Index

Dispersion area types I to V
Area maps for types I to V

Dispersion area types VI to IX
Area maps for types VI to IX

Dispersion area types X to XVIII

Dispersion area types X to XII
Area maps for types X to XII

Dispersion area types XIII to XV
Area maps for types XIII to XV

Dispersion area types XVI to XVIII
Area maps for types XVI to XVIII

Dispersion area types XIX to XXI
Area maps for types XIX to XXII

Area maps for types XXIII to XXV

Table of input data for instantaneous release
Table of input data for continuous release

Dispersion area type I

This type of dispersion area can be used for accidental releases in flat terrain without obstacles. Furthermore, it can replace all the dispersion areas with obstacles which lead to a reduction of the concentration if no special diagrams are available.

Dispersion area type II

This type of dispersion area can be used for accidental releases in which the dispersion is limited by an obstacle to a hemisphere. The obstacle can consist of a row of buildings, a dam, a dock or similar objects near the source. This type of dispersion area may also be used for shorter obstacles or other heights at larger distances, if no other special diagrams are available. If the distance of the obstacle amounts to more than 5 L_ei (for instantaneous release) or 30 L_ee (for continuous release), the effect of the obstacle on the heavy gas dispersion can be disregarded.

Dispersion area type III

This type of dispersion area can be used for accidental releases for which the dispersion is limited by an uninterrupted canyon of orthogonal walls which is parallel to the wind. This type of dispersion area can also be used for canyons of other geometries if no other special diagrams are available therefore. Deeper canyons lead to similar concentrations. For lower, broader or interrupted canyons, it will yield conservative estimations. For single, interrupted buildings, the (*UZD) lower flammability distances are considerably overestimated if the diagram of dispersion area type III is used.

Dispersion area type IV

For this type of dispersion area, a hemispherical, impermeable protective wall is located at such a distance leeward of the source that a distinct protection is obtained for those locations which are situated beyond the wall. On the bases of the results, the potential protection effect of such a measure can be estimated.

Dispersion area type V

In contrast to dispersion area type IV, the protective wall is placed nearer to the source for this type of dispersion area, and the protecting effect decreases.

Area map for dispersion area type I

Flat terrain without obstacles.

Area map for dispersion area type II

Flat terrain. This dispersion is limited to a hemisphere by a wall located near the source and parallel to the wind (Fig. 2). The wall is located at a distance of 1 L_ei (for instantaneous release) or 5.6 L_ee (for continuous release) from the gas source. The wall is to be regarded as infinitely long and, during the heavy gas spread phase, as infinitely high (1L_ei or 5.6 L_ee).

Area map for dispersion area type III

Flat terrain. This dispersion takes place in a canyon of orthogonal walls. This canyon has a height of 1 L_ei (for instantaneous release) or 7 L_ee (for continuous release), and a breadth of 2 L_ei or 28 L_ee, respectively.

Area map for dispersion area type IV

Flat terrain. Semi-circular, massive wall leeward of the source. The height of the wall is 0.4 L_ei (for instantaneous release) or 2.24 L_ee (for continuous release). The distance between the source and the obstacle amounts to 4 L_ei or 22.4 L_ee, respectively.

Area map for dispersion area type V

Flat terrain. Semi-circular, massive wall leeward of the source. The height of the wall is 0.4 L_ei (for instantaneous release) or 2.24 L_ee (for continuous release). The distance between the source and the obstacle amounts to 2.5 L_ei or 14 L_ee, respectively.

Dispersion area type VI

In this dispersion area the wall, already used in dispersion area V, was placed in winward of the source. In contrast with the wall leeward of the source, in the dispersion area V no distinct protection is visible. The concentrations, however, are below those concentrations measured in the area without obstacles. As a reason for this, the shade of the area near the source is to be mentioned. This causes a stronger lateral dispersion of the gas cloud.

Dispersion area type VII

The wall used in this dispersion area corresponds to the obstacle used in the dispersion area IV. Just as in the dispersion area VI, the wall was placed here winward of the source. Although the concentrations are lower here than in the dispersion area without obstacles, not a significant protection is obtained by this obstacle.

Dispersion area type VIII

The obstacle in this dispersion area is in principle a combination of the obstacles used in the dispersion area types V and VI. The circular, impermeable protective wall with the source in the center used here, shows a great distinctive protection for all the locations situated downstream of the source leeward of the protection wall. The position of the protective wall is clearly the cause of the strong concentration gradient. As on the basis of the shade within the protective wall, the gas can spread stronger laterally than in the dispersion area type V, the concentration in the dispersion area VII is generally lower than in the dispersion area type V.

