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Health and Safety Executive

Revised land use planning arrangements around large scale petroleum depots Prepared by Environmental Resources Management Ltd for the Health and Safety Executive 2007

RR511 Research Report

Health and Safety Executive

Revised land use planning arrangements around large scale petroleum depots Dr Andrew Franks CEng MIChemE Environmental Resources Management Ltd Manchester Office Suite 8.01 8 Exchange Quay Manchester M5 3EJ

Following the incident at the Buncefield Oil Storage Depot in December 2005, the Health and Safety Executive (HSE) commissioned Environmental Resources Management (ERM) to assist in reviewing HSE’s approach to providing landuse planning (LUP) advice in the vicinity of similar installations.

Proposals for revised arrangements for provision of LUP advice have been developed. Two options are presented. The proposals are based on a review of information on the effect of blast on building occupants, observations of the blast damage at Buncefield, and a review of some of the justification underpinning certain aspects of the current arrangements. Both of the options proposed would result in greater restriction on development of land in the vicinity of those sites affected.

For both options, the proposed system would operate within a defined geographical area around affected sites. The sensitivity of the size of this area to certain factors has been investigated.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

HSE Books

© Crown copyright 2007

First published 2007

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Applications for reproduction should be made in writing to:

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or by email to [email protected]

Acknowledgements

The assistance of personnel in HSE’s Hazardous Installations Directorate, and in particular Dr David Painter and Mr John Murray, is gratefully acknowledged.

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CONTENTS

CONTENTS III

EXECUTIVE SUMMARY V

1 INTRODUCTION 1

2 CURRENT ARRANGEMENTS 2

2.1 LAND USE PLANNING ZONES 2

2.2 DEVELOPMENT TYPES AND HSE’S ADVICE 4

3 REQUIREMENT FOR REVIEW OF CURRENT ARRANGEMENTS 8

4 OBJECTIVE OF REVISED ARRANGEMENTS 10

5 OPTIONS FOR REVISED LUP ARRANGEMENTS 11

5.1 CHANGES TO LUP ZONES 15

5.2 CHANGES TO SENSITIVITY LEVEL DEFINITIONS 15

6 DEVELOPMENT OF PROPOSALS FOR REVISED ARRANGEMENTS 16

6.1 REVISION OF LUP ZONE BOUNDARIES 16

6.2 REVISION OF SENSITIVITY LEVEL DEFINITIONS 17

6.2.1 Small housing, hotel / hostel and retail / leisure developments 17

6.2.2 Workplaces 19

6.2.3 Summary of Recommendations 20

6.3 OPTIONS 20

6.4 APPLICATION 20

7 IMPACT OF THE PROPOSED ARRANGEMENTS 21

7.1 SUMMARY OF IMPACTS 44

7.2 ADVANTAGES AND DISADVANTAGES 44

8 SENSITIVITY 46

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8.1 SOURCE TERM 46

8.1.1 Sensitivity to Source Geometry 47

8.1.2 Sensitivity to Fuel Composition 50

8.2 VAPOUR DISPERSION 50

8.2.1 Release Duration 51

8.2.2 Topography 51

8.2.3 Weather 51

8.2.4 Presence of Ignition Sources 51

8.2.5 Source Term 51

8.3 EXPLOSION PROPERTIES 52

8.3.1 Explosion Size 52

8.3.2 Explosion Strength 54

8.4 SUMMARY 56

9 SUMMARY AND CONCLUSIONS 59

10 REFERENCES 61

APPENDIX 1 REVIEW OF RESEARCH ON EXPLOSION EFFECTS 62

APPENDIX 2 BUILDING DAMAGE OBSERVATIONS 69

APPENDIX 3 ESTABLISHING REVISED ZONE BOUNDARIES 75

APPENDIX 4 CASE SOCIETAL CONCERNS - WORKPLACES 78

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EXECUTIVE SUMMARY

Following the incident at the Buncefield Oil Storage Depot in December 2005, the Health and Safety Executive (HSE) commissioned Environmental Resources Management (ERM) to assist in reviewing HSE’s approach to providing land-use planning (LUP) advice in the vicinity of similar installations.

At the time of writing the detailed causes of the incident are still under investigation, although a series of reports have been published by the Major Incident Investigation Board (MIIB) (MIIB, 2006a; MIIB, 2006b; MIIB, 2006c; MIIB, 2006d).

The work performed by ERM has comprised the following:

• performing a review of the current LUP arrangements; • consideration of the various options for revised LUP arrangements in the light of the

experiences at Buncefield; • development of the selected options for revised arrangements; • investigation of the impact of the proposed revised arrangements upon the LUP advice

provided by HSE to local authorities; and, • examination of the sensitivity of the proposed options to a range of factors associated

with the features of the major hazard sites of interest.

The Health and Safety Executive (HSE) provides land use planning (LUP) advice to local authorities regarding applications for development in the vicinity of major hazard installations and major hazard pipelines. This report relates only to HSE’s approach to providing LUP advice around major hazard installations.

At present HSE employs a system for determining the advice to be given that comprises the following elements:

• establishing three concentric (but not necessarily circular) zones around the site in question, termed the inner, middle and outer zones;

• assigning development proposals to one of four ‘Sensitivity Levels’; and, • determining the advice to be given by essentially using a matrix that shows which

development Sensitivity Levels are considered by HSE to be inadvisable in which zones.

For major hazard sites handling or storing flammable substances a ‘protection based’ approach is used to determine the zone boundaries. In most cases the protection based approach involves considering the consequences of a selected event. Zone boundaries are set at the range to different levels of harm that would be expected to result from the event:

• the boundary between the inner and middle zones is usually set at the range at which

members of a typical population could be subjected to a level of harm corresponding to

a significant likelihood of death;

• the boundary between the middle and outer zones is usually set at the range at which a

typical, exposed population could experience a dangerous dose;

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• the outermost edge of the outer zone is usually set at the range at which a sensitive or vulnerable population could experience a dangerous dose.

The requirement for review of the current arrangements arises from the experience of the Buncefield incident. As a result of the MIIB investigations, it is known that:

• a storage tank was filled to overflowing with petrol; • as the petrol overflowed from the tank a substantial vapour cloud was generated; • the vapour cloud spread over parts of the site and to areas beyond the site boundary; • the vapour cloud was ignited, resulting in a vapour cloud explosion (VCE); and, • the VCE caused extensive damage to buildings, particularly those close to the site of the

explosion.

At present it is not clear why the vapour cloud exploded with such force. Although accidents involving VCEs have occurred before and the VCE phenomenon has been the subject of much scientific investigation, an explanation for the strength of the VCE experienced at Buncefield is currently lacking.

At present HSE performs protection based assessments of sites like that at Buncefield (storage facilities for petroleum products). This assessment involves considering the potential for a VCE. However, on the basis of current scientific understanding of the way in which VCEs occur, the potential for a VCE at a site like Buncefield would be limited to those parts of the facility that provided sufficient confinement or congestion to generate a VCE, such as the tanker loading rack, giving rise to relatively small hazard ranges. The protection based assessment would therefore be likely to be based on other hazards, typically large pool fires.

Proposals have been developed for revised arrangements for HSE’s provision of LUP advice. The proposals have been developed by:

• reviewing published HSE research on the effects of explosions (Jeffries et al., 1997; Galbraith 1998);

• considering the levels of damage to buildings observed around the Buncefield site; • considering the principles upon which HSE’s advice is based; and, • revisiting the justifications underlying the Sensitivity Level definitions for proposed

developments in the light of the other activities.

The specific objectives of the proposed revised arrangements are to:

• establish LUP zone boundaries that take into account observations arising from the Buncefield incident; and,

• provide a decision making framework for use with the revised LUP zones that takes into account the particular nature of the VCE hazard.

The proposed arrangements are protection based. The objective of this and other protection based approaches is to:

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“achieve a separation between developments and the site which provides a very high degree of protection against the more likely smaller events, whilst also giving very worthwhile (sometimes almost total) protection against unlikely but foreseeable larger-scale events.” (HSE, 1989).

