Recommendations of the Austrian Permanent Seveso Working Group

as a basis to determine appropriate distances for the purpose of land-use planning

according to Council Directive 96/82/EC of 9 December 1996 on the control of major accident hazards involving dangerous substances (Seveso II Directive) as amended by the Directive 2003/105/EC of the European Parliament and of the Council of

16 December 2003

June 2005

Editor:

Magistrat LinzUmwelt- und Technik-CenterHauptstraße 1 – 54041 Linz

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Table of Contents:

Chapter Contents PageList of Abbreviations 4

0 Introduction 5The Austrian Permanent Seveso Working Group 5

1 The Seveso II - Directive and its Effects on Land-use Planning 61.0 Preamble 61.1 The Provisions of the Directive 71.2 Observations on the Determination of "Appropriate Distances" 102 The Recommendation of the Austrian Permanent Seveso

Working Group 12

2.1 Threshold-Quantity-Related Distance Model for Industrial establishments

12

2.2 Standardised Case-by-Case Assessment 15Types of Effects for Case-by-Case Assessment 18

2.2.1 Shock wave 182.2.2 Thermal radiation 192.2.3 Toxic effects 203 Computational Parameters for Standardised Case-by-Case-

Assessment 23

3.1 Source Term Calculation 233.2 Pressure Propagation 233.3 Thermal Radiation 243.3.1 Pool fires 243.3.2 Thermal radiation in case of BLEVE and UVCE 243.4 Dispersion of Toxic Gasses and Vapours 244 References 26

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List of abbreviations:

AEGL Acute Exposure Guideline LevelBLEVE Boiling Liquid Expanding Vapour ExplosionBMLFUW Bundesministerium für Land- und Forstwirtschaft, Umwelt und

Wasserwirtschaft (= Ministry for Agriculture, Forestry, the Environment and Water Management)

BMWA Bundesministerium für Wirtschaft und Arbeit (=Ministry for Economy and Labour)

DN Diameter InsideEC European CommunityERPG Emergency Response Planning GuidelinesEU European UnionIDLH Immediately Dangerous to Life or Health MAC Maximum Allowable ConcentrationMS Member StateÖFAS Österreichisches Forum Anlagensicherheit (= Austrian

Association for Industrial Safety)RHAD Risk/Hazard Assessment DatabaseTDU Thermal Dose UnitTEEL Temporary Emergency Exposure LimitsUVCE Unconfined Vapour Cloud ExplosionVCI Verband der Chemischen Industrie (Germany; Association of

Chemical Industry)

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0 Introduction

The Austrian Permanent Seveso Working Group

The Austrian Permanent Seveso Working Group (hereinafter referred to as the "Working Group”) is a permanent panel of experts, which was constituted in 1992 when the Major Accident Ordinance came into force. Since its foundation, the Working Group has met on a regular basis at least twice a year. Apart from the exchange of experiences among experts on technical-practical as well as legal matters regarding its implementation in the area of industrial accident law and (industrial) safety technology, its activities also include provision for adequate training of the colleagues concerned. To this end, reports and documents are requested regularly from international and EU bodies which are discussed and conclusions drawn for the Austrian situation. This includes also the invitation of international experts to special seminars. Another important task is the deliberation of harmonised guidelines for the implementation of the Directive, in particular for the officially appointed technical experts and, upon request, to offer advice to the respective authorities and ministries.

Since the coming into force of Directive 96/82/EC, the Working Group has established a guideline for inspections according to Art. 18 of the Directive and has been instrumental in elaborating the guideline of the Federal Ministry of Economic Affairs for the "assessment of safety reports according to Directive 96/82/EC ('Seveso II')".The Working Group is composed of representatives of the respective ministries, i.e. the Federal Ministry of Economic Affairs and Labour and the Federal Ministry of Agriculture and Forestry, Environment and Water Management, delegates from all nine Laender, the cities Linz and Salzburg as well as the official Austrian representative for Directive 96/82/E. Currently, the Working Group is the only national body to deal extensively with matters arising from the Seveso II Directive.

Chairman of the Working Group:Dipl.-Ing. Ernst SimonAmt der Steiermärkischen Landesregierung, Fachabt. 17BAlberstraße 1, 8010 Graz

Head of the Working Group "Reference Scenarios":Dipl.-Ing. Martin SonnleitnerMagistrat Linz, Umwelt- und Technik-CenterHauptstraße 1-5, 4041 Linz

While this document has no legally binding effect on land-use planning, the Conference of the Austrian Regional Ministers of the Environment deems the "dual system to determine adequate distances" as proposed by the Working Group suitable for the consultation procedure to ensure a uniform and practicable approach in Austria until the EU database is available (decision of the Conference of Austrian Regional Ministers of the Environment of 15 and 16 June 2005).

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1 The Seveso II Directive and its Effects on Land-use Planning

1.0 Preamble

The modelling of the effects of industrial accidents is influenced by a large number of parameters and assumptions. As a consequence, unacceptable differences in the calculation of distances for one and the same establishment have been noted. Comparisons made by the Technical Working Group 5, Land-use Planning (TWG 5), throughout the EU have shown differences of between 20 and 1500 m for LPG installations and between 200 and 1000 m for ammonia installations. These calculations also reflect the Austrian experience made so far.

Furthermore it is important to point out that several Member States use both the deterministic and probabilistic approach for determining distances.

For this reason, the Commission was asked to incorporate guidelines concerning the definition of a technical database including risk data and risk scenarios in the latest amendment of SEVESO II.