Dispersion area type IX

The circular, impermeable protective wall in this dispersion area corresponds to a combination of the obstacles in the dispersion area IV an VII. Also, as in the dispersion area type VIII, a great distinct protection for locations situated downstream of the source leeward of the protection wall is visible.

Area map for dispersion area type VI

Flat terrain. Semi-circular, massive wall windward of the source. The height of the wall is 0.4 L_ei (for instantaneous release) or 2.24 L_ee (for continuous release). The distance between the source and the obstacle amounts to 2.5 L_ei or 14 Lcc, respectively.

Area map for dispersion area type VII

Flat terrain. Hemispherical, massive wall in luv of the source. The height of the wall is 0.4 L_ei (for instantaneous release) or 2.24 L_ee (for continuous release). The distance between the obstacle and the source amounts to 4L_ei or 22.4 Lcc, respectively.

Area map for dispersion area type VIII

Flat terrain. Circular, massive wall around the source. The height of the wall is 0.4 L_ei (for instantaneous release) or 2.24 L_ee (for continuous release). The distance between the source and the obstacle (radius of the obstacle) amounts to 2.5 L_ei or 14 Lcc, respectively.

Area map for dispersion area type IX

Flat terrain. Circular, massive wall around the source. The height of the wall is 0,4 L_ei (for instantaneous release) or 2,24 L_ee (for continuous release). The distance between the source and the obstacle (radius of the obstacle) amounts to 4 L_ei or 22,4 Lcc, respectively.

The dispersion area types X to XVIII can be used for accidental releases in which the dispersion is limited by an interrupted canyon of orthogonal walls which is parallel to the wind.

In case of an instantaneous release the measured mean UZD are generally lower in these dispersion areas than the UZD measured in an uninterrupted canyon (dispersion area type III). In the dispersion area type X (in continuous release) after 50 L_ee distance from the source, lower UZD than in the dispersion area type III are visible, while the UZD in the dispersion area types XI and XII are generally lower than the values measured in the dispersion area type III.
The greater dilution of the heavy gas cloud is traced back to the greater mixing with ambient air. This is caused by the lateral building gaps.

As it is evident from the concentration courses, a widening of the canyon and the building gaps leads to a reduction of the UZD values.

Area map for dispersion area type X

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 2 L_ei or 14 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 2 L_ei or 14 L_ee wide.
The source is located in the center of the canyon and in the center of a building gap.

Area map for dispersion area type XI

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 3 L_ei or 21 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 3 L_ei or 21 L_ee wide.
The source is located in the center of the canyon and in the center of a building gap.

Area map for dispersion area type XII

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 4 L_ei or 28 L_ee wide.
The lateral walls of the canyon constist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 4 L_ei or 28 L_ee wide.
The source is located in the center of the canyon and in the center of a building gap.

This dispersion area types can be used in principle for the same canyons as the dispersion area types X, XI and XXII, though with a source of different location. As well as in the area types X to XII, a widening of the canyon and the building gaps lead to a reduction of the UZD values.

In case of an instantaneous release the mean UZD values of the area types XIII to XV are generally lower than the UZD measured in the dispersion area type III. In the dispersion area types XIII, XIV and XV (in instantaneous release) the mean concentration values after a source distance of a maximum of15 to 20 L_ei are already lower than in an area without obstacles.

In case of a continuous release, the measured mean UZD values in the range of 50 to 200 L_ee in the area types XIII to XV drop below the values measured in the area type III. However, during the entire heavy gas spread phase, those values are greater than the values measured in the area without obstacles.

Area map for dispersion area type XIII

Flat terrain. The dispersion takes place in a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 2 L_ei or 14 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 2 L_ei or 14 L_ee wide.
The source is located in the center of the canyon between two building gaps.

Area map for dispersion area type XIV

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 3 L_ei or 21 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 3 L_ei or 21 L_ee wide.
The source is located in the center of the canyon between two building gaps.

Area map for dispersion area type XV

Flat terrain. The dispersion takes place within a canyon of orthogonal wall interrupted by lateral gaps . It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 4 L_ei or 28 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 4 L_ei or 28 L_ee wide.
The source is located in the center of the canyon between two building gaps.

