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THIS ARTICLE exposes a worrying contradiction in the UK Building Regulations concerning the � re safety requirements of protected electrical

circuits, which has serious consequences for the performance of all life safety and � re� ghting systems required to protect life and minimise property damage in buildings. This potentially dangerous contradiction not only impacts the performance of the very safety systems needed to protect life and property, but probably has further underwriting and potential legal implications.

Life safety and � re� ghting systems include, but are not limited to: � re alarms; evacuation (EWIS) systems; fireman’s lift submains; electric fire suppression pump submains; smoke and heat extraction and pressurisation fans; power and control circuits; and emergency lighting. These circuits are often fed by consumers’ mains and submains circuits which should, by de� nition, also be considered as protected circuits.

There are also important shortcomings and omissions within British and EN/IEC standards concerning the � ammability of electrical cables, smoke emission tests for cables and the generation of toxic by-products of combustion. Approved Document B (Fire Safety) of the Building Regulations [ADB] adopts the standard time temperature protocol of BS 476 part 21 for load bearing elements, part 22 for non load

bearing elements, part 23 for � re protecting suspended ceilings and part 24 for ventilation ducts.

This time temperature test protocol is also known as ISO 834-1, EN 1363-1, DIN 4102 and AS/NZS 1530 part 4, and is commonly called the ‘Standard Time Temperature Curve’ or ‘Cellulosic Curve’. This test requirement is used in BS EN 1634 for testing fire doors and associated hardware, � re stopping systems for penetrations, and in fact every single structure, material, component and product that is required to have a � re resistance rating by the Building Regulations.

It is then both surprising and concerning that the only single exception for any structure, element, material or product required to have a � re resistance rating in the Building Regulations is the very electrical cables that enable and form an integral part of all the critical life safety and firefighting systems needed to ensure safe evacuation of people and effective � re� ghting interventions.

These essential cables are allowed to be tested to di� erent standards which are not representative of known building � re pro� les, and in cases at signi� cantly lower fire temperatures by the British Standards Institute (BSI) standards listed and referenced in the Building Regulations. One example is ‘protected power circuits’, clause 5.38, page 57 of ADB.

Short circuitRichard Hosier examines whether the UK Building Regulations properly cover protected electrical circuits in terms of fire safety

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Testing protocols

It is noteworthy to benchmark what test protocols other developed countries adopt and mandate in their building codes for essential life safety and �re�ghting electrical wiring systems. Germany, Belgium, Australia, New Zealand, America and Canada all require that the electrical cables and wiring systems which need to maintain electrical integrity during �re be tested and certified to exactly the same fire time temperature protocol as every other element, structure, component or system in the building.

This is the ‘Cellulosic Curve’ of ISO 834-1; EN 1363-1; BS 476 parts 21, 22 ,23 and 24; DIN 4102; AS/NZ S1530 part 4; and in the case of the USA and Canada, ASTM E119-75 and NFPA 251 (which are almost identical). There is no reason whatsoever that the most important electrical circuits in buildings cannot be made and tested in Britain to the same test protocol as all other �re resisting elements of a building, because hundreds of cable manufacturers around the world already manufacture and successfully test cables meeting these tests.

Our company – MICC Ltd – is one, and we point out that all the major international cable manufacturers active in the UK market already make these cables for those countries, which require a common fire resistance rating for all elements, products, systems and components of a building. We also note that this ‘Standard Time Temperature’ protocol is adopted into the building codes of virtually every country in the world where �re resistance of structures, components, products and systems is required.

Fundamentally, the di�erence between the �ame tests referenced in today’s BSI standards for fire resistant cables – and the �re tests used for every other component structure product and system – is that cable tests in Britain today are simple �ame tests on the cables only, whereas BS 476 parts 21-24 require a furnace test which tests not only the cables, but also their associated �xings, supports and, where necessary, joints.

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Of note also is the fact that the �ame temperatures in the BSI tests for these essential cables are at lower �nal temperatures than those required in the full scale furnace testing to BS 476 parts 21-24, which in itself is a concern given that the cables and their �xings are likely to be in the same fire as every other structure, component, product and system.

We are also obliged to test our cables to these simple BSI �ame tests, but we have additionally opted to test our cables to the more stringent protocols of the furnace tests, because we take seriously our responsibility to provide a fit for purpose product. However, we remain concerned that these simple �ame tests, which are adopted into all BSI standards where �re resistance of electrical wiring systems is required, are inadequate and contradict. In fact, they seem to be tests that the cables can pass, rather than tests the cables should pass.