It is not the objective of the proposed arrangements to provide complete protection for future developments from damage, or for their occupants from harm. Neither is it the objective of the proposed arrangements to suggest what should be done about existing land use around affected sites.

It was judged that any revised approach should have regard for the current state of knowledge regarding events at Buncefield, and should be somewhat precautionary in nature.

Two options are presented:

• Option A: On the basis of blast damage observations at Buncefield, increase the size of the LUP zones only; or,

• Option B: Increase the size of the LUP zones and revise the development Sensitivity Levels.

Under the current system the Buncefield site has the inner, middle and outer zone boundaries set at distances of 120 m, 135 m and 185 m respectively. The proposed system would increase these distances to 250 m, 300 m and 400 m respectively.

The proposed changes to the Sensitivity Levels under Option B would place greater restrictions on the types of development that HSE would not advise against in the inner zone.

It is recommended that the proposed arrangements are applied to those sites which are similar to Buncefield in a number of important respects. These similarities would indicate that on the basis of what is known at present, the site has the potential to give rise to a comparable VCE.

If implemented, it is recommended that the proposed arrangements are applied to sites with the following characteristics:

• the site is classed as either ‘upper tier’ or ‘lower tier’ under the Control of major

Accident Hazards Regulations 1999 (the COMAH Regulations);

• the site stores petroleum in vertical, cylindrical, non-refrigerated above-ground storage tanks with side walls greater than 5 m in height; and,

• the filling rate of the storage tanks is greater than 100 m3 / hour.

These criteria align with those used by the Buncefield Standards Task Group, a joint COMAH Competent Authority and Industry committee (HSE, 2006).

In comparison with the current system, the proposed changes will, if implemented, result in:

• significantly larger zones for the sites affected (for both Options A and B);

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• as a result of the increased area within the zones, a larger number of consultations concerning proposed developments in the vicinity of affected sites (for both Options A and B); and,

• more restrictive advice concerning developments in the inner zone (for Option B).

Furthermore, it is recognised that there may be significant implications in the proposed system for other types of site. These sites include bulk LPG (liquefied petroleum gas) storage, gasholders, other flammable liquid storage and other facilities presenting a hazard with an associated significant likelihood of death in the inner zone (including VCEs and other hazards such as fireballs). A review of the implications of the study findings for LUP arrangements applicable to other types of site is recommended.

An investigation of the sensitivity of the size of the proposed LUP zone boundaries to various factors was undertaken. The factors considered included:

• the rate at which vapour is formed and the conditions under which this occurs (the source term);

• the way in which the cloud moves (the dispersion of the vapour); • the quantity of fuel involved in the explosion (the explosion size); and, • the violence of the explosion (the explosion strength).

The factors considered to have the greatest influence on the size of the zones were:

• the geometry of the storage tanks at the site (this affects the way the liquid contents behave in the event of a tank being overfilled);

• the duration of a release (this affects the size of the flammable vapour cloud formed); • the topography of the tank surroundings (features in the surroundings such as slopes and

obstacles have a marked effect on the behaviour of the vapour cloud); and, • the weather conditions at the time that a release occurs (calm, low wind speed

conditions favour formation of a large cloud).

It is important to note that:

• several of these factors (tank geometry, time to ignition and topography) are strongly site-specific;

• it is conceivable that a combination of differences in these factors could lead to an explosion with more serious consequences than Buncefield;

• in the time available it has not been possible to quantify the impact of all of these factors on land-use planning zone boundaries; and,

• the reasons for the strength of the explosion at Buncefield are not yet understood, further investigation may indicate that there are additional factors that are important.

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1 INTRODUCTION

Following the incident at the Buncefield Oil Storage Depot in December 2005, the Health and Safety Executive (HSE) commissioned Environmental Resources Management (ERM) to assist in reviewing HSE’s approach to providing land-use planning (LUP) advice in the vicinity of similar installations.

At the time of writing the detailed causes of the incident are still under investigation, although a series of reports have been published by the Major Incident Investigation Board (MIIB) (MIIB, 2006a; MIIB, 2006b; MIIB, 2006c; MIIB, 2006d).

The work performed by ERM has comprised the following:

• Performing a review of the current LUP arrangements; • Consideration of the various options for revised LUP arrangements in the light of the

experiences at Buncefield; • Development of the selected options for revised arrangements; • Investigation of the impact of the proposed revised arrangements upon the LUP advice

provided by HSE to local authorities; and, • Examination of the sensitivity of the proposed options to a range of factors associated

with the features of the major hazard sites of interest.

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2 CURRENT ARRANGEMENTS

The Health and Safety Executive (HSE) provides land use planning (LUP) advice to local authorities regarding applications for development in the vicinity of major hazard installations and major hazard pipelines. This report relates only to HSE’s approach to providing LUP advice around major hazard installations.

Major hazard installations are defined as those sites that are required to have Hazardous Substances Consent (DETR, 2000), obtained from the appropriate Hazardous Substances Authority (usually part of the Local Authority). The Hazardous Substances Consent (or Consent for short) defines the quantities of dangerous substances that the site can hold, and may also define the size of the largest storage vessels, the locations of vessels, the locations of areas used to store transportable containers and the maximum temperatures and pressures within storage and process vessels.

Major hazard pipelines (HSE, 1996) are defined in accordance with the kind of material they convey (whether or not it is a ‘dangerous fluid’ under the terms of the legislation). What constitutes a dangerous fluid depends on the pipeline operating conditions as well as the nature of the material conveyed.

The decision-making algorithm used to determine the appropriate advice in a given case is embodied in decision support software called PADHI (Planning Advice for Developments near Hazardous Installations). The PADHI tool is described in a document that may be downloaded from the HSE website (HSE, undated).

2.1 LAND USE PLANNING ZONES

The methodology within PADHI requires that three concentric zones are established around the installation (termed the inner, middle and outer zones, as shown in Figure 1). The outermost edge of the outer zone is the ‘consultation distance’ (CD). The size of these zones can vary significantly from site to site, depending on the type of installation under consideration.

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Site

Inner Zone

Middle Zone

Outer Zone

Consultation Distance

Site

Inner Zone

Middle Zone

Outer Zone

Consultation Distance

Figure 1 Land Use Planning Zones

Similarly, the method by which the zone sizes are established depends on the type of site. For some sites a ‘risk based’ approach is used, whereby the zone boundaries correspond to different values of the risk of an individual receiving a ‘dangerous dose’ or worse.

A dangerous dose is considered to cause all of the following effects to an exposed population:

• severe distress to almost everyone; • a substantial proportion requires medical attention; • some people are seriously injured, requiring prolonged treatment; • any highly susceptible people might be killed.

Exposure to a dangerous dose equates to a probability of fatality of around 1-5% in a typical population.

Hence:

• the boundary between the inner and middle zones corresponds to an individual risk of dangerous dose or worse of 10 chances per million per year (1) (cpm);

• the boundary between the middle and outer zones corresponds to an individual risk of dangerous dose or worse of 1 cpm (2);

• the outer edge of the outer zone (the CD) is set at an individual risk of dangerous dose or worse of 0.3 cpm (3) .

(1) This may also be written as either 1 in 100,000 chances per year, or 1 x 10-5 chances per year. (2) This may also be written as either 1 in 1,000,000 chances per year, or 1 x 10-6 chances per year. (3) This may also be written as either 3 in 10,000,000 chances per year, or 3 x 10-7 chances per year.

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In general, a ‘risk based’ approach is used when the site in question stores or processes toxic substances such as chlorine.

For other sites (typically those handling flammable substances) a ‘protection based’ approach is used. In most cases the protection based approach involves considering the consequences of a selected event (whereas a risk based approach considers both the consequences and likelihood of a range of events). Zone boundaries are set at the range to different levels of harm that would be expected to result from the event:

• the boundary between the inner and middle zones is usually set at the range at which members of a typical population could be subjected to a level of harm corresponding to a significant likelihood of death;

• the boundary between the middle and outer zones is usually set at the range at which a typical, exposed population could experience a dangerous dose;

• the outermost edge of the outer zone is usually set at the range at which a sensitive or vulnerable population could experience a dangerous dose.