Thus, on a medium-term basis, it to be expected that the probabilistic approach will gain in importance throughout the EU. This trend has prompted the German-speaking Member States in particular to reconsider their deterministic approach chiefly adopted so far. In Germany, the Major Accident Commission is working on a paper which is to provide for adequate distances for new establishments and which is already based on probabilistic considerations. The German Major Accident Commission believes that this should also help to avoid the high incidence of conservative assumptions.

In Austria, recommendations taking into consideration not only deterministic but also probabilistic approaches were elaborated as early as 2002. With the update contained in this document, the request put forth to the Working Group by the Conference of Austrian Regional Ministers of the Environment has been heeded, which is to discuss anew the matter of "eligible protective measures" and the determination and demarcation of risk zones as well as to elaborate proposals. This document is also intended to avoid a stalemate in the development of land-use planning, which might occur if the publication of the EU database is waited for.

What is new is the incorporation of a distance model (as discussed in Germany) developed by the Working Group. This model for the determination of adequate distances largely tallies in the majority of its results with the distances ascertained in the MIACC Guide (Canada). The MIACC Guide has been used as a benchmark because it has been found to be the only model currently available which has been tested in practice and which has been published (a strong focus on risk considerations based on the assumption of a individual fatality risk of 10 -6 / year underlies this screening tool).

Moreover, as in the past, individual cases may also be considered in exceptional cases if required, which, according to the present body of scientific knowledge are in line in their methodology with expected EU approaches. Since the assumptions to be made for the consideration of individual cases are all within the scope of forecasts, this Recommendation also proposes laying down calculation models and parameters

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to achieve standardisation and to prevent undue scattering of results (see Chapter 2.2).

What is also new is that this Recommendation is to be employed exclusively as a basis to determine adequate distances for the purpose of land-use planning and no longer for domino effects and disaster prevention purposes. This is due to the fact that the calculation models as outlined in Chapter 2 neither provide a safe limit nor are they able to cover all possible accident scenarios. Instead, this Recommendation, in the long term, is to heed the request to maintain an adequate distance between industrial establishments and residential areas, public buildings, etc. This approach is also in line with current EU practice.

Since this Recommendation is intended only for the purpose of land-use planning, disaster prevention authorities will now have to base the design of their off-site emergency plans on considerations of their own, which ideally should include specifications on appropriate distances as well.

In summary and considering the above, the Working Group decided to revise the Recommendation, issue Nov. 2002 with a focus on the following priorities:

1. Proposal concerning the application of threshold quantity-related distance model (Chapter 2.1)

2. Standardised case-by-case appraisal (Chapter 2.2)

- also taking into consideration active technical protective measures as mitigation measures

- avoiding a high incidence of conservative assumptions

- determining calculation models and parameters.

It is pointed out once again that this first update of the Recommendation by the Working Group is intended to serve as a practical basis for the determination of appropriate distances in the current phase. Once the guidelines of the EU Commission have been published, the necessity for a further update, if any, will be examined.

1.1 The Provisions of the Directive

Directive 96/82/EC (Seveso II- Directive)1 as amended by Directive 2003/105/EC, which replaces Directive 82/501/EEC (Seveso Directive), is intended to prevent major accidents involving dangerous substances and to limit their consequences for man and the environment2, with a view to ensuring high levels of protection throughout the Community. Contrary and complementary to the preceding Directive, it is not only geared to ensure the "technical safety of establishments" and to prevent disasters, but - above all having seen the results of extremely severe industrial

1 Directive 96/82/EC of the Council of 9 December 1996 on the control of major-accident hazards involving dangerous substances (OJ L 10, 13.1.1997, p.1) as amended by Directive 2003/105/EC of the European Parliament and of the Council of 16 December 2003 (OJ L345, 31.12.2003, p. 97.2 Cp. Art. 1 of the Directive.

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accidents especially in the 80s, such as in México City in 19843 and in Bhopal in 19844 - introduces further instruments to attain this goal as far as possible.

One of these instruments is Land-use Planning (Art. 12 of the Directive RL).

The major industrial accident on 21 September 2001 in Toulouse, where the explosion of huge amounts of ammonium nitrate caused enormous and widespread damage to industrial establishments, residential areas and urban infrastructure as well as to schools, hospital and heavily used transport infrastructure5, alerted the international and European public yet again to the issue of land-use planning and the incompatibilities arising from industrial areas too close to other areas as well as from other sensitive uses.

Art. 12 of the Directive contains provisions concerning control on land-use planning6

in the vicinity of "Seveso establishments". In the recitals No 4 and 22 of the Directive 96/82/EC, explicit mention is made of the importance of maintaining appropriate distances between "Seveso establishments" and settlements in the vicinity of such establishments7. Art. 12 requests that the aim to prevent major accidents and to limit their consequences be taken into account by the Member States in their land-use planning policies and other relevant policies8.

It stipulates that in siting new establishments or modifying existing ones, which may increase the risk or consequences of major accidents, as well as in case of new developments in the vicinity of existing establishments, such as new transport links, locations frequented by the public and residential areas, appropriate distances shall maintained to ensure that the risk of a major accident will not be increased or its consequences aggravated9.