Findings and response

Our observations on this important anomaly have been raised with BSI a number of times, but the response has generally been:

• BSI standards are minimum and not maximumrequirements• The Building Regulations adopt the respectiveBSI standards• The tests on cables have been developed to testelectrical integrity under conditions of voltage andcurrent in �ame with water and mechanicalimpacts, which is not possible in furnace tests

In contradiction to these arguments, Australia, New Zealand, America, Canada, Germany and Belgium all successfully test electrical cables in furnace conditions under conditions of voltage and current with realistic mechanical stresses during �re, and for the e�ect of water spray simulating sprinklers and firefighting activities. In addition, these countries test not only the cables, but also all the support and �xing systems together, as these form an integral part of the wiring system, which current BSI standards do not.

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Further, the BSI standards technical committees responsible for drafting these standards often have representation from the very cable manufacturers which develop the test methods adopted. We remain unconvinced that the BSI technical committees responsible for drafting these cable �re test standards have sufficient industry diversity or international best practice experience.

As an example, we reference BS 8519: 2010, which in turn references BS EN 50200: 2006, BS 8434-2: 2003 + A2: 2009 and BS 8491: 2008 – all of which have di�erent test temperatures and methodology for testing cables in �ame. We also point to clause 19, where this same standard requires junction boxes joining fire resistant cables of protected circuits to be tested to the principals of BS EN 1366-5, which adopts the furnace test of the ‘Standard Time Temperature’ protocol of BS 476 parts 21-24, ISO 834-1 and EN 1363-1.

Having Building Regulations that allow two or more di�erent test protocols for �re resistance testing – and speci�cally an arguably inferior test protocol for the very cables that are needed to ensure reliability and e�ectiveness of all life safety and �re�ghting systems, especially as the essential �xings and supports are not required to be tested – would probably present di�culties if challenged in a legal or underwriting context.

Unrepresentative?

With regard to British and IEC standards for fire performance testing, we note that BS 4066-3 (IEC 60332-3) may be unrepresentative for �ame retardance testing of cables due to the fact that this test method does not require preconditioning of cable samples to their maximum operating temperature. BS 7671 (IEE Wiring Regulations) allows speci�c cables to operate with current ratings inducing conductor temperatures to 90°C. The temperature index (temperature at which a material will self support combustion in a 21% oxygen atmosphere) of a material will signi�cantly reduce at higher temperatures. Because of this, we believe there is a likely mismatch between these standards, which could well be misleading the market.

BS 8491: 2008 harmonised with IEC 61034 requires smoke obscuration testing by burning cable samples in an alcohol flame. It does not require testing in a non flaming mode. Many common insulating materials generate signi�cantly more smoke in a non �aming mode than in a �aming mode. Thus users of this standard are often misled into thinking the cable materials they buy are low smoke, and in many cases (short circuit/overload, incomplete burning, high heat), this can be quite the opposite.

BS 6425-1 (IEC 60754.1) is a test for halogens in polymeric materials. This test is speci�ed widely in the UK and around the world, with many manufacturers, consultants and authorities believing halogen free materials will be safer. In fact what often happens in the market is that manufacturers then manufacture

halogen free cables with polyethylene insulation, which is halogen free, but which due to its extremely high calori�c value, generates significantly more heat, eats more oxygen and can produce large volumes of toxic carbon monoxide (CO), especially during burning in reduced oxygen environments, such as most building �res.

Responsibility

Whilst CO is not a halogen gas, it is highly toxic and is claimed to be responsible for most toxicity deaths in fires (note that the increase in man made fibres, lightweight building materials and plastics is reported to be increasing the amount of hydrogen cyanide generated in modern building �res). Further, it is well documented and reported that electrical wires can and have caused �re due to short circuit or overload.

Despite this fact being well known and published, there is not one single mandatory test on electric cables for ignition under short circuit and overload conditions. Tests conducted by Nexans and published in a Jicable conference report in June 2011 show clearly that polymeric cables with XLPE insulations (meeting BS 4066-3/IEC 60332-3) can, under uncleared short circuits, self ignite within 60 seconds when subjected to gross overloads.

It would appear that an urgent case for a review of ADB is needed to harmonise �re resistance testing protocols to include protected electrical circuits. In addition, BSI needs to review the industry diversity and experience of its technical committees to ensure its standards provide the British public and the institutions that adopt them with relevant, robust and appropriate standards which, wherever possible, adopt world best practice

Richard Hosier is Asia/Pacific regional manager at MICC Ltd. For more information, view page 5

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