2.2 DEVELOPMENT TYPES AND HSE’S ADVICE

Proposed developments are assigned to one of four sensitivity levels, as shown in Table 1. More detailed definitions are provided in the PADHI document.

Table 1 Development Sensitivity Levels

Level Description 1 Based on normal working population 2 Based on the general public – at home and involved in normal activities 3 Based on vulnerable members of the public (children, those with mobility

difficulties or those unable to recognise physical danger) 4 Large examples of Level 3 and large outdoor examples of Level 2.

In each case there are some ‘exclusions’. For example, small housing developments of 1-2 dwellings are ‘excluded’ from Level 2 and placed into Level 1.

For a given development proposal, advice is then generated by essentially using the decision matrix shown in Table 2.

Table 2 Decision Matrix

Sensitivity Level Inner Zone Middle Zone Outer Zone 1 DAA DAA DAA 2 AA DAA DAA 3 AA AA DAA 4 AA AA AA AA: Advise against DAA: Don’t advise against

It should be noted that HSE’s role in the planning process is advisory. The decision as to whether a proposed development receives planning permission rests with the local authority,

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taking into account the advice supplied by HSE. The local authority has to weigh in the balance all of the factors relating to a proposed development (economic, social, environmental, safety) in reaching its decision.

However, HSE has the option to have an application ‘called-in’ for determination by the Secretary of State where it believes that the risks are substantial and the local authority has not given due weight to its advice in coming to their decision.

The following factors would favour calling in the application:

• Any proposals for significant residential development or development for vulnerable populations in the inner zone;

• Proposals where the risk of death exceeds the tolerability limit for a member of the public of 1 x 10-4 per year (HSE, 2001);

• Proposals where there are substantial numbers of people exposed to the risk, giving rise to a high degree of societal concern;

• Proposals where the endangered population is particularly sensitive, (e.g., the development is a hospital, school or old people’s home);

• Whether there have been previous call-ins in similar circumstances; • Whether there are issues of national concern as opposed to merely of local importance;

or, • Whether there is clear evidence that the case concerned is being used to challenge

HSE’s risk criteria for land-use planning and failure to meet that challenge would damage HSE’s credibility; or where a decision against HSE’s advice could, by precedent, set aside parts of the relevant legislation.

For the purposes of this paper, Sensitivity Level 1 developments are of particular interest, since under the current system they would not be advised against even if they were at a location adjacent to a major hazard site boundary (see Table 2 above). Further details of the definition of Sensitivity Level 1 developments have been extracted from the PADHI document and are displayed in Table 3. Those development types which are assigned to Level 1 as a result of being excluded from other Levels are shown in Table 4.

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Table 3 Sensitivity Level 1 Developments

Reference Examples Development Detail and Size Justification DT1.1 Workplaces Offices, factories, warehouses, haulage

depots, farm buildings, non-retail markets, builder’s yards.

Workplaces (predominantly non-retail), providing for less than 100 occupants in each building and less than 3 occupied storeys – Level 1

Places where the occupants will be fit and healthy, and could be organised easily for emergency action. Members of the public will not be present or will be present in very small numbers and for a short time.

EXCLUSIONS DT1.1 x1

DT1.1 x2

DT1.2 Parking Areas

Sheltered workshops, Remploy

Car parks, truck parks, lock-up garages.

DT1.1 x1 Workplaces (predominantly non-retail) providing for 100 or more occupants in any building or 3 or more occupied storeys in height - Level 2 (except where the development is at the major hazard site itself, where it remains Level 1). DT1.1 x2 Workplaces (predominantly non-retail) specifically for people with disabilities - Level 3.

Parking areas with no other associated facilities (other than toilets) – Level 1 EXCLUSIONS

Substantial increase in numbers at risk with no direct benefit from exposure to the risk.

Those at risk may be especially vulnerable to injury from hazardous events and / or they may not be able to be organised easily for emergency action.

DT1.2 x1 Car parks with picnic areas, or at a retail or leisure development, or serving a park and ride interchange.

DT1.2 x1 Where parking areas are associated with other facilities and developments the sensitivity level and the decision will be based on the facility or development.

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Table 4 Sensitivity Level 1 Developments - Exclusions from Other Levels

Reference Examples Development Detail and Size Justification DT2.1 x1 (Exclusion from DT2.1, Infill, backland development. Developments of 1 or 2 dwelling Minimal increase in numbers at risk.

Housing) units - Level 1.

DT2.2 x1 (Exclusion from DT2.2, Smaller - guest houses, hostels, youth Accommodation of less than 10 beds Minimal increase in numbers at risk.

Hotel / Hostel / Holiday hostels, holiday homes, halls of or 3 caravan / tent pitches - Level 1 Accommodation) residence, dormitories, holiday

caravan sites, camping sites. DT2.3 x1 (Exclusion from DT2.3, Estate roads, access roads. Single carriageway roads – Level 1 Minimal numbers present and mostly Transport Links) a small period of time exposed to

risk. Associated with other development.

Any railway or tram track. Railways – Level 1 Transient population, small period of time exposed to risk. Periods of time with no population present.

DT2.4 x1 (Exclusion from DT2.4, Development with less than 250 m2 Minimal increase in numbers at risk. Indoor Use by Public) total floor space – Level 1

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3 REQUIREMENT FOR REVIEW OF CURRENT ARRANGEMENTS

The requirement for review of the current arrangements arises from the experience of the Buncefield incident. As a result of the MIIB investigations, it is known that:

• a storage tank was filled to overflowing with petrol; • as the petrol overflowed from the tank a substantial vapour cloud was generated; • the vapour cloud spread over parts of the site and to areas beyond the site boundary; • the vapour cloud was ignited, resulting in a vapour cloud explosion (VCE); and, • the VCE caused extensive damage to buildings, particularly those close to the site of the

explosion.

Flammable vapour will burn if it is mixed with sufficient air and ignited. Current thinking is that:

• a fuel-air cloud that burns in the open (i.e. in the absence of any confining structures such as walls or roofs) will burn relatively slowly and generate little if any blast pressure; and,

• in order to generate damaging levels of blast pressure, the fuel-air cloud needs to be at least partially confined (i.e. located within walls and/or a roof) or be located within a congested region (i.e. engulfing obstacles such as pipes, steel frames, vessels etc.).

It is also known that ignition of a fuel-air cloud within a small confined volume can produce an explosion which propagates into that (larger) part of the cloud which is outside the confined volume. This is termed ‘bang box’ ignition.

It is also important to note that the characteristics of the blast produced by a VCE differ somewhat from those of the blast produced by a ‘conventional’ explosive such as TNT.

At present it is not clear why the vapour cloud exploded with such force. Although accidents involving VCEs have occurred before and the VCE phenomenon has been the subject of much scientific investigation, an explanation for the strength of the VCE experienced at Buncefield is currently lacking.

At present HSE performs protection based assessments of sites like that at Buncefield (storage facilities for petroleum products). This assessment involves considering the potential for a VCE. However, on the basis of current scientific understanding of the way in which VCEs occur, the potential for a VCE at a site like Buncefield would be limited to those parts of the facility that provided sufficient confinement or congestion to generate a VCE, such as the tanker loading rack, giving rise to relatively small hazard ranges. The protection based assessment would therefore be likely to be based on other hazards, typically large pool fires.

It seems possible that the incident at Buncefield may alter current scientific understanding of VCE mechanisms. This in turn may cause HSE (and risk assessment practitioners generally) to re-think their approach to the assessment of sites storing large quantities of flammable

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substances. However, a detailed understanding of events at Buncefield is at least some months (and possibly, if further experimental investigations are required, some years) away.

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4 OBJECTIVE OF REVISED ARRANGEMENTS

The specific objectives of the proposed revised arrangements are to:

• establish LUP zone boundaries that take into account observations arising from the Buncefield incident; and,

• provide a decision making framework for use with the revised LUP zones that takes into account the particular nature of the VCE hazard.

The proposed arrangements are protection based. The objective of this and other protection based approaches is to:

“achieve a separation between developments and the site which provides a very high degree of protection against the more likely smaller events, whilst also giving very worthwhile (sometimes almost total) protection against unlikely but foreseeable larger-scale events.” (HSE, 1989).