The following 4 cases must be distinguished:

3 The explosion of an LPG storage tank with a storage capacity of 15 m l with a series of BLEVEs claimed hundreds of lives and left thousands of people injured. Official data on the number of fatalities vary between 600 to far beyond one thousand.4 This industrial disaster at the Union Carbide plant in the Indian town of Bhopal , during which major quantities of methyl isocyanate were released, killed thousands of people and left several thousands more injured or suffering from the sequelae.5 30 fatalities, 2500 persons injured, damage at least 1.5 – 2 bn €. The report by the General Inspectorate for the Environment of 24 October 2001 is available on the internet at: http://www.ladocfrancaise.gouv.fr/brp/notices/014000809.shtml6 The official German heading of Art. 12 of the Directive “Überwachung der Ansiedlung“ is somewhat unfortunate wording. The English text reads “Land-use Planning“, which - literally translated - means “Raumordnung“ or. “Flächenwidmung“ in German.7 This again refers to the two industrial disasters in México City and Bhopal, where the lack of suitable distances between residential areas and the industrial establishments was to be blamed for the huge number of fatalities and people injured or having sustained lasting damage.8 Art 12, para.1.9 Art 12 para.1 (a and c).

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1 Existing establishment Existing land use No case10

2 Existing establishment New development in the vicinity

distances

3 New establishment of modification

Existing land use distances

4 New establishment or modification

New development in the vicinity

distances (rather rare)

Table 1

As far as existing establishments are concerned, additional technical measures have to be taken so as not to increase the risk to people11, whereby such measures can be taken on site as well as off site. Art. 12, Para.2 furthermore stipulates that appropriate consultation procedures be set up to facilitate (concrete) implementation.

Art. 12 reads as follows:

Article 12

Land-use Planning

1. Member States shall ensure that the objectives of preventing major accidents and limiting the consequences of such accidents are taken into account in their land-use policies and/or other relevant policies. They shall pursue those objectives through controls on:

(a) the siting of new establishments,

(b) modifications to existing establishments covered by Article 10,

(c) new developments such as transport links, locations frequented by the public and residential areas in the vicinity of existing establishments, where the siting or developments are such as to increase the risk or consequences of a major accident.

Member States shall ensure that their land-use and/or other relevant policies and the procedures for implementing those policies take account of the need, in the long term, to maintain appropriate distances between establishments covered by this Directive and residential areas, areas of public use; major transport routes as far as possible, recreational areas and areas of particular natural sensitivity or interest, and, in the case of existing establishments, of the need for additional technical measures in accordance with Article 5 so as not to increase the risks to people.

10 Protection of vested rights! In this case, other instruments of the Directive have to be employed, such as technical/management specific measures or provisions of prevention by appropriate (off-site) emergency planning.11 Art. 12 Para.1 (b). The case applies if a modification to an existing establishment is planned and if such modification increases the risk of an accident while the existing land-use scheme remains unchanged. Moreover, it seems to be increasingly common practice in the EU to reduce appropriate distances by technical measures of appropriate quality and in sufficient availability (either on site or off site) intended to limit any such accidents in their consequences and impact.

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1a. The Commission is invited by 31 December 2006, in close co-operation with the Member States, to draw up guidelines defining a technical database including risk data and risk scenarios, to be used for assessing the compatibility between the establishments covered by this Directive and the areas described in paragraph 1. The definition of this database shall, as far as possible, take account of the evaluations made by the competent authorities, the information obtained from operators and all other relevant information such as the socio-economic benefits of development and the mitigating effects of emergency plans.

2. Member States shall ensure that all competent authorities and planning authorities responsible for decisions in this area set up appropriate consultation procedures to facilitate implementation of the policies established under paragraph 1. The procedures shall be designed to ensure that technical advice on the risks arising from the establishment is available, either on a case-by-case or on a generic basis, when decisions are taken.

1.2 Observations on the Determination of "Appropriate Distances"

The only basis available so far in Austria to determine appropriate distances to/from "Seveso establishments" were reference scenarios coupled with dispersion models (mainly for pressure, thermal radiation and toxic gases) and acceptance criteria (end points). The preparation and calculation of such scenarios, in particular for severe accidents involving dangerous substances, had no tradition in Austria prior to the enforcement of the Seveso II Directive. Thus it was and is still necessary to resort to EU and international experience.

Within the Community but also in other countries12 longer traditions existed with regard to the determination of distances to/from "Seveso establishments", with two trends being chiefly pursued. The "determinists" select certain scenarios and evaluate their consequences13. The "probabilists" determine the (arithmetic) probability of a specific accident or of the extent of damage14,15. Apart from these, there are “hybrid approaches” composed of both trends. However, it is most likely that the probabilistic approach will prevail in the end.16

At any rate, in order to comply with the requirements of Art. 12 of the Directive, a reasonable approach towards planning and decision-making had to be sought. The Working Group took this issue on board in the wake of an expert seminar held by the Austrian Forum for the Safety of Installations (ÖFAS)17 in April 1996. Apart from internal discussions among experts and calculations based on international technical

12 E.g.. Canada, Major Industrial Accidents Council of Canada (MIACC): Risk Assessment Guidelines for Municipalities and Industries. An Initial Screening Tool. Major Industrial Accidents Council of Canada 1997 (MIACC-Guide)13 For instance in France. First attempts also in Germany.14 For instance in the United Kingdom, the Netherlands and Canada15A good survey on the approaches adopted by the (then 12) Member States is given by C. Hamilton, R. de Cort, K. O. Donnel (HSE): Report on Land Use Planning Controls for Major Hazard Installations in the European Union. Ed.. CDICR-Ispra, 1990. EUR 15700 EN. For definitions on deterministic and probabilistic approaches cp. Hamilton et al. aaO, 10.16 See amendment of Directive 96/82/EC by Directive 2003/105/EC; Article 12 Para. 1a.17 ÖAFS is the Austrian association of officially appointed experts dealing with safety technology matters and industrial accident law.

