecommunications cabling and cable management systems may use materials with a high heat of combustion and no inherent or added flame retardancy, which are therefore easily ignited, as detailed in Impact: Fire effluent NOTE 1 Guidance on smoke obscuration is given in BS EN DD IEC/TS is a summary of smoke obscuration test methods including comments on their relevance. NOTE 2 Guidance on the corrosion damage effects of fire effluent is given in BS EN IEC/TS is a summary of test methods for the corrosion damage effects of fire effluent, including comments on their relevance. NOTE 3 Guidance on the toxicity of fire effluent is given in BS EN PD IEC/TR is a summary of toxicity test methods including comments on their relevance. DD IEC/TS describes the use and interpretation of toxicity test results General Halogenated fire retardants COMMENTARY ON The use of halogenated fire retardants within cable materials was introduced to increase ignition resistance, to reduce flame spread and to provide self extinguishing properties. When such products are the ignition source, this technology has been very effective in suppressing ignition and limiting subsequent fire development. However, when these products are subject to a fire that has started from another ignition source, and the halogenated materials are forced to burn, smoke production, acid gas production and carbon monoxide production all tend to be increased. As the use of halogenated fire retardants is a complex issue and depends on the fire scenario(s) of concern: a) the technical performance of the cable materials should be assessed in a fire hazard assessment before a selection is made; b) the requirements of the end-use application should be considered, e.g. the range of viable materials/products is likely to be restricted in circumstances where escape might be difficult, including premises such as sports stadia or hospitals, which are

23 intended to accommodate large numbers of visitors (who are unfamiliar with the fire escape routes) or where fire escape routes are constricted. NOTE Many organizations require the installation of low smoke / halogen free / zero halogen / low acid gas products. It is noted that these descriptions are marketing terms and a fire hazard assessment remains essential prior to product selection. Within the European cable industry BS EN , BS EN and BS EN are being used to describe low smoke, halogen free (LSHF) cables but as yet no defined requirements have been agreed Chemical composition of combustible materials As the chemical composition of the combustible material influences the composition of the fire effluent, the following should be taken into account: a) if the combustible material contains nitrogen (e.g. polyamides and polyurethanes), then hydrogen cyanide, oxides of nitrogen and acrylamides might be produced; b) if the combustible material contains sulfur (e.g. polysulfones), then sulfur dioxide and sulfurous or sulfuric acid might be produced; c) if the combustible material contains chlorine or bromine (e.g. PVC or polymers containing halogenated fire retardants), then halogen acids might be produced Material selection with regard to production of smoke General NOTE There are no standards based recommendations for product selection in relation to the levels of smoke production when cables burn. The effective mitigation of smoke production should be accomplished by limiting the risk of ignition and restricting flame spread, thus limiting the level of exposure to fire effluent. Where product selection alone is used to restrict of the amount of effluent, the materials for telecommunications cables and cable management systems should follow the recommendations of , or , as appropriate Materials with low smoke production Where low smoke production is deemed appropriate (see Table 2), the selection of materials for the telecommunications cabling and cable management systems should take the following into account: a) there are many products sold as low smoke (LS), low smoke and fume (LSF) or low smoke, zero halogen (LSOH), which are marketing terms that are undefined unless further reference is made to defined, relevant standard tests. For quantitative assessment, it should be determined whether the product meets defined requirements with respect to smoke production; b) within the European cable industry BS EN , BS EN and BS EN are being used to describe low smoke, halogen free (LSHF) cables but as yet no defined requirements have been agreed; BSI

24 20 BSI 2009 c) a minimum transmission value of 60% is the recommended default value for any cable when tested in accordance with BS EN ; d) when used in the area of fire threat, the terms given in items a) to c) indicate that, if the product is burned, the amount of smoke produced will be relatively small. However, the amount of smoke that is produced in a fire depends not only on the propensity of a product to produce smoke (as measured in a standard test), but also on how much of the product is burning and on the fire conditions, which might differ from the conditions used in the fire test. The reduction in visibility caused by smoke also depends on the volume into which the smoke is being dispersed. EXAMPLE Consider a cable which, when tested to BS EN and using nine 1 m lengths as the test specimen, gives a transmission value of 60%. If 90 m of this product are assumed to burn into a volume of 100 m 3, then the calculated visibility of a light emitting sign will be 17.4 m. Whereas, if 180 m of the product are assumed to burn into a volume of 50 m 3, the calculated visibility falls to 4.3 m. Details of this type of calculation are given in BS EN and in BS EN :2005, Annex A Materials with medium smoke production Where medium smoke production is deemed appropriate (see Table 2), the selection of telecommunications cabling and cable management systems should take the following into account. As with low smoke production, medium is a relative term. Generally, if materials burn in well ventilated conditions at high temperatures, then smoke production is moderate because combustion is relatively efficient and most of the carbon in the fuel will be oxidized to carbon dioxide Materials with high smoke production Where high smoke production is deemed appropriate (see Table 2), the selection of telecommunications cabling and cable management systems should take the following into account. Smoke production tends to be high when combustion is poorly ventilated or when non flaming pyrolysis is occurring. Products that contain halogenated fire retardants, which work by reducing the efficiency of combustion, also increase smoke production when forced to burn. Aromatic polymers also tend to produce more smoke than aliphatic polymers, e.g. polystyrene produces much more smoke than polyethylene when burned under the same conditions Material selection with regard to production of toxic gas COMMENTARY ON There is no evidence that fire effluent from electrotechnical products offers a greater toxic threat than the fire effluent from other products such as furnishings or building materials. All fire effluent is toxic and one of the most significant toxic components of fire effluent is carbon monoxide. The toxic significance of carbon monoxide is enhanced by the impact of other effluents, such as irritant gases, which could incapacitate personnel leading to increased carbon monoxide inhalation.