It is not the objective of the proposed arrangements to provide complete protection for future developments from damage, or for their occupants from harm. Neither is it the objective of the proposed arrangements to suggest what should be done about existing land use around affected sites.

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5 OPTIONS FOR REVISED LUP ARRANGEMENTS

The principal features of the system used by HSE for providing LUP advice are:

• The zones around the site; • The development categories; and, • The decision matrix.

Therefore revised arrangements could involve alterations to one or more of these features.

An initial list of options was developed by HSE and presented to ERM for consideration. These options are listed in Table 5, together with the author’s comments in each case.

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Table 5 Comments on Options for Revision of LUP Arrangements

Option 1. No change to existing planning zones and CDs [consultation distances]. Use existing LUP matrix for LUP advice.

2. Change LUP zones (for Buncefield or similar sites) plus existing LUP matrix.

2.1(a), (b) Change LUP zones (for Buncefield or similar sites) using VCE calculated on foreseeable loss of containment (LOC) amount, plus existing LUP matrix. Either (a) base upon existing methodology or (b) base upon varying stepped values of assumed congestion up to a maximum value.

ERM Comment Given the potential number of casualties (had the accident occurred when nearby buildings were occupied) and the level of public concern, this is not considered to be a viable option. A revision to the way the LUP zones are set is probably necessary in view of the nature of the incident (i.e., a VCE not a pool fire). However, if this were used in conjunction with the existing matrix, Sensitivity Level 1 developments would still ‘not be advised against’ within the Inner Zone, right up to the site boundary. Hence in some ways this option does not take into account the experience at Buncefield (i.e., the extensive damage to commercial / office buildings and potential numbers of casualties). Therefore the author considers that a revision to the matrix (or at least Sensitivity Level definitions) is required, as well as revision of the zone boundaries. A fuller understanding of the event sequence and mechanism of the Buncefield explosion may alter views about what constitutes a ‘foreseeable’ event. It is understood that, based on current views about what is foreseeable, HSE already conducts assessments of potential VCE events at such establishments. See also comments on Option 2 above.

2.1 (c) Change LUP zones (for Buncefield or similar sites), plus existing LUP matrix. Base upon (c) observed overpressure at Buncefield.

This option has some advantages in that it is based on experience as opposed to conjecture about the event sequence and mechanism of the VCE. However, estimates of overpressure obtained from observed damage are subject to uncertainty. This could be avoided by using distances to observed damage levels to set zone boundaries rather than distances to estimated overpressure levels. See also comments on Option 2 above.

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Option ERM Comment 2.2(a), (b) Change LUP zones (for Buncefield or similar sites) using VCE calculated on extremely large loss of containment (LOC) amount, plus existing LUP matrix. Either (a) base upon existing methodology or (b) base upon varying stepped values of assumed congestion up to a maximum value.

Current understanding of VCE mechanisms indicates that, in the case of a very large release, the magnitude of the explosion becomes limited by the size of the confined / congested volume available rather than by the size of the cloud. At a site similar to Buncefield the available confined / congested volumes are typically small (e.g. loading racks) and therefore this approach is likely to give the same results as 2.1. See also comments on Option 2 above.

2.2 (c) Change LUP zones (for Buncefield or similar sites), plus existing It is not clear how this option differs from 2.1 (c). See comments on Option LUP matrix. Base upon (c) observed overpressure at Buncefield. 2.1 (c) above. 3. Change LUP zones [in one of the ways described in Option 2] plus new A combination of revised zones and a revised decision framework is, in the LUP matrix. New LUP matrix could take into account propensity to author’s view the most promising way forward. It may not be necessary to damage. Develop advice DAA/AA [Don’t Advise Against / Advise revise the decision matrix, one possible solution may be to alter the Against] based upon overpressure and building design. sensitivity level definitions to reflect building vulnerability to blast. 3.1 and 3.2 as 2.1 and 2.2 [but with revised LUP matrix]. See comments on 2.1, 2.2 and 3 above. 4. No change to existing policy, but review all planning applications on a A basis for decision making would still need to be established, even if it case by case basis [either] (a) around Buncefield or (b) elsewhere was only available within HSE. This would require development of one of

the other options. 5. Moratorium on all planning applications within (a) existing CDs; (b) Until further information becomes available, it is not clear whether the proposed new CD based on Option 2 above; or (c) inner zone. existing zones are large enough for options 5 (a) or 5 (c) (i.e., it is possible

that zones should be larger than they are at present). Although a precautionary approach is considered to be appropriate under the circumstances, a complete moratorium seems indiscriminate and may result in further distress among people living or working in the affected zones. It is the author’s view that a moratorium should not be dismissed as a possibility, but should only be considered if a workable, more refined approach cannot be developed in the required time scales.

6. Create a ‘cordon sanitaire’ around Buncefield and all other sites. This does not seem to be a likely way forward in the short term. 7 (a) For the above calculations [Option 2 or 3] change zones for Buncefield At present there does not seem to be a good reason for considering only Buncefield alone. It is understood that there have been accidents in France

and the USA which bear some similarities to Buncefield, so there is evidence to indicate that the circumstances are not unique.

13

Option ERM Comment 7 (b) For the above calculations [Option 2 or 3] change zones for all 97 oil This seems a more logical approach than 7 (a). storage sites 7 (c) For the above calculations [Option 2 or 3] change zones for some of This is viewed as the favoured approach, although a firm basis for the 97 based upon gasoline for sites where tanks are floating roof and filled identifying which sites should be included needs to be developed. by pipeline 7 (d) For the above calculations [Option 2 or 3] change zones for all sites If a VCE is foreseeable on the basis of current understanding, then HSE will where there is a foreseeable risk of VCE. already have taken this into account. However, it is possible that as the

investigation proceeds the view of what is ‘foreseeable’ will change, requiring a broader re-evaluation of the approach taken with VCE hazards. It is recommended that this is considered further as more information becomes available.

14

Overall, it was judged that any revised approach should have regard for the current state of knowledge regarding events at Buncefield, and should be somewhat precautionary in nature. In summary, it was recommended that consideration be given to amendment of both the zones and the development sensitivity level definitions.

5.1 CHANGES TO LUP ZONES

It was decided that observations of the damage incurred at Buncefield could be used to estimate maximum ranges to damage levels of interest. These distances would then be used to establish LUP zone boundaries. For example, the inner zone distance would correspond to the maximum range to serious structural damage. Establishing zone boundaries on the basis of observed damage rather than an estimate of the overpressure required to cause the observed level of damage avoids the uncertainty inherent in the overpressure estimate.

An analytical approach to establishing LUP zones (e.g. by using an explosion model to calculate distances to overpressures of interest) is not considered feasible at present, owing to the lack of understanding of the explosion mechanism involved.

5.2 CHANGES TO SENSITIVITY LEVEL DEFINITIONS

In addition, the definition of Sensitivity Level 1 (S1) developments was revisited to ensure that the nature of the vapour cloud explosion hazard and the effect of such events on building occupants were addressed adequately.

15

6 DEVELOPMENT OF PROPOSALS FOR REVISED ARRANGEMENTS

The proposed revised arrangements have been developed by:

• Reviewing published HSE research on the effects of explosions (Jeffries et al., 1997; Galbraith, 1998), (see Appendix 1);

• Considering the levels of damage to buildings observed around the Buncefield site (see Appendix 2);

• Revisiting the justifications underlying the Sensitivity Level definitions for proposed developments in the light of the first two activities.

The review of published HSE research found that a model for predicting the effects of blast from VCEs on buildings and their occupants (Jeffries et al., 1997) contained flaws which raised questions over the validity of the model results. Further development of the model would be necessary to rectify these problems.

6.1 REVISION OF LUP ZONE BOUNDARIES

Some limited but useful data are available which correlate levels of building damage to the harm suffered by their occupants (Galbraith, 1998). These data result from observations of bomb damage sustained during the Second World War.