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literature, two studies were commissioned, based on which the decision for the original Recommendation was taken. These studies are:

- H. Koinig, Reference Scenarios according to Directive 96/82/EC, Final Report, Vienna 1999, commissioned by the Federal Ministry of Agriculture, Forestry, Environment and Water Management, and

- R. Pischinger, P. Sturm et al., Reference Scenarios "Dispersion of Toxic Gases" for the Purpose of Land-use Planning according to Art. 12 of the Seveso II Directive", Graz, 2000; commissioned by the Laender Carinthia, Salzburg, Styria, Tyrol, Vorarlberg and Vienna and the City of Linz.

A fundamental decision was then taken to chose the deterministic approach and thus to base calculations largely on worst case scenarios. The use of a probabilistic approach, namely databases concerning the probable failure rate of components etc., did not appear to be meaningful at that time since the Working Group did not believe that the data material then available were sufficiently reliable.Finally, in November 2002, the “Recommendation of the Austrian Seveso Working Group for the Calculation of Appropriate Distances for the Purpose of Land-use Planning, Emergency Planning and Domino Effects” was published.Meanwhile the general view has gained acceptance throughout the EU that reference scenarios in the context of appropriate distances are not to be equated with worst-case scenarios for the purpose of emergency planning. As a consequence and quite correctly, the trend when designing such scenarios is to use risk data (risk scenarios). To date, there are still too few reliable data available so that the EU Commission will draw up at least guidelines on the definition of a technical database (RHAD) by 31 December 200618.In view of the greatly differing nature of industrial installations and the required effort, it remains to be seen whether - in analogy to the risk assessment of nuclear power plants - a purely probabilistic approach will be widely accepted. Currently, a kind of "mixed from" appears to be a likely solution, meaning that quasi-deterministic approaches are backed by risk considerations (e.g. the as yet unpublished recommendations of SFK/TAA – Working Group "Monitoring of Land-use Planning in Germany" or the MIACC-Guide12). Considering all these facts and circumstances, the Working Group has agreed to adapt the Recommendation in a first update so as to take account of this development and, in particular, of the discussion throughout the EU as it stands today. Once the RHAD has been published, the need for a further update will be examined.The following proposals and suggested modes of calculation are also to be seen against this background.

The recommendations given below are intended to assist the competent authorities in the consultation procedure to be set up19 in determining appropriate distances by balancing the interests between the need to protect the population and to safeguard economic and settlement development.

18 Article 12 Para.1a.19 Article 12 Para.2.

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2 The Recommendation of the Austrian Permanent Seveso Working Group

In view of the lack of a binding definition of "appropriate distance", the Working Group has based its Recommendation on the following assumptions:The appropriate distance- is one of several instruments to reduce the risk to the neighbourhood;- is unable to prevent all possible consequences of industrial accidents in

neighbouring zones lying outside the distance;- is not a safe limit;- is laid down to achieve, on a long-term basis, a separation between industrial

zones and sensitive areas;- should, ultimately, be a political consensus and the result of balancing a great

number of interests, inter alia, the interest between industry and labour on the one hand and between the need of protecting the neighbour on the other.

2.1 Threshold-Quantity-Related Distance Model for Industrial Establishments

The best-suited model to provide a uniform basis for the consultation procedure to determine appropriate distances, especially for newly planned establishments but also for existing Seveso establishments, is the threshold-quantity-related distance model. This model presupposes that the establishment is a state-of-the-art installation.

The model is based on the following framework conditions:- a distance of 100m if the lower threshold quantity is reached;- a distance of 300 m if the upper threshold quantity is reached; and- a distance of approx. 1000m if the 100-fold upper threshold quantity is reached; - linear interpolation is applied up to the upper threshold quantity; a logarithmic

approach is adopted for values above.

The distance model is described by the following formula:

For

and resp.

applies, with the larger distance being the applicable one.

For and

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and resp.

applies, with the larger distance being the applicable one.

For the following applies:

distance proposed for the consultation procedure to determine the appropriate distance [m]

specified to be 100 m

quantity of dangerous substance [ t ] number of dangerous substances or categories of substances present in the establishment or installation in question. The Directive’s summation rules are to be observed.threshold quantity column 2 [ t ]threshold quantity column 3 [ t ]

If no is specified in the Directive, .

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as

qi/Qi1 3 10

100

300

Figure: Example for possible curve patterns in the threshold quantity-related distance model

Account is to be taken of all dangerous substances which may be present in an establishment or installation within the meaning of Article 3, Para. 2 of the Directive whereby these substances are classified in groups or categories according to the summation rule pursuant to Annex I, Part 2 of the Directive. For each of these groups or categories of substances, the distance for this establishment or installation is to be calculated, whereby the largest distance shall apply.

These formulae are mathematical models, which – like the Risk Assessment Guidelines for Municipalities and Industries, Edition 1997’ (MIACC-Guide) – use a logarithmic approach for the risk to be calculated. However, contrary to the MIACC-Guide, these formulae are applicable to all substances and categories of substances listed in the Directive.

The formulae are based solely on the threshold quantities as specified in the Directive and the quantities present in the establishment or installation. They thus represent the potential hazard of a substance in analogy to the Directive.

