Fire and Explosions

PHAST automatically generates the existing fires and explosions models as long as the material is flammable. This section presents a summary of the consequence calculation results for the study objects presented both in the form of tables and graphs. Each of the models is presented by two graphs and a table, each of which shows thermal or overpressure impacts from different study objects. The first graph shows thermal radiation or peak overpressure levels vs downwind distances, and the second graph presents their lethality radii.

Jet fires are mainly generated by any flammable containments leading to continuous releases (e.g. tank leak, pipe rupture, etc). PHAST will automatically calculate the jet fire impacts for given continuous models set by the user. The jet fire impact is thermal radiation (kW/m2) presented as table and graph such as a distance graph and fatality radii. Figure 5.4 shows the radiation levels (in kW/m2) for the jet fire as a function of distance downwind (in m) for two study objects and the weather category of 1.5/F. The radiation level is measured at the height of the release point used for the calculation of effects. Assuming that the orifice area in the tank (hole) is equal to the largest pipe diameter, the graph shows that the undesired events of tank leak dominate all of the system hazards. Furthermore, a larger inventory of hydrogen may results in a larger jet fire impact. The radiation levels remain constant for some downwind distance, and immediately drop to the lowest level.

Figure 5.5 shows the 1% lethality radii for the jet fire radiation impacts resulting from the tank leak events of the two hydrogen study objects. The graph shows that the fatal effect zone of a jet fire is presented as an ellipse centred on the release point. The fatality levels are calculated using the probit equation for thermal radiation impact from jet fires. The 1% fatality is equal to thermal radiation of 18.2 kW/m2 or probit level of 2.7 (see Table 4-10).

Table 5-26 shows the effect zones of the jet fire impacts for the seven hydrogen study objects for different fatality levels (of 1%, 10%, and 56%), and for the weather category of 1.5/F. The risk calculation, however, includes the jet fire impacts for all weather categories. The fatal effect-zone of a jet fire is modelled as an ellipse (4.5.5.4) centred at the release point (d=0). Axes a and b are the major and minor axes of the ellipse, and d is the relative offset of the ellipse centre from the release point defined as the ratio x/a where x is the distance from the release point to the ellipse centre. The effect distance (z) is calculated as the sum of downwind radius (a) and the downwind distance (x) from the release location. The table also shows that the study objects of GH2 pipeline did not reach the minimum fatality level (i.e. 1%).

Figure 5.4 Radiation vs distance for jet fire for different release events
Figure 5.5 Effect zones (1% fatality) of the jet fires for GH2 (solar) and LH2 (CHP)

4.4.2.2 Fireball

Fireball is mainly generated from any flammable (e.g. hydrogen) containment leading to instantaneous releases (e.g. tank rupture). PHAST calculates a wide range of thermal radiation impacts (kW/m2) resulted from a fireball. The fireball impacts are presented both in tables and graphs such as a distance graph, fatality radii, and so on. The distance graph shows the radiation level for the fireball as a function of the downwind distance. The radiation level is measured at the height of the release point used for the effect calculations. Figure 5.6 shows the radiation levels versus distance for fireballs for two study objects only and for all weathers. The fifth object (LH2 storage at CHP) gives greater fireball impact than the first object (GH2 storage at production plant). The radiation levels dramatically decrease with an increase of the distance from the release location.

Figure 5.6 Radiation vs distance of the fireball for the two hydrogen study objects

Effect zones of the fireball are presented as a circle or ellipse centred at the release point, and weather independence. Figure 5.7 shows the radii or ellipses for 1% fatalities resulting from fireball radiation. It plots the fatality levels resulting from fireball calculated using the probit equation 4-8. This measure takes fireball duration (t) into account in calculating the potential fatality effects. Therefore, fatality level (%) from the fireball is proportional to different values of thermal radiation (kW/m2), and depends on the fireball duration. For example, in Table 5-27 it shows that 1% fatality (probit value of 2.7) proportional to different intensity levels.

Table 5-27 presents the fireball impacts for the all study objects, for different fatality levels (of 1%, 10%, and 56%), and for all weather categories. The effect distance (z) of fireball is equal to its downwind radius, because the fireball centre is in the release point and weather independent. The seventh object (GH2 pipeline) is not assumed to produce a fireball, because the release from the object is classified as continuous.