In conjunction with the observations of damage to buildings, the data have been used to form a judgement concerning the likelihood of harm (in broad terms) to the occupants of different buildings. Damaged buildings were assigned to one of four harm categories: high, medium, low and minimal. The first three of these categories correspond to the three harm levels used when performing a protection based assessment (see Section 2.1). The ‘minimal’ category indicates that the potential for harm to occupants arising from damage to the building was such that it would not be of interest for the purposes of setting LUP zone boundaries.

The distances to buildings in the different harm categories were measured and used to establish zone boundaries. This resulted in the proposed zone boundary distances displayed in Table 6. The process is described in detail in Appendix 3.

Table 6 Proposed Zone Boundaries

Zone Distance (m) Inner 250 Middle 300 Outer 400

16

6.2 REVISION OF SENSITIVITY LEVEL DEFINITIONS

The Buncefield explosion and subsequent fires resulted in significant damage to property; particularly to those buildings situated relatively close to the installation (see Appendix 2). For the Northgate and Fuji buildings, from the information available it seems likely that, had people been present in those parts of these buildings closest to the site, they would have been exposed to a level of harm presenting a significant likelihood of death (see Appendix 3).

These observations have prompted the author to review the HSE definitions of Sensitivity Level 1 developments, since such developments would not be advised against anywhere within the consultation distance, even within the inner zone (see Table 2). Hence such developments could, under existing arrangements, be placed at locations where levels of individual risk were relatively high.

Essentially Sensitivity Level 1 developments have been defined as:

• small examples of housing, holiday / hostel and retail / leisure developments (see Table 4); and,

• office, factories and workplaces for less than 100 occupants and less than 3 stories in height (see Table 3).

The justifications for placing these types of development into Sensitivity Level 1 are discussed below.

Throughout these discussions, it is important to note that the HSE calculates risk in terms of the individual risk of experiencing a ‘dangerous dose or worse’, as opposed to the individual risk of fatality (see Section 2.1). Exposure to a dangerous dose corresponds to approximately a 1-5% probability of fatality to a typical cross-section of the population (with only the most vulnerable or sensitive individuals becoming fatalities). However, the proportion of ‘or worse’ within the risk of dangerous dose or worse varies as a function of distance from an installation and with the hazards presented by the installation.

For most types of hazard, as the site of interest is approached the proportion of ‘or worse’ (e.g., fatality) within the risk of dangerous dose or worse is increased. Also, the proportion of ‘or worse’ tends to be higher with fire and explosion hazards than with most toxic hazards. Indeed, for some types of fire or explosion event (including a VCE like that experienced at Buncefield), in the near field the risk of dangerous dose or worse is almost entirely a risk of fatality.

6.2.1 Small housing, hotel / hostel and retail / leisure developments

Several smaller developments of various types are assigned to Sensitivity Level 1 as a result of an ‘exclusion’ from another Level (see Table 4). These include:

• housing developments for 1 or 2 dwellings; • holiday / hostel accommodation of less than 10 beds or 3 caravan / tent pitches; and, • retail / leisure development with less than 250 m2 total floor space.

17

For each of these development types, the justification given within the PADHI document (HSE, -) is that there is ‘minimal increase in numbers at risk’. A more detailed discussion of the justification is presented in HSE’s risk criteria document for land use planning (HSE, 1989). This document provides a second reason for not advising against such developments:

“the ‘dangerous dose’ would only be fatal for a small fraction of the population, and a fraction of the population of two houses is probably zero.” (HSE, 1989; para. 85).

Although this statement relates to small housing developments, the document makes it clear that holiday / hostel accommodation is placed in the same category as housing (HSE, 1989; para. 81); and retail / leisure development is assumed to be “similar in significance” to housing (HSE, 1989; para. 82).

These justifications relate to the increment of societal risk associated with a proposed development (the case societal risk). The first relates to the number of people exposed to the risk, the second to the numbers of people who might become fatalities if exposed to a dangerous dose.

For the first of the justifications given (‘minimal increase in numbers at risk’) it appears that the low case societal risk associated with such developments has been given greater weight than the relatively high individual risk to which people could be exposed. This arises from a tension between two of the stated principles of HSE’s involvement in land-use planning, that:

“The risk from a hazardous installation to an individual employee or member of the public should not be significant when compared with other risks to which he is exposed in everyday life.” (Advisory Committee on Major Hazards, 1984) para. 21;

and:

“The separation of a hazard from a built-up area need not mean… that the intervening land is completely sterilised or available only for agricultural purposes. Depending on the degree of hazard, it may be possible for it to be allocated for other purposes involving low population densities, including some industrial developments.” (Advisory Committee on Major Hazards, 1984), para. 84.

Under the current arrangements, the second of these principles overrides the first for some of those developments falling into Sensitivity Level 1. However, for a site with the potential for a VCE like that experienced at Buncefield, the risk of ‘dangerous dose or worse’ close to the site is likely to be almost entirely a risk of fatality. In view of this, it is proposed that for certain developments currently placed within Sensitivity Level 1, the balance between the two principles stated above is shifted in favour of the first, and that these developments should be assigned to Sensitivity Level 2.

The second justification is essentially that, in a small number of exposed people, it is probable that none of them would be particularly sensitive or vulnerable to the hazard in question. Therefore, if this group of people was exposed to a dangerous dose, it is unlikely that any fatalities would result. However, this argument does not consider the proportion of ‘or worse’ within the ‘dangerous dose or worse’. As discussed above, for a VCE like that experienced at

18

Buncefield, the ‘or worse’ proportion is likely to be high close to the event. Hence, even amongst a small group of people, some fatalities could result. This supports the proposal that the types of developments in question should be re-assigned to Sensitivity Level 2.

This issues discussed in this Section have broader implications and are not specifically related to the Buncefield accident or the VCE hazard. However, it is considered prudent to address them in the context of this study, in view of the significant likelihood of fatality to which people close to sites of interest could be exposed.

6.2.2 Workplaces

The first part of the justification given for assigning workplaces to Sensitivity Level 1 is that these are ‘places where the occupants will be fit and healthy, and could be organised easily for emergency action’ (see Table 3).

The first part of the justification (‘occupants fit and healthy’) appears to suggest that amongst a group of workers, it is likely that the proportion that could be considered particularly sensitive or vulnerable would be lower than in the population at large. Therefore, if this group of workers was exposed to a dangerous dose, the resulting number of fatalities would probably be lower than for a group of the same size but representing a ‘typical’ cross-section of the general population.

However, as with one of the justifications discussed in the previous Section, this argument does not consider the proportion of ‘or worse’ within the ‘dangerous dose or worse’. As discussed above, for a VCE like that experienced at Buncefield, the ‘or worse’ proportion is likely to be high close to the event. Hence, even amongst a ‘fit and healthy’ group of people, some fatalities could result.

The second part of the justification appears to be that the risk to people in a workplace would be significantly reduced as a result of taking emergency action. This assumes that:

• effective emergency action (such as evacuation or sheltering) is possible; and, • there is sufficient time for this action to be taken.

With regard to the first of these points it is not clear what would constitute effective emergency action for occupants of workplaces close to a site presenting a VCE hazard. Evacuation of building occupants could place them in the flammable cloud. However, remaining within a building could place the occupants at greater risk of injury from blast effects.

Secondly, even if some kind of emergency action was possible, a VCE could occur rapidly, with little or no opportunity for raising the alarm.

In view of this, it is recommended that consideration is given to alteration of the definition of Sensitivity Level 1 developments within the revised arrangements. A more detailed discussion of the case societal risk aspects of workplace developments is presented in Appendix 4.

19

6.2.3 Summary of Recommendations

The recommended alterations to the Sensitivity Level definitions are as follows:

• all workplaces that are routinely occupied for a significant proportion of the time (i.e. – offices and factories), regardless of size, are re-assigned to Level 2;

• workplaces or areas that are visited intermittently (warehouses, timber yards, outdoor storage areas, haulage depots, farm buildings) with no associated office facilities and car parks with no associated amenities remain in Level 1;

• housing developments of 1 or 2 dwelling units are re-assigned to Level 2; • smaller hotel / holiday / hostel accommodation is assigned to Level 2; and, • retail development with less than 250 m2 floor space is assigned to Level 2.