In many cases, the distances as determined by the formula correspond, by and large, to the distances proposed in the guidelines and commonly adhered to in the EU Member States.By using the distance formulae, uncertainties concerning the assumptions and parameters to be chosen for the calculation are avoided. Another advantage is that, by adopting this approach, uniform distances are laid down throughout Austria for establishments having the same quantities of substances present. The calculated distance is to be maintained for each establishment pursuant to Article 3 (2) of the Directive – starting from the area within an establishment in which the major technical units together with the respective substances are located.

Examples of calculations:

Part/no. Substance Qualifying (threshold)

quantities [t]

Quantity [t] Distance [m]

1/6 chlorine 10 / 25 100 4401/14 LPG/natural gas 50 / 200 100

1,000150460

1/18 methanol 500 / 5,000 1,000 1201/30 petroleum products 2,500 / 25,000 100,000 4402/1 Very toxic

substances5 / 20 5

50100390

2/2 ammonia 50 / 200 10010,000

150690

2/2 toxic substances 50 / 200 1001,000

150460

2/8 Extremely flammable liquids R11

5,000 / 50,000 10,000100,000

120370

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2.2 Standardised Case-by-Case assessment

Distances must normally not fall short of the distances as determined according to 2.1. Exceptions may be granted in the case of existing establishments if it can be proved that additional (technical) measures or measures beyond the state of the art which warrant a reduction of the distance have been taken, whereby other specific local conditions may also be taken into consideration. These case-by-case assessments are to be based on the conditions and modes of calculation specified below (see also Chapter 3).

Immission guidance values for standardised case-by-case assessments:

Table 2:Substance Scenario Impact Assessment valueliquefied flammable gases

BLEVE, UVCE a) shock waveb) thermal

radiation

a) 0.050 barb) 500 TDU for the dynamic-thermal assessment a short-term impact of <60 seconds is considered and calculated according to the formula TDU=(kW/m²)4/3. sec

flammable liquid substance

fire in the largest section/pool20

thermal radiation 3.0kW/m²

Explosives explosion of the biggest mass stored together

shock wave 0.050 bar

explosive gas/vapour cloud

UVCE after 1 minute;release over a 25 cm pipe diameter (DN 250) for 10 min)21, 22

shock wave 0.050 bar

toxic substances release over a 25 cm pipe diameter (DN 250) for 10 min)21,22

effect on human health

IDLH23

20 This also applies to the storage of barrels or storage of smaller-sized containers. 21 The pipe releasing the largest quantity in case of an accident is to be assumed. For a pipe larger in diameter than DN 50, a total rupture is not to be assumed. 22 The time of intervention can be reduced if justified by the existence of passive or active safety devices.23 These values can also be obtained from the following website: http://www.cdc.gov/niosh/idlh/intridl4.html.See also Chapter 2.2.3

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To obtain, as far as possible, uniform results, the following boundary conditions were laid down by the Working Group:

1. The scenarios listed above shall apply to technical installations in which dangerous substances may be present and if these are applicable for the determination of distances. Account shall also be taken of installations using, handling or storing dangerous substances which have not led to the classification as “Seveso establishments”

2. Missiles will generally only have spot character in their effect (contrary to explosions, toxic gas clouds and the like) and shall not be taken into account. However, there may be cases where their inclusion may be justified (e.g. storage of gas bottles, acetylene).

3. Containment measures shall, as a matter of principle, be passive safety measures. Passive safety measures include, inter alia, retention pools and similar retention systems, shock-proof design of the enclosure, encasements, fire-protective coatings, earth dams and ramparts, precautions against pipe fractures, check valves, bursting disks. Containment measures in the form of active safety measures24 may be eligible if proof can be furnished of their sufficient availability. This is the case, for instance, if a redundant design of the containment device exists and a fail-safe design thereof exists25.

4. The scenarios listed in Table 2 shall be applicable to transport vehicles only inasmuch as their operation is connected directly with the activity of the establishment. This is the case, for instance, during loading or unloading operations or if these vessels or vehicles are used as a means of storage (§84b Trade Regulation Act). On-site transportation by vessels / vehicles is excluded until the loading / unloading facility.

5. The failure of a pressurised vessel under thermal impact need not be taken into account if eligible safety measure are in place (Point 3) or if safety distances calculated according to "Druckbehälteraufstellungsverordnung" (Austrian Ordinance concerning the installation of pressurised vessels) are maintained, provided these safety measures are able to prevent an exposure of these vessels to unduly high thermal radiation or an unduly high rise of pressure in these vessels. For rail tankers and road tankers, the special case applies inasmuch as these containers do not possess safety valves and that therefore the permissible heat radiation to which they may be exposed is accordingly low For temporary fire loads (e.g. motor vehicles), the appropriate distance shall be determined by calculation, whereby the minimum distance as laid down in the "Druckbehälteraufstellungsverordnung" is 5 m. Spontaneous failure and auto-ignition of transport vehicles are events which do not fall under the requirements of "appropriate distances".

24 §2 (9) Industrial Accident Ordinance, Austrian Federal Law Gazette 354/2002 of 27 November 200225 Note: The Working Group had initially intended to take over the definitions of the IEC 61511 "Functional Safety - Safety Systems for the Process Industry " for their own definition of active safety measures. However, in view of the lack of experience in dealing with this standard and due to the lack of data, it refrained from doing so.

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6. In cases where a BLEVE has not to be taken into account due to the presence of passive safety devices (Point 3), a UVCE is to be calculated, as in cases of explosive gas/vapour clouds.

