ATLAS clarifies how risk assessments should be performed under BS EN 62305

(03/12/2008)

Contractors in the lightning protection industry may have received correspondence regarding “official risk assessment software” for BS EN 62305. The ATLAS Lightning Conductor Committee are concerned that this correspondence may have caused confusion as to the manner in which risk assessments should be performed under BS EN 62305 and as the trade body for the industry ATLAS have issued this Technical Update with a view to ensuring best practice in the industry.

The position is this; the IEC published their version of 62305 which includes Annex J “Simplified software for risk assessment for structures” (SIRAC). CENELEC adopted IEC 62305 in its entirety and as such the British and other National Standards Institutions of member states of the European Union are bound to withdraw their own like standards and adopt the CENELEC standard subject to certain permitted variations as referred to below.

Although the IEC Technical Committee were hoping to publish a universal standard that would be appropriate to all countries throughout the world, it became apparent during the process of compiling the standard that this was not going to be achievable. Factors such as each countries perception of risk along with the fact that lightning activity can vary significantly from country to country meant there needed to be variable parameters that took into account different countries’ needs.

It was thus concluded that each National Committee could decide certain parameters within their own National Standard (see Annex NC). In the exercise of this discretion the British Technical Committee responsible for BS EN 62305 (GEL 81) decided to vary certain of the parameters prior to publishing the BS EN 62305 in September 2006. These changes were primarily related to the tolerable risks of R2 and R3 (10-3 EN value, 10-4 BS value) and an amplification of the table C.1 Lf values to include many more typical mean values than the few examples shown in the IEC and CENELEC versions. Table NC6 was also modified to broaden the understanding of what qualified for risk of loss of service to the public.

The confusion that appears at the moment is largely related to the risk assessment itself and the status of the SIRAC software. The SIRAC software is indeed part of BS EN 62305 by virtue of the fact that within the bureaucratic IEC/CENELEC parallel voting rules the SIRAC software was adopted by IEC, which automatically meant it was adopted by CENELEC and in turn was automatically adopted by the National Standards. The software which is available for purchase from BSI comprises this SIRAC software.

However it should be approached with extreme caution as the sole use of this software in determining risk according to BS EN 62305 will give an incorrect assessment which could potentially expose contractors to liability on the grounds of professional negligence.

Why? The answer becomes clear if time is taken to read and understand the relevant standard in detail; Annex J of Part 2 gives the answers.

Annex J, on page 104 of the IEC standard, which is identical in the CENELEC & BS versions of the standard states “The calculator is designed to be relatively intuitive for users wishing to obtain an initial assessment of risk sensitivity”. It furthermore states variously that “The purpose and limitations of SIRAC are as follows;
• The software does not implement the full functionality of this standard as such an implementation would have added unintended complexity to the tool. Users are encouraged to use the written standard for a more detailed treatment of risk...
• It is applicable only for the calculation of single zone structures.
• SIRAC should be viewed as a companion tool to IEC 62305-2...”

In addition to the above clearly acknowledged limitations of the SIRAC software it is of fundamental importance that users of the SIRAC software appreciate that the software is in practice only compatible with the IEC and CENELEC versions of the standard. This is due to the fact that the SIRAC software utilises certain embedded coefficient values that are not applicable in respect of the British standard, as a result of the permitted variations adopted in BS EN 62305 referred to above. Furthermore even when used in conjunction with the IEC and CENELEC standards, as can be seen from the extracts from Annex J set out above, it is at best a non-comprehensive support style guide since it does not account for many areas needing consideration when applying the requirements of the standard properly and fully.

In order to avert any suggestion that contractors have failed to exercise the skill and care expected of them, when undertaking risk assessments under BS EN 62305 ATLAS would encourage its members to follow the recommendations set out in Annex J. This would entail ensuring that all parts of the risk assessment process are considered, not just those areas addressed within the SIRAC software.

It is possible to undertake the full risk assessment process manually but, as those of you who are familiar with the process will know, this is not a quick task. An alternative to this manual process is the use of bespoke software that takes account of the full functionality of Part 2 of the standard and not just the areas that SIRAC covers. Should you choose to use software when carrying out a risk assessment under BS EN 62305, it is in ATLAS’ view important to ensure that the software you use takes account of the full requirements of the standard and utilises the correct values and extent of the British National Annexes NB and NC.

You are advised to take extreme caution not to mislead either yourselves or your clients by only taking account of the SIRAC assessment results when calculating risk to BS EN 62305, it will NOT take account of the full requirements of the standard and so will not provide an accurate result under that standard.

If you require any further clarification of the above, send your specific query to the Secretariat and the LC committee will endeavour to furnish a response.

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