6.3 OPTIONS

Since the proposed revised zone boundaries are considerably larger than those normally encountered for those sites of interest (see Table 6), the view could be taken that it would be sufficiently precautionary to change the zone boundaries without changing the Sensitivity Levels. This results in two options for revised arrangements:

• Option A: Increase the size of the LUP zones only; or, • Option B: Increase the size of the LUP zones and revise the development sensitivity

levels.

6.4 APPLICATION

It is recommended that the proposed arrangements are applied to those sites which are similar to Buncefield in a number of important respects. These similarities would indicate that on the basis of what is known at present, the site has the potential to give rise to a VCE.

If implemented, it is recommended that the proposed arrangements are applied to sites with the following characteristics:

• the site is classed as either ‘upper tier’ or ‘lower tier’ under the Control of major

Accident Hazards Regulations 1999 (the COMAH Regulations);

• the site stores petroleum in vertical, cylindrical, non-refrigerated above-ground storage tanks with side walls greater than 5 m in height; and,

• the filling rate of the storage tanks is greater than 100 m3 / hour.

These criteria align with those used by the Buncefield Standards Task Group, a joint COMAH Competent Authority and Industry committee (HSE, 2006).

20

7 IMPACT OF THE PROPOSED ARRANGEMENTS

The impact of the proposed options has been illustrated by considering a series of hypothetical developments at different locations around a hypothetical site. Under the current system the hypothetical site has the inner, middle and outer zone boundaries set at distances of 120 m, 135 m and 185 m respectively (these distances correspond to those currently set for the Buncefield site). The proposed revisions to the system would increase these distances to those presented in Table 6. The selected locations are displayed in Figure 2. With regard to these locations, it should be noted that:

• Location 1 is within the current inner zone; • Location 2 is within the current middle zone; • Location 3 is within the current outer zone; and, • Locations 4, 5 and 6 are all outside the current consultation distance.

Although the current middle zone is quite ‘narrow’, it has been assumed for the purposes of the illustrations that Location 2 is able to accommodate the hypothetical developments considered (1).

Different types of development have been represented by symbols. A key to the symbols used in the illustrations is presented in Figure 3, Figure 4 and Figure 5.

The illustrations are provided in the following figures:

• Figure 6 Comparison of Existing and Revised LUP Zones; • Figure 7 Illustration 1: Current Situation, Inner Zone; • Figure 8 Illustration 2: Current Situation, Middle Zone; • Figure 9 Illustration 3: Current Situation, Outer Zone; • Figure 10 Illustration 4: Current Situation, Beyond CD; • Figure 11 Illustration 5: Option A (Revised Zones Only), Inner Zone; • Figure 12 Illustration 6: Option A (Revised Zones Only), Middle Zone; • Figure 13 Illustration 7: Option A (Revised Zones Only), Outer Zone; • Figure 14 Illustration 8: Option B (Revised Zones and Sensitivity Levels), Inner Zone; • Figure 15 Illustration 9: Option B (Revised Zones and Sensitivity Levels), Middle

Zone; and, • Figure 16 Illustration 10: Option B (Revised Zones and Sensitivity Levels), Outer Zone.

The illustrations are also summarised in Table 7, where differences with the current system are shown by highlighted cells.

(1) There are additional rules within the current policy to address developments which straddle zone boundaries.

21

1

2

3

45

6Key Inner Zone Middle Zone Outer Zone

Site

1

2

3

4 5

6 KeyInner ZoneMiddle ZoneOuter Zone

KeyInner ZoneMiddle ZoneOuter Zone

Site

Figure 2 Location of Hypothetical Developments

22

SymboSymboll DescriptionDescription SymbolSymbol DescriptionDescription

Factory, providing for less than 100Factory, providing for less than 100occupants in each buildoccupants in each buildiing and less thanng and less than3 occupied storeys.3 occupied storeys.

Factory, providing for more than 100Factory, providing for more than 100 occupants in each building or more than 3occupants in each building or more than 3occupoccupiied storeys.ed storeys.

Offices, provOffices, proviiddiing for less than 100ng for less than 100 occupants in each buildoccupants in each buildiing and less thanng and less than3 occupied storeys.3 occupied storeys.

Offices, provOffices, proviiddiing for more than 100ng for more than 100occupants in each building or more than 3occupants in each building or more than 3occupoccupiied storeys.ed storeys.

Housing: DeveHousing: Devellopments of 1 or 2opments of 1 or 2 Housing: developments of more thanHousing: developments of more thandwelling unitsdwelling units 1 or 2 un1 or 2 uniits, up to andts, up to and iincncllududiing 30ng 30

dwedwelllliing unng uniits and at a density of nots and at a density of no more than 40 per hectare.more than 40 per hectare.

Developments for use by the generalDevelopments for use by the general Developments for use by the generalDevelopments for use by the general public: Development wpublic: Development wiith less thanth less than public where total floor space is frompublic where total floor space is from250 m2 total floor space250 m2 total floor space 250 m2 up to 5000 m2250 m2 up to 5000 m2..

Figure 3 Key to Symbols (Part 1)

23

24

Symbol SymbolDescription Description

Institutional: Hospital, where the site being developed is less than 0.25 hectares.

Institutional: Hospital, where the site being developed is larger than 0.25 hectares.

Institutional: School (not 24 hour care), where the site being developed is less than 1.4 hectares.

Developments for use by the general public where total floor space is greater than 5000 m2.

Housing: developments of more than 30 dwelling units or at a density of more than 40 per hectare.

Developments for use by the general public Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time

Workplace: Warehousing with no associated offices / factory.

Workplace: Outdoor storage with no associated offices / factory.

Symbol SymbolDescription Description

Institutional: Hospital, where the site being developed is less than 0.25 hectares.

Institutional: Hospital, where the site being developed is larger than 0.25 hectares.


Developments for use by the general public where total floor space is greater than 5000 m2.


Developments for use by the general public Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time




SymboSymboll DescrDescriiptptiionon SymboSymboll DescriptionDescription

Parking areas wParking areas wiith no otherth no other Workplace: Farm buildWorkplace: Farm buildiings with nongs with no associated facilitiesassociated facilities ((other thanother than associated officesassociated offices // factory.factory.totoiillets).ets).

Factory, regardless of number ofFactory, regardless of number of Offices, regardOffices, regardlless of number ofess of number ofoccupants in each buildoccupants in each buildiing and numberng and number occupants in each buildoccupants in each buildiing andng andof occupied storeys.of occupied storeys. number of occupied storeys.number of occupied storeys.

Housing: developments of up to andHousing: developments of up to andincluding 30 dwelling unincluding 30 dwelling uniits and at ats and at adensity of no more than 40 perdensity of no more than 40 per hectare. Includes small developmentshectare. Includes small developmentsof 1-2 unof 1-2 uniitsts

Developments for use by the generalDevelopments for use by the general public all developments where totalpublic all developments where totalfflloor space is up to 5000 m2. Includesoor space is up to 5000 m2. Includesdevelopments wdevelopments wiithth lless than 250 m2ess than 250 m2fflloor space.oor space.