These dispersion areas can be used in principle for the same canyons as the dispersion area types X, XI and XII. However, the location of the source is moved upstream to the beginning of the building gap. A widening of the canyon and the building gaps leads to a reduction of the UZD values.

In instantaneous releases as well as in continuous releases, the mean UZD values measured in these areas are generally lower than the values measured in the dispersion area type III. In the dispersion area types XVI and XIII in instantaneous release, the mean UZD values are generally lower when there are no obstacles. This is also valid in case of continuous release for the dispersion area type XIII.
The mean UZD values are generally greater in the dispersion area type XI than in the dispersion area without obstacles. In the dispersion area type XVII the mean UZD values are at first lower than in the case without obstacles. Because of the reduced lateral dispersion of the cloud, the dilution proceeds slower than in the case without obstacles; and so the mean UZD values in the dispersion area type XVII from about 150 L_ee distance from the source, are greater than the values measured in the area type I.

Area map for dispersion area type XVI

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 2 L_ei or 14 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 2 L_ei or 14 L_ee wide.
The source is located in the center of the canyon at the beginning of a building gap.

Area map for dispersion area type XVII

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1.5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 3 L_ei or 21 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 3 L_ei or 21 L_ee wide.
The source is located in the center of the canyon at the beginning of a building gap.

Area map for dispersion area type XVIII

Flat terrain. The dispersion takes place within a canyon of orthogonal walls interrupted by lateral gaps. It is 1,5 L_ei (for instantaneous release) or 11 L_ee (for continuous release) high and 4 L_ei or 21 L_ee wide.
The lateral walls of the canyon consist of pieces which are 15 L_ei or 105 L_ee long and separated from each other by gaps which are 4 L_ei or 28 L_ee wide.
The source is located in the center of the canyon at the beginning of a building gap.

The dispersion area types XIX to XXI can be used for accidental releases, in which the dispersion takes place within an area of interrupted uniform buildings.

In instantaneous as well as in continuous release, the mean UZD values measured in these dispersion area types are lower than the values measured in the area without obstacles (area type I). The greater dilution is traced back to the greater mixing with ambient air caused by the buildings.
As it is evident from the concentration courses, a further interruption of the buildings leads to rising UZD values until finally the UZD values of obstacle free cases are reached.

Area map for dispersion area type XIX

Flat terrain. The dispersion takes place within an area of uniform buildings. The height of the buildings is 1 L_ei (for instantaneous release) or 11 L_ee (for continuous release). The lateral measurements of the buildings elements amount to 1 L_ei or 11 L_ee. The distance from each other is 2 L_ei or 21 L_ee, respectively.

Area map for dispersion area type XX

Flat terrain. The dispersion takes place within an area of uniform buildings. The height of the buildings is 1 L_ei (for instantaneous release) or 11 L_ee (for continuous release). The lateral measurements of the buildings elements amount to 1 L_ei or 11 L_ee. The distance from each other is 2,5 L_ei or 27 L_ee, respectively.

Area map for dispersion areas type XXI and XXII

Flat terrain. The dispersion takes place within an area of uniform buildings. The height of the buildings is 1 L_ei (for instantaneous release) or 11 L_ee (for continuous release). The lateral measurements of the buildings elements amount to 1 L_ei or 11 L_ee. The distance from each other is 3 L_ei or 32 L_ee, respectively.

Area map for dispersion area type XXIII

Flat terrain. The dispersion takes place within an area of uniform buildings. The height of the buildings is 1 L_ei (for instantaneous release) or 11 L_ee (for continuous release). The lateral measurements of the buildings elements amount to 1 L_ei or 11 L_ee. The distance from each other is 5 L_ei or 53 L_ee, respectively.

Area map for dispersion area type XXIV

Flat terrain. The dispersion takes place within an area of uniform buildings. The height of the buildings is 2 L_ei (for instantaneous release) or 21 L_ee (for continuous release). The lateral measurements of the buildings elements amount to 1 L_ei or 11 L_ee. The distance from each other is 3 L_ei or 32 L_ee, respectively.

Area map for dispersion area type XXV

Flat terrain. The dispersion takes places within an area of uniform buildings. The height of the buildings is 2 L_ei (for instantaneous release) or 21 L_ee (for continuous release). The lateral measurements of the building elements amount to 1 L_ei or 11 L_ee. The distance from each other is 4 L_ei or 43 L_ee, respectively.

* UZD (untere Zünddistanz) = lower flammability distance