7. For diameters larger than DN 250, a leakage corresponding to DN 250 is assumed.26.

8. In case of an UVCE, an intervention time of 10 min is assumed. For determining the effect of the UVCE, the amount of gas released within 60 sec shall be taken into account, whereby ignition is assumed to have taken place at the point of release27. The damming factor shall be determined on a case-by-case basis.

9. For liquid and solid oxidising substances an examination shall take place if scenarios or effects as listed in Table 2 are possible. These shall then be considered in analogy.

10. For substances dangerous to the environment no scenario is usually relevant for the purpose of land-use planning unless these substances possess other dangerous properties.

11. Conflagration gases are not specific to Seveso establishments and are therefore not considered when determining appropriate distances (see Chapter 3.3). If required, their effect may be considered in emergency planning.

12. There may also be other scenarios (e.g. continuous exothermal reactions).

13. The distance shall be determined from the source.

14. For installations with toxic or carcinogenic substances for which no assessment value is specified, a standardised case-by-case approach is not possible.

26 This "limit diameter" is based on the result of the ENCONET Study according to which 96% of all pipe fractures occur in pipes of a diameter of up to DN 250.27 Cp.: Scénario B: UVCE in: Secrétariat d’Etat auprès du Premier ministre chargé de l’Environnement et de la Prévention des risques technologiques et naturels majeurs – DEPPR – Service de l’Environnement industriel (Ed), Maitrise de l’Urbanisation autour des Sites Industriels à Haut Risque, Paris, October 1990, p 30f.

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Types of Effects for Case-by-Case Assessment

2.2.1 Shock wave

For land-use planning purposes a threshold value of 50 - 70 mbar (irreversible damage to humans) has been laid down internationally for the surroundings. Considering the instantaneous effect of such shock waves which make escape impossible, the Working Group proposes a value of 50 mbar.

Examples28:

Overpressure (mbar)

Effects on humans

6 hurricane with wind force 1210 a blast of wind knocks down persons standing 30 slight injuries caused by glass fragments70 no injuries in open terrain

80 – 90 a blast of wind sweeps away persons lying (360 km/h)170 1% rupture of the ear drum300 fatalities and injuries within collapsing buildings480 70% fatalities and injuries in the open2000 99% lung rupture

Effects on buildings and installations (parts thereof)

2 breakage of large window panes possible10 standard value for window breakages30 confined structural damage50 minor structural damage to buildings60 99% of all window panes break70 partial destruction of buildings, danger of collapse

170 50% walls of buildings damaged210-280 destruction of light constructions, rupture of empty crude oil tanks340-410 total destruction of buildings

28 Cp. Damage Assessment, Department of the Interior of the Canton of Zurich, Emergency Response Co-ordination Centre, Zurich, June 1992.

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2.2.2 Thermal radiation

For land-use planning purposes a threshold of 3 - 5 kW/m² (irreversible damage to humans) has been laid down internationally. Considering that an escape will not be possible equally for all persons, the Working Group proposes a value of 3.0 kW/m² and of 500 TDU for short-term impacts.

Examples29:

Thermal radiation (kW/m²)

Effect on humans

1 maximum solar irradiation1.5 no adverse effects even with longer exposure4.5 formation of blisters after 20 sec.

12.5 first-degree burns after 10 sec.36 third-degree burns after 10 sec.

Effects on emergency-response teams

4.5 fire-fighting action without cooled fire-fighting suits 8 short-term fire fighting action with cooled fire-fighting suits

12.5 If cooled, tanks are not damaged36 tanks are damaged in spite of cooling

Effects on constructions and installations (parts thereof)

2 destruction of varnish surfaces on timber after 30 min.3 destruction of synthetic surfaces after approx. 30 min.

4.5 ignition of felt roofing upon flame contact12.5 bursting of glass panes after 10 min.25 ignition of timber without flame contact30 deformation of steel profiles after 30 min.

100 ignition of roof insulation covered with aluminium plates, failure of load-bearing steel profiles after 20 min.

29 Cp. Damage Assessment, Department of the Interior of the Canton of Zurich, Emergency Response Co-ordination Centre, Zurich, June 1992

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2.2.3 Toxic effects

The assessment of the immission load caused by an accidental release of toxic substances shall be based on the consideration when determining the threshold that this is an extremely rare event and, if occurring, of short-term impact only. This is why thresholds are applied assuming an impact of 30 – 60 minutes in duration. The application of MAK values, which are geared to frequent and long-term exposure, are not suitable at all.

IDLH values (Immediately Dangerous to Life or Health)is a concentration at which escape is possible within 30 minutes without causing irreversible damage to health even without breathing equipment.

ERPG values (Emergency Response Planning Guidelines)

ERPG 1 is assumed to be the maximum airborne concentration to which almost all individuals may be exposed for up to one hour without sustaining more than mild, transient damage to health or perceiving a clearly defined objectionable odour.

ERPG 2 is assumed to be the maximum airborne concentration to which almost all persons may be exposed for up to one hour without sustaining or developing irreversible or other serious damage to health or symptoms which might impair a person’s ability to take protective measures.

ERPG 3 is assumed to be the maximum airborne concentration to which, if not exceeded, almost all individuals may be exposed for up to one hour without sustaining or developing life-threatening damage to health.

AEGL values (Acute Exposure Guideline Levels)

AEGL 1 is the airborne concentration of substances (expressed in ppm or mg/l) at which, if exceeded, the population at large including sensitive but excluding hypersensitive individuals may experience perceptible indisposition. Airborne concentrations of substances below the AEGL 1 represent exposure levels which may be slightly irritant to the sense of odour, taste or other senses.