25

SiteSite

Existing Zones Revised Zones

SiteSite

Existing Zones Revised Zones

Figure 6 Comparison of Existing and Revised LUP Zones

26

27

9 8

88

Current Inner Zone

Sensitivity Level 1 Sensitivity Level 2



Site

9 8

88

Current Inner Zone









Site

Figure 7 Illustration 1: Current Situation, Inner Zone

28

9

88

Current Middle Zone



9


Site

9

88

Current Middle Zone







9



Site

Figure 8 Illustration 2: Current Situation, Middle Zone

29

9 9

8

Current Outer Zone

9




Site

9 9

8

Current Outer Zone

9









Site

Figure 9 Illustration 3: Current Situation, Outer Zone

Beyond the Current CDBeyond the Current CDNo consultation with HSE requiredNo consultation with HSE required

Key Inner Zone Middle Zone Outer Zone

Site



Site

Figure 10 Illustration 4: Current Situation, Beyond CD

30

31

9 8

88

Proposed Inner ZoneNo change to Sensitivity Levels






Site

9 8

88

Proposed Inner ZoneNo change to Sensitivity Levels















Site

Figure 11 Illustration 5: Option A (Revised Zones Only), Inner Zone

32

9

8

9

8

Proposed Middle ZoneNo change to Sensitivity Levels




Site

9

8

9

8

Proposed Middle ZoneNo change to Sensitivity Levels









Site

Figure 12 Illustration 6: Option A (Revised Zones Only), Middle Zone

33

9

8

Proposed Outer ZoneNo change to Sensitivity Levels

9

9




Site

9

8

Proposed Outer ZoneNo change to Sensitivity Levels

9

9









Site

Figure 13 Illustration 7: Option A (Revised Zones Only), Outer Zone

34

9 8

88

Proposed Inner ZoneRevised Sensitivity Levels




Site

9 8

88

Proposed Inner ZoneRevised Sensitivity Levels







Site

Figure 14 Illustration 8: Option B (Revised Zones and Sensitivity Levels), Inner Zone

35

9

8

9

8

Proposed Middle ZoneRevised Sensitivity Levels




Site

9

8

9

8

Proposed Middle ZoneRevised Sensitivity Levels







Site

Figure 15 Illustration 9: Option B (Revised Zones and Sensitivity Levels), Middle Zone

36

9

8

Proposed Outer ZoneRevised Sensitivity Levels

9

9




Site

9

8

Proposed Outer ZoneRevised Sensitivity Levels

9

9





Site

Figure 16 Illustration 10: Option B (Revised Zones and Sensitivity Levels), Outer Zone

Table 7 Summary of Illustrations

Location Current Development Description Current Current Proposed Option A Option B Option B Zone Sensitivity Advice Zone Advice Sensitivity Advice

Level Level 1 1 9 9 2 8

Offices 1 9 9 2 8

1 9 9 2 8 for use by the :

21 9 9 2 8

Inner Factory, providing for less than 100 occupants in each building and less than 3 occupied storeys.

Inner

, providing for less than 100 occupants in each building and less than 3 occupied storeys.

Inner

Housing: Developments of 1 or 2 dwelling units Inner Developments general publicDevelopment with less than 250 m total floor space

Inner

Workplace: Warehousing with no associated offices / 1 9 Inner 9 1 9 factory. Workplace: Outdoor storage with no associated offices / 1 9 Inner 9 1 9 factory. Workplace: Farm buildings with no associated offices / 1 9 Inner 9 1 9 factory. Parking areas with no other associated facilities (other 1 9 Inner 9 1 9 than toilets). All other developments in Sensitivity Levels 2, 3 and 4 2, 3, 4 8 Inner 8 2, 3, 4 8

2 1 9 9 2 8

Offices 1 9 9 2 8


21 9 9 2 8

Middle Factory, providing for less than 100 occupants in each building and less than 3 occupied storeys.

Inner


Inner


Inner

Workplace: Warehousing with no associated offices / 1 9 Inner 9 1 factory.

37

9

Location Current Zone

Development Description Current Sensitivity

Level

Current Advice

Proposed Zone

Option A Advice

Option B Sensitivity

Level

Option B Advice


1 9 Inner 9 1 9

Workplace: Farm buildings with no associated offices / factory.

1 9 Inner 9 1 9

Parking areas with no other associated facilities (other than toilets).

1 9 Inner 9 1 9

2 9 8 2 8

Offices 2 9 8 2 8

2 9 8 2 8

2 2 . 2 9 8 2 8

Factory, providing for more than 100 occupants in each building or more than 3 occupied storeys.

Inner

, providing for more than 100 occupants in each building or more than 3 occupied storeys.

Inner

Housing: developments of more than 1 or 2 units, up to and including 30 dwelling units and at a density of no more than 40 per hectare.

Inner

Developments for use by the general public where total floor space is from 250 m up to 5000 m

Inner

All other developments in Sensitivity Levels 3 and 4 3, 4 8 Inner 8 3, 4 3 1 9 9 2 8

Offices 1 9 9 2 8


21 9 9 2 8

Outer Factory, providing for less than 100 occupants in each building and less than 3 occupied storeys.

Inner


Inner


Inner


1 9 Inner 9 1 9


1 9 Inner 9 1 9


1 9 Inner 9 1 9

38

8


Level Level Parking areas with no other associated facilities (other 1 9 Inner 9 1 9 than toilets).

2 9 8 2 8

Offices 2 9 8 2 8

2 9 8 2 8

2 2 . 2 9 8 2 8

Institutional 3 9 8 3 8

Institutional ) 3 9 8 3 8

3 9 8 3 8

2 . 3 9 8 3 8


Inner

, providing for more than 100 occupants in each building or more than 3 occupied storeys.

Inner


Inner

Developments for use by the general public where total floor space is from 250 m up to 5000 m

Inner

: Hospital, where the site being developed is less than 0.25 hectares.

Inner

: School (not 24 hour care , where the site being developed is less than 1.4 hectares.

Inner


Inner

Developments for use by the general public where total floor space is greater than 5000 m

Inner

Institutional: Hospital, where the site being developed is 4 8 Inner 8 4 8 larger than 0.25 hectares. Developments for use by the general public 4 8 Inner 8 4 8 Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time.

4CD

1 Not 9 2 8

Offices 1 Not 9 2 8

Beyond Factory, providing for less than 100 occupants in each building and less than 3 occupied storeys. Applicable

Inner

, providing for less than 100 occupants in each building and less than 3 occupied storeys. Applicable

Inner

39


Level Level 4

CD 1 9 2 8

for use by the : 2

1 Not 9 2 8

Beyond Housing: Developments of 1 or 2 dwelling units Not Applicable

Inner

(contd.) Developments general publicDevelopment with less than 250 m total floor space Applicable

Inner

Workplace: Warehousing with no associated offices / 1 Not Inner 9 1 9 factory. Applicable Workplace: Outdoor storage with no associated offices / 1 Not Inner 9 1 9 factory. Applicable Workplace: Farm buildings with no associated offices / 1 Not Inner 9 1 9 factory. Applicable Parking areas with no other associated facilities (other 1 Not Inner 9 1 9 than toilets). Applicable

2 Not 8 2 8

Offices 2 Not 8 2 8

2 Not 8 2 8

2 2 . 2 Not 8 2 8

Institutional 3 Not 8 3 8

Institutional ) 3 Not 8 3 8

3 Not 8 3 8

2 . 3 Not 8 3 8

Factory, providing for more than 100 occupants in each building or more than 3 occupied storeys. Applicable

Inner

, providing for more than 100 occupants in each building or more than 3 occupied storeys. Applicable

Inner


Applicable Inner

Developments for use by the general public where total floor space is from 250 m up to 5000 m Applicable

Inner

: Hospital, where the site being developed is less than 0.25 hectares. Applicable

Inner

: School (not 24 hour care , where the site being developed is less than 1.4 hectares. Applicable

Inner

Housing: developments of more than 30 dwelling units or at a density of more than 40 per hectare. Applicable

Inner

Developments for use by the general public where total floor space is greater than 5000 m Applicable

Inner

40


Level Level 4

CD Institutional 4 Not 8 4 8

for use by the public 4 Not 8 4 8

Beyond : Hospital, where the site being developed is larger than 0.25 hectares. Applicable

Inner

(contd.) Developments general Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time.

Applicable Inner

5 Beyond Factory, providing for less than 100 occupants in each 1 Not Middle 9 2 9 CD building and less than 3 occupied storeys. Applicable

Offices, providing for less than 100 occupants in each 1 Not Middle 9 2 9 building and less than 3 occupied storeys. Applicable Housing: Developments of 1 or 2 dwelling units 1 Not Middle 9 2 9

Applicable Developments for use by the general public: Development with less than 250 m2 total floor space

1 Not Applicable

Middle 9 2 9

Workplace: Warehousing with no associated offices / 1 Not Middle 9 1 9 factory. Applicable Workplace: Outdoor storage with no associated offices / 1 Not Middle 9 1 9 factory. Applicable Workplace: Farm buildings with no associated offices / 1 Not Middle 9 1 9 factory. Applicable Parking areas with no other associated facilities (other 1 Not Middle 9 1 9 than toilets). Applicable Factory, providing for more than 100 occupants in each 2 Not Middle 9 2 9 building or more than 3 occupied storeys. Applicable Offices, providing for more than 100 occupants in each 2 Not Middle 9 2 9 building or more than 3 occupied storeys. Applicable Housing: developments of more than 1 or 2 units, up to 2 Not Middle 9 2 9 and including 30 dwelling units and at a density of no Applicable more than 40 per hectare.

