Guidelines in support to IEC 60079-17.pdf

Guidelines for managing inspection of Ex electrical equipment ignition risk in support of IEC 60079-17

GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17 First edition October 2008

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GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

CONTENTS Page Acknowledgements ................................................................................................................. vii Foreword ................................................................................................................................. viii Overview ....................................................................................................................................x 1

Introduction, scope and application ................................................................................. 1 1.1 Introduction................................................................................................................. 1 1.1.1 Objective ........................................................................................................ 3 1.1.2 Ex sampling strategy ....................................................................................... 3 1.2 Scope .......................................................................................................................... 4 1.3 Application .................................................................................................................. 5 1.3.1 Managing inspection of Ex electrical equipment ignition risk by applying gap analysis .................................................................................................... 6

2

Legislation, regulations and standards ............................................................................ 7 2.1 Introduction................................................................................................................. 7 2.2 The Health and Safety at Work etc. Act and Management of Health and Safety at Work Regulations ........................................................................................................ 7 2.3 ATEX 'Equipment Directive', ATEX 'Workplace Directive', The Equipment and Protective Systems for use in Potentially Explosive Atmospheres Regulations and The Dangerous Substances and Explosive Atmospheres Regulations ............................ 7 2.4 Provision and Use of Work Equipment Regulations ...................................................... 8 2.5 Offshore installations (Prevention of Fire and Explosion, and Emergency Response) Regulations.................................................................................................................. 8 2.6 Offshore Installations (Safety Case) Regulations ........................................................... 8 2.7 The Electricity at Work Regulations .............................................................................. 8 2.8 The Construction (Design and Management) Regulations ............................................ 9 2.9 IEC 60079-17 .............................................................................................................. 9 2.9.1 Maintenance .................................................................................................. 9 2.9.2 Inspection....................................................................................................... 9 2.9.3 Skilled personnel (electrical technicians) ........................................................ 10 2.9.4 Technical person with executive function...................................................... 10 2.10 ISO 2859-1 ................................................................................................................ 10

3

Applying SMS principles to managing the inspection of Ex electrical equipment ..... 12 3.1 Introduction............................................................................................................... 12 3.2 Policy ..................................................................................................................... 12 3.2.1 Initial inspection............................................................................................ 12 3.2.2 Periodic inspections ...................................................................................... 13 3.2.3 Sample inspections ....................................................................................... 14 3.2.4 Ex risk-based inspection ................................................................................ 16 3.2.5 Summary of coupling the sampling strategy with an RBI strategy.................. 17 3.2.6 Audit and review of Ex inspection strategy.................................................... 20 3.3 Organisation.............................................................................................................. 20 3.3.1 Roles and responsibilities .............................................................................. 20 3.3.2 Competence................................................................................................. 21 iii

GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

Contents Cont… 3.4

3.5 3.6

4

Planning and implementation .................................................................................... 22 3.4.1 Phase 1 of implementation plan ................................................................... 22 3.4.2 Phase 2 of implementation plan ................................................................... 23 3.4.3 Phase 3 of implementation plan ................................................................... 24 Measuring performance............................................................................................. 25 3.5.1 Initial Ex inspection target levels.................................................................... 25 3.5.2 Faults............................................................................................................ 25 Audit and review of performance .............................................................................. 25 3.6.1 Reviewing performance ................................................................................ 25 3.6.2 Auditing ....................................................................................................... 31

Managing inspection of Ex electrical equipment throughout its life cycle phases .... 32 4.1 Introduction............................................................................................................... 32 4.2 Design and construction ............................................................................................ 32 4.2.1 Equipment selection and implications for inspection and maintenance ......... 32 4.3 Installation/commissioning/handover ......................................................................... 33 4.3.1 Handover of data.......................................................................................... 33 4.3.2 Equipment register ....................................................................................... 33 4.3.3 Initial inspection............................................................................................ 34 4.4 Operation .................................................................................................................. 35 4.4.1 Equipment location....................................................................................... 35 4.5 Maintenance and inspection ...................................................................................... 36 4.5.1 Functional maintenance................................................................................ 36 4.5.2 Inspection of systems.................................................................................... 36 4.5.3 Efficiency in inspections ................................................................................ 37 4.6 Modification and decommissioning ........................................................................... 37