AEGL 2 is the airborne concentration of substances (expressed in ppm or mg/l) at which, if exceeded, the general population including sensitive but excluding hypersensitive individuals may sustain irreversible or other serious long-term damage including damage which might impair a person’s ability to escape. Airborne concentrations of substances below the AEGL 2 value but above the AEGL 1 represent exposure levels which may cause perceptible indisposition.

AEGL 3 is the airborne concentration of substances (expressed in ppm or mg/1) at which, if exceeded, the population at large including sensitive but excluding hypersensitive

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persons may sustain life-threatening damage or perish. Airborne concentrations of substances below the AEGL 3 value but above the AEGL 2 value represent exposure levels which may cause irreversible or other serious long-term damage including damage which may impair a person’s ability to escape.

TEEL values (Temporary Emergency Exposure Limits)

TEEL 0is the threshold concentration below which most people will experience no adverse health effects.

TEEL 1is assumed to be the maximum airborne concentration to which almost all individuals may be exposed up for one hour without sustaining more than mild, transient damage to health or perceiving a clearly defined objectionable odour.

TEEL 2is assumed to be the maximum airborne concentration to which, if not exceeded, almost all individuals may be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual’s ability to take protective action.

TEEL 3is assumed to be the maximum airborne concentration to which, if not exceeded, almost all individuals may be exposed for up to 1 hour without sustaining or developing life–threatening damage.

In Austria, the IDLH value is favoured by the Working Group. However, changes are foreseeable. The US Environmental Protection Agency together with several Member States are elaborating and jointly publishing threshold values (AEGL – Acute Exposure Guideline Level) which, once accorded internationally, might become applicable. In the Risk/Hazard Assessment Database (RHAD), which is in the making, the European Commission is expected to propose AEGL2 and AEGL3 for the two-zone model, if not available, ERPG2 and ERPG3. Similarly to the US AEGL values, so-called AETL values (Acute Exposure Threshold Levels) are currently being prepared at European level for 21 different substances. These values might also be incorporated into the RHAD.

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Comparison Toxicity Data

Sub-stance

IDLH ERPG (60 min)AEGL (30 and 60 min

resp.)MAC 2003

 (30

min)ERPG2 ERPG3

publ.

AEGL2 (30)

AEGL2 (60)

AEGL3 (30)

AEGL3 (60)

Status**

Mv***

Sv***

NH3 300 150 750 2000 160 110 1600 1200 int. 20 50

SO2 100 3 15 1989 1 1 32 27 prop. 2 4

Cl 10 3 20 1988 2.8 2 28 20 int. 0.5 0.5

HF 302050

(10min)

50170 (10

min)

19971999

34 24 62 44 int. 1.8 3

H2S 100 30 100 1991 32 27 59 50 int. 10 10

Acrolein 2 0.5 3 1989 0.18 0.1 2.5 1.4 prop. 0.1 0.1

Br 3 0.5 5 2001 0.33 0.24 12 8.5 prop. 0.1 0.1

POCl3 - 0.5* 3* ? - - 1.1 0.85 int. 0.2 0.8

PCl3 25 3* 15* ? 2.5 2 7 5.6 int. 0.25 0.5

BF3 25 10 33 1999 6.2 3.1 27 14 int. 1 1

CS2 500 50 500 2002 200 160 600 480 prop. 10 40

TDI 2.5 0.15 0.6 2002 0.17 0.083 0.65 0.51 int.0.00

50.02

Styrol 700 250 1000 1995 160 130 1900 1100 prop. 20 80

Remarks:all values in ppmMAC maximum allowable concentration* TEEL values** int. = interim, prop. = proposed*** Mv = daily mean value, Sv short-term value/instantaneous valueIDLH unchanged at least since 1996

Calculation modelFor the scenario "dispersion of toxic gases", the choice of the calculation model is essential when determining the appropriate distance. To investigate this further, a study was commissioned by the Austrian Laender of Carinthia, Styria and Salzburg to Graz University of Technology, which screened the large number of programmes available on the market and evaluated them on the basis of certain criteria. As a result of this study, the following computational programmes were recommended: TSCREEN, SLAB, RMP, ALOHA (CAMEO), HGSYSTEM . Other models, such as Effects/TNO, MET-Model, VDI, etc. may be employed as well.However, it has to be borne in mind, that the result may vary quite considerably from programme to programme for the same task. The Working Group believes that considerable efforts still have to be invested in this respect to achieve international harmonisation.

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3 Computational Parameters for Standardised Case-by-Case-Assessment

As demonstrated so far by practice, computational results regarding the effects of explosions, thermal radiation and release of toxic substances show considerable variations. To avoid a simple listing of worst case approaches, it seems to be meaningful to standardise computational parameters as far as possible in order to obtain results that are comparable across Austria.

3.1 Source Term Calculation

To ensure a uniform approach, it is essential to use the same formula throughout Austria for source term calculation. The so-called UFO Scheme contains a collection of formulae which has turned out to be very useful. Another way of calculating the source term is provided by the programme package ALOHA. Comparative calculations have shown good agreement.