41


Level Level 5 Beyond

CD Developments for use by the general public where total floor space is from 250 m2 up to 5000 m2 .

2 Not Applicable

Middle 9 2 9


Institutional ) 3 Not 8 3 8

3 Not 8 3 8

2 . 3 Not 8 3 8



(contd.) : Hospital, where the site being developed is less than 0.25 hectares. Applicable

Middle

: School (not 24 hour care , where the site being developed is less than 1.4 hectares. Applicable

Middle

Housing: developments of more than 30 dwelling units or at a density of more than 40 per hectare. Applicable

Middle

Developments for use by the general public where total floor space is greater than 5000 m Applicable

Middle

: Hospital, where the site being developed is larger than 0.25 hectares. Applicable

Middle

Developments general Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time.

Applicable Middle

6 Beyond Factory, providing for less than 100 occupants in each 1 Not Outer 9 2 9 CD building and less than 3 occupied storeys. Applicable

Offices, providing for less than 100 occupants in each 1 Not Outer 9 2 9 building and less than 3 occupied storeys. Applicable Housing: Developments of 1 or 2 dwelling units 1 Not Outer 9 2 9

Applicable Developments for use by the general public: Development with less than 250 m2 total floor space

1 Not Applicable

Outer 9 2 9

Workplace: Warehousing with no associated offices / 1 Not Outer 9 1 9 factory. Applicable Workplace: Outdoor storage with no associated offices / 1 Not Outer 9 1 9 factory. Applicable

42

Location Current Zone

Development Description Current Sensitivity

Level

Current Advice

Proposed Zone

Option A Advice

Option B Sensitivity

Level

Option B Advice

6 Beyond CD


1 Not Applicable

Outer 9 1 9

(contd.) Parking areas with no other associated facilities (other than toilets).

1 Not Applicable

Outer 9 1 9


2 Not Applicable

Outer 9 2 9

Offices, providing for more than 100 occupants in each building or more than 3 occupied storeys. Housing: developments of more than 1 or 2 units, up to and including 30 dwelling units and at a density of no more than 40 per hectare. Developments for use by the general public where total floor space is from 250 m2 up to 5000 m2 . Institutional: Hospital, where the site being developed is less than 0.25 hectares.

2

2

2

3

Not Applicable

Not Applicable

Not Applicable

Not Applicable

Outer

Outer

Outer

Outer

9

9

9

9

2

2

2

3

9

9

9

9


3 Not Applicable

Outer 9 3 9


3 Not Applicable

Outer 9 3 9

Developments for use by the general public where total floor space is greater than 5000 m2 .

3 Not Applicable

Outer 9 3 9



: Hospital, where the site being developed is larger than 0.25 hectares. Applicable

Outer

Developments general Predominantly open-air developments likely to attract the general public in numbers greater than 1000 people at any one time.

Applicable Outer

KEY: 9 Don’t Advise Against; 8 Advise Against; Not Applicable – no requirement to consult HSE

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7.1 SUMMARY OF IMPACTS

In comparison with the current system, the proposed changes will, if implemented, result in:

• significantly larger CDs and zone boundaries for the sites affected (for both Options A and B);

• as a result of the increased area within the CD, a larger number of consultations concerning proposed developments in the vicinity of affected sites (for both Options A and B); and,

• more restrictive advice concerning developments in the inner zone (for Option B).

Furthermore, it is recognised that there may be significant implications in the proposed arrangements for other types of site. These sites include bulk LPG storage, gasholders, other flammable liquid storage and other facilities presenting a hazard with an associated significant likelihood of death in the inner zone (including VCEs and other hazards such as fireballs). This is because the points raised in Section 6.2 concerning possible means of and time available for emergency action are equally applicable to such sites. A review of the implications of the study findings for LUP arrangements applicable to other types of site is recommended.

7.2 ADVANTAGES AND DISADVANTAGES

The advantages and disadvantages of the proposed system are displayed in Table 8.

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Table 8 Advantages and Disadvantages

Advantages Disadvantages Precautionary in the light of current The system relies on interpretation of understanding. damage and historical information, which is

open to debate. In particular, the historical data relate to experience with ‘conventional explosives’ which produce blast with different characteristics to that from a VCE.

Based on accident experience, less The system may not be precautionary enough contentious than using predictive models, (i.e. it is possible that a VCE at another particularly in view of current uncertainties. comparable site could be worse than that at

Buncefield). Provides increased separation for sensitive or normally occupied developments (due to the larger CD), particularly to those in office / factory developments excluded from the inner zone (due to changes in Sensitivity Level definitions).

The change gives rise to inconsistency – those sites affected by the proposed system will use the revised set of Sensitivity Level definitions, other sites will use the current definitions.

Relatively quick and straightforward to The increase in CDs and more restrictive implement. advice may generate an adverse reaction

from local authorities, developers, etc. For those sites affected, it will not be possible to use the existing PADHI software to determine the appropriate advice. This is likely to have resource implications for HSE.

On balance it is considered that the proposed system reflects the best that can be achieved with the time and information available.

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8 SENSITIVITY

In Table 8, it was observed that the proposed system may not be sufficiently precautionary (i.e. that a VCE at another comparable site could be worse than that at Buncefield). In view of this, an investigation of the sensitivity of the size of the boundaries to various factors was undertaken. The factors considered included:

• the rate at which vapour is formed and the conditions under which this occurs (the source term);

• the way in which the cloud moves (the dispersion of the vapour); • the quantity of fuel involved in the explosion (the explosion size); and, • the violence of the explosion (the explosion strength).

8.1 SOURCE TERM

The manner in which vapour was generated during the Buncefield incident is described in the third progress report published by the MIIB (2006c).

In summary, liquid overflowed from the tank through eight vents around the tank roof. This liquid flowed down the surface of the conical roof until it reached the roof edge. At this point the liquid struck a deflector plate (designed to direct firewater onto the tank wall). The deflector plate directed a proportion of the liquid on to the tank wall, but the remainder cascaded over the top of the plate, forming airborne droplets. The proportion of the liquid directed on to the wall flowed downwards until it struck a wind girder running circumferentially around the tank. As the liquid struck the girder a proportion of it was directed away from the tank wall, again forming a shower of droplets. This is illustrated in Figure 17, copied from the third progress report (MIIB, 2006c).

The formation of showers of droplets enhanced the evaporation of the liquid fuel, forming a dense cloud of vapour. Calculations performed by the Health and Safety Laboratory (HSL) suggest that, after primary droplet break-up was complete, falling liquid and vapour rapidly reached equilibrium at the centre of the showers. Equilibrium between vapour and liquid represents an upper bound to the amount of evaporation from the liquid that may occur under a given set of conditions.

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Tank

Wi

Defl

nd Girder

ector Plate

Liquid Flow

Liquid breaks into droplets

Tank

Wind Girder

Deflector Plate

Liquid Flow

Liquid breaks into droplets

Figure 17 Mechanism of Vapour Formation

8.1.1 Sensitivity to Source Geometry

The geometries of the tank and of the showers of liquid are important parameters in determining the rate of vapour formation. Of particular importance are the number and width of the cascades of liquid droplets. In the Buncefield case there were eight such cascades, one for each vent in the tank roof (see Figure 18). The width of the cascade is determined principally by the spreading of the flowing liquid over the tank roof prior to reaching the roof edge.

On the basis of discussion with HSL experts involved in the investigation, it is thought that moderate changes in liquid flow rate from the vent only produce small changes in the width of the flow. Hence, given that the total filling rate is of the order of hundreds of cubic metres per hour, the rate of vapour generation is not considered to be sensitive to moderate changes in

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