Annex A: Managing inspection of Ex electrical equipment ignition risk gap analysis checklist................................................................................................................... 38 A.1 Managing inspection of Ex electrical equipment ignition risk gap analysis checklist.... 38 Annex B: Developing sampling plans by applying the RBI sampling methodology......... 44 B.1 Introduction............................................................................................................... 44 B.2 Overview of developing a sampling plan by applying the RBI sampling strategy to manage Ex electrical equipment ignition risks ........................................................ 44 B.3 Steps in developing a sampling plan by applying the sampling methodology ............. 45 B.3.1 Define lots .................................................................................................... 45 B.3.2 Define grade of inspection............................................................................ 50 B.3.3 Define sample size ........................................................................................ 51 B.3.4 Define rejection criterion............................................................................... 55 B.3.5 Define frequency of inspection ..................................................................... 55 B.3.6 Select a random sample from a lot ............................................................... 59 B.3.7 Inspect sample.............................................................................................. 60 B.3.8 Record inspection data ................................................................................. 60 B.3.9 Define scoring and rules for handling faulty equipment ................................ 61 B.3.10 Audit and review of sampling plans .............................................................. 69 Annex C: Technical basis of RBI sampling methodology ..................................................... 70 C.1 Introduction............................................................................................................... 70 C.2 Limitations of inspection by sampling ........................................................................ 70 C.2.1 Varying ASLs and applying Pa(10%) and Pr(5%) for an example lot.............. 70 iv

GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

Contents Cont… C.3

C.4 C.5 C.6 C.7 C.8 C.9

Define key sampling parameters ................................................................................ 71 C.3.1 Calculation of P(X=d) using hypergeometric law ........................................... 71 C.3.2 Calculation of Pa(X=Re-1) using hypergeometric law .................................... 72 C.3.3 Calculation of P(X=d) and Pa(X=Re) using binomial law ................................ 72 Determination of Pa(10%) ......................................................................................... 73 C.4.1 Determination of Pa(10%) where n/N≥0,15.................................................. 73 C.4.2 Determination of Pa(10%) where n/N5 years old but ≤20 years old, and C >20 years old. Equipment age may affect its protection; where possible, such criteria should be referenced to design life. For simplicity and to avoid defining small lots, a pragmatic approach would be to select a single conservative age for all equipment on a particular installation, equal to the age of the installation. B.3.1.5 Define lots according to these criteria Ex electrical equipment should be allocated to lots using the criteria of B.3.1.1-B.3.1.4; to facilitate this, a matrix should be defined. The number of equipment in each lot will 47

GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

vary. See B.3.1.6 regarding exclusion of equipment from lots and assigning equipment to specific lots. Note that as more of the factors in B.3.1 are applied when determining lots the equipment will tend to be more homogeneous (e.g. same hazardous area classification, same type of protection, etc); however, this has the disadvantage of resulting in small lots (see B.3.3.4.6) except where the equipment is prevalent (e.g. junction boxes, luminaries, etc.). Users should carefully consider how to best define lots based on their portfolio of equipment, its location in installation areas, typical shutdown areas, etc. Some 80% of Ex electrical equipment in a typical installation may be located in Zone 2 hazardous areas: with such numbers, it should be beneficial to apply the sampling methodology. However, the number of Ex electrical equipment located in Zone 0 and Zone 1 hazardous areas of a typical installation may preclude application of the sampling methodology since lot sizes may be small, and more so once the additional criteria of B.3.1.2-B.3.1.4 are used to further subdivide the equipment into lots. See B.3.3.4.6 for further guidance on applying the sampling methodology to small lots. Following this process fully is likely to result in many small lots which is disadvantageous as it would require proportionately more inspection effort. The simplified approach to defining lots in the absence of appropriate Ex inspection records described in section 3.2.4 and Box 3.1 can be used as a reasonable starting point; this is based upon ignition risk which is itself determined by the probability of a flammable atmosphere being present (based on duration) and the probability of a source of ignition being present (based on electrical system rated currents). B.3.1.6 Exclusion of equipment from lots and assigning equipment to specific lots Some circumstances may preclude equipment from being allocated to lots and including it in a sampling plan. For example, where: C C

Specific grades and frequencies of inspection are required by overriding legislation, standards, etc. (e.g. for fire and gas detection equipment). The equipment design life is relatively short compared to the frequency of inspection such that it is unlikely to be inspected whilst in service.

Other circumstances may necessitate equipment being allocated to specific lots and including it in a sampling plan. This may apply to: C C C

Moveable electrical equipment (hand-held, portable and transportable), which may be used in various hazardous areas and is particularly prone to damage or misuse. Equipment with a particular safety integrity level (SIL) requirements. SCEs, which will be energised during emergencies (e.g. fire and gas detection equipment, emergency lighting, public address (PA), general alarm (GA), etc.) (see B.3.5.1).