The calculation is based on the following parameters:

- effluent number 0.61

- process parameters (p, T, etc.): conventional operating parameters or mean values (e.g. outdoor vessel 20°C, underground vessel 10°C)

- maximum permissible filling level of vessels

- temperature of ambient air and ground: 20°C

- frictional losses are not considered

- wind speed as a basis for pool evaporation: according to dispersion calculation

- The following minimum pool depths are assumed (UFO Scheme , Annex 4)uneven gravel 25 mmflat gravel 10 mmsand 10 mmconcrete/rock 5 mmunknown 10 mm

3.2 Pressure Propagation

A reliable calculation of blast pressures is not possible, not even if complex numerical calculation procedures are applied. Therefore, methods which allow an assessment based on few parameters that are easy to determine are to be preferred. In general, the use of the TNO Shock Wave Model (Yellow book 1992; cp. also the study by Koinig,1999) is recommended. If, in a specific case, the situation commands special containment measures, the calculation may be performed following the Multi-energy Method (Yellow book 1997) or the method according to Pförtner (footnote: contained, e.g. in the programme package 8feuex).

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3.3 Thermal Radiation

3.3.1 Pool fires

Almost all hydrocarbons generate considerable smoke if burnt in extensive pools. The use of the model according to Schönbucher/Göck30 is recommended. No smoke or little smoke develops if methanol, ethanol, acetaldehyde and other comparable liquids (C-H-O compounds) are burnt. The heat radiated by fires of this kind can be derived from the Stefan-Boltzmann Law. However, it has to be borne in mind that the flame temperature has to be considered to the power of 4 in the calculation and that the emission factor has a major influence as well.

Other parameters:- transmission coefficient = 1 (conservative; attenuation due to air humidity and

carbon dioxide as well as the influence of wind are not considered)- convection should be considered only in case of direct flame contact in

buildings; convection increases the result of thermal radiation by some 20%.

As regards conflagration gases, see Point 3.4.

3.3.2 Thermal radiation in case of BLEVE and UVCE

When assessing the thermal radiation from unconfined vapour cloud explosions (UVCE) or boiling liquid expanding vapour explosion (BLEVE), the method according to Hymes31 may be applied. A value of 30 - 40% without atmospheric attenuation is recommended.

3.4 Dispersion of Toxic Gasses and Vapours

Physical dispersion of the various substances always differs widely and is very complex. It depends on a number of factors such as density, temperature, turbulence, etc. Moreover, local meteorological conditions (wind direction, wind speed, temperature gradient, heat of ground, roughness, air humidity, vertical mixing, solar irradiation, ....) are difficult to capture. In addition, dispersion in close proximity to the source of emission is heavily influenced by the type of source (point/area source), the source altitude as well as by the topography and building structure.Users and commissioning authorities, therefore, have to bear in mind that computational models are merely able to predict roughly the potential effects and that the results may vary considerably depending on the meteorological conditions.

The Working Group, therefore, recommends the use of "standardised average dispersion conditions". These are applied in several other European countries as well (e.g. "Guide to hazardous industrial activities", Netherlands).These dispersion conditions are based on Class D according to Pasquill/Gifford or Class 5 according to Turner/Reuter without considering inversion.Ambient temperature is assumed to be 20°C and wind velocity 2 m/s at 3 m height without considering the distribution of wind direction. As regards surface roughness,

30 is included in various commercially available programme packages.31 is included in various commercially available programme packages

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values reflecting the actual situation are to be used. Further default parameters are 50% cloudiness and 50% relative air humidity.

In case of fire, apart from the spread of thermal radiation, the spread of hazardous substances present in the conflagration gasses is frequently of interest. The propagation of hazardous substances in the conflagration gasses can be neglected in many cases where the fire has developed fully and sufficient oxygen is supplied due to the strong uplift caused by the high heat release, which dilutes hazardous substances in the conflagration gasses close to the ground to non-dangerous levels32.

32 quoted from the UFO scheme, see Chapter 4.

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4 References

The references quoted below do not claim to represent the complete international and EU literature available on this subject. Only references used, inter alia, by the Working Group are cited.

EU:

ISIS (Ed) Guidance on Land Use Planning As Required By Council Directive 96/82/EC (Seveso II), Report No EUR 18695 EN, Ispra 1999 (may also be downloaded from the JRC’s website in Ispra: http://mahb.jrc.it).

Other MS and European States:

Secrétariat d’Etat auprès du Premier ministre chargé de l’Environnement et de la Prévention des risques technologiques et naturels majeurs – DEPPR – Service de l’Environnement industriel (Ed), Maitrise de l’Urbanisation autour des Sites Industriels à Haut Risque, Paris, October 1990.

Direktion des Inneren des Kantons Zürich, Koordinationsstelle für Störfall-vorsorge, Schadenausmaß-Einschätzung, Zurich, June 1992.

Austria:

H. Koinig, Referenzszenarien zur RL 96/82/EG, Endbericht, Wien 1999, commissioned by the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management.

R. Pischinger, P. Sturm et al., Referenzszenario "Ausbreitung toxischer Gase“ für Zwecke der Raumordnung/Flächenwidmung nach Art. 12 der "Seveso II-RL“, Graz, 2000; commissioned by the Laender of Carinthia, Salzburg, Styria, Tyrol, Vorarlberg and Vienna, and the City of Linz.

USA:

Primary and secondary information sources for the SLAB-Database (ENCONET Study).

Canada:

Risk Assessment Guidelines for Municipalities and Industries. An Initial Screening Tool. Major Industrial Accidents Council of Canada 1997 (MIACC-Guide).

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Germany:

Ermittlung und Berechnung von Störfallablaufszenarien nach Maßgabe der 3. Störfallverwaltungsvorschrift; Umweltforschungsplan des Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit (UFO Scheme).

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