Having such specific lots may facilitate allocation of a particular level of inspection proportionate to the additional equipment criticality. In addition, it ensures that some higher risk equipment is inspected, rather than it possibly not being randomly selected if part of a lot of mixed equipment. B.3.1.7 Examples of lots There are various possibilities as to how to define lots that meet the criteria of B.3.1. For example a lot could comprise mixed equipment (e.g. motors, junction boxes, luminaries, etc.) from a specific plant; defining such a lot has the advantage that in a shutdown, a sample of a mixture of equipment in that area is inspected. This also has the advantage 48

GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

of not introducing small lots for which applying the sampling methodology adds little value. Other factors that may determine the subdivision of equipment into lots include the installation size, shutdown areas, etc. Note that some equipment may need to be excluded from lots or assigned to specific lots; see B.3.1.6. Example Lots are defined for a 15 year old offshore installation by allocating Ex electrical equipment to a matrix using the following steps: C C

The installation is divided into three hazardous areas (Zone 0, Zone 1, Zone 2) and non-hazardous. Equipment in each sub area is divided into three types according to equipment electrical system rated currents.

This process is illustrated in Figure B.2 with equipment allocations summarised in a matrix (see Table B.1).

Three hazardous areas defined and non-hazardous: - Zone 0 - Zone 1 - Zone 2 - offshore non-hazardous

Hazardous area classification for installation: - Zone 0 - Zone 1 - Zone 2 - offshore non-hazardous

Zone 0

Zone 1

Zone 2

Electrical system rated currents: - intrinsically safe - instrumentation - HV/LV power circuits and emergency equipment

non-hazardous

Seven homogeneous lots defined (low, medium and high risk) see Table B.1

Figure B.2: Example of process for defining lots of Ex electrical equipment Note: In this example, Ex electrical equipment age and severity of the environment are the same.

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GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

Table B.1: Simplified approach to defining lots using a matrix for an offshore installation

Probability of source of ignition being present

Groupings of Ex electrical equipment based on electrical system rated currents

Onshore nonhazardous abnormal operations (Note 6)

Offshore nonhazardous abnormal operations (Note 6)

Intrinsically safe

Low

Instrumentation

Low

HV/LV power circuits and emergency equipment

Medium

Probability of flammable atmosphere being present Zone 2 Low (Note 3) Low (Note 3) Medium (Note 3)

Zone 1

Zone 0

Low

Low

Medium

N/A (Note 4)

High

N/A (Note 4)

Notes: 1 Table B.1 is an example based on Table 3.1; clearly, the ‘onshore non-hazardous’ column is not relevant. 2 Greyed-out cells indicate where there is no such Ex electrical equipment at this installation. 3 Most of the inventory of Ex electrical equipment is located in Zone 2; in the absence of historical records, this approach provides a reasonable starting point in determining lots. However, where records exist, the next step should be to apply the full criteria for defining lots set out in B.3.1.1-B.3.1.4 for Ex electrical equipment located in Zone 2. 4 N/A – Such Ex electrical equipment is not appropriate for that zone. 5 For this offshore installation with several thousand Ex electrical equipment, seven lots would be defined: four low risk; two medium risk; and one high risk. Whereas, for a smaller installation with much less Ex electrical equipment, the four low risk lots may be grouped into one low risk lot, and similarly, the two medium risk lots may be grouped to one medium risk lot. 6 In abnormal operations a flammable atmosphere may be present in areas designated non-hazardous in normal operations; some electrical equipment may be required to be in service then such that it should be Ex electrical equipment. Offshore accommodation platforms have emergency lighting that would be expected to operate in abnormal operations.

B.3.2

Define grade of inspection The grade of inspection should be defined: C C

close inspection, and detailed inspection.

The findings of initial and periodic inspection findings (e.g. visual inspection, close inspection) should be considered when developing a sampling plan. These findings may enable application of the sampling methodology to either or both detailed inspection and close inspection. Developing sampling plans for detailed inspection and/or close inspection should constitute only part of an overall Ex inspection strategy (see section 3.2). Such a strategy also should include visual inspection (for which sampling should not be applied), and detailed inspection and/or close inspection of equipment for which sampling is not applied (e.g. due to small lots, etc.).

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GUIDELINES FOR MANAGING INSPECTION OF EX ELECTRICAL EQUIPMENT IGNITION RISK IN SUPPORT OF IEC 60079-17

B.3.3

Define sample size Once lots have been defined, the rest of the sampling methodology is applied to each lot such that a series of sampling plans are defined. The next step in the sampling methodology is to define the sample size for each lot, which is the number of random equipment that should be selected from each complete lot for inspection. Four main criteria are required to define the sample size of a lot: C lot size (see B.3.3.1); C global failure rate (see B.3.3.2); C category of inspection (see B.3.3.3), and C ASL (see B.3.3.4).

B.3.3.1 Define lot size The lot size is the number of equipment in a lot. It is determined using the equipment register (e.g. a CMMS). The lot size should be adapted according to the confidence in the exhaustiveness of the database. Lot size should be defined in the following ranges of number of equipment: C