Table 5-26 Thermal impacts of jet fires^ for the hydrogen plants (Weather 1.5/F)

Study

Consequence

Units

Fatality level (probit)

Objects

1%(2.7)

10%(3.7)

56%(5.1)

Intensity level (I)

kW/m2

18.2

24.7

37.5

Exposure time (t)

s

20

20

20

Downwind semi-axis (a)

m

22.6

21.4

19.6

1 (Solar)

Crosswind semi-axis (b)

m

12.5

9.5

6.4

Offset ratio (d)

-

0.0

0.0

0.0

Effect distance (z)

m

22.6

21.4

19.6

Downwind semi-axis (a)

m

114.9

110.6

105.1

2 (Depot)

Crosswind semi-axis (b)

m

59.2

44.9

30.6

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

114.9

110.6

105.1

Downwind semi-axis (a)

m

73.1

70.2

66.3

3 (FS)

Crosswind semi-axis (b)

m

34.8

26.1

17.4

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

73.1

70.2

66.3

Downwind semi-axis (a)

m

26.7

25.3

23.2

4 (Car)

Crosswind semi-axis (b)

m

11.0

8.2

5.5

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

26.7

25.3

23.2

Downwind semi-axis (a)

m

94.3

70.1

66.2

5 (CHP)

Crosswind semi-axis (b)

m

47.4

26.1

17.4

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

94.3

70.1

66.2

Downwind semi-axis (a)

m

73.0

70.2

66.2

6 (Truck)

Crosswind semi-axis (b)

m

34.7

26.1

17.4

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

73.0

70.2

66.2

Downwind semi-axis (a)

m

n.r.

n.r.

n.r.

7

Crosswind semi-axis (b)

m

n.r.

n.r.

n.r.

(Pipeline)

Offset Ratio (d)

-

n.r.

n.r.

n.r.

Effect Distance (z)

m

n.r.

n.r.

n.r.

Notes: n.r. = not reached; probit uses exposure time (t) = 20 s (for flammable materials)

Notes: n.r. = not reached; probit uses exposure time (t) = 20 s (for flammable materials)

Figure 5.7 Effect zones (1% fatality) of the fireball for the two hydrogen study objects

4.4.2.3 Flash Fire

Flash fires are treated in different ways depending on the types of release. Flash fires resulting from instantaneous releases (e.g. tank rupture) are represented as circular cloud indicating the radius of the LFL fraction (2%) to finish (see section 4.5.5.2). The circle starts centred at the release point and then proceeds to drift downwind. For continuous releases the flash fire effect zone is taken to be the cloud boundary to the LFL fraction represented as an ellipse. There is also the possibility that the ellipse is defined as a 'half-ellipse' rather than the full shape. Figure 5.8 shows the maximum area covered by the flash fire envelope, i.e. the area swept out by the flash fire footprint, through all wind directions. The envelope is given for LFL (4%) and half the LFL (2%), and is at the height for calculation of effects.

Table 5-27 Thermal impact levels of the fireball for the hydrogen plants (all weathers)

Study

Consequence

Units

Fatality levels (probit)

Objects

parameters

1%(2.7)

10%(3.7)

56%(5.1)

Fireball duration (t)

s

3.4

3.4

3.4

1 (Solar)

Intensity level (I)

kW/m2

68.5

92.8

140.8

Effect Distance (z)

m

42.9

35.4

26.3

Fireball duration (t)

s

11.4

11.4

11.4

2 (Depot)

Intensity level (I)

kW/m2

27.8

37.8

57.3

Effect Distance (z)

m

217.6

185.3

61.1

Fireball duration (t)

s

4.2

4.2

4.2

3 (FS)

Intensity level (I)

kW/m2

59

80.2

121.6

Effect Distance (z)

m

56.3

46.7

35.4

Fireball duration (t)

s

0.8

0.8

0.8

4 (Car)

Intensity level (I)

kW/m2

200.4

272.2

412.7

Effect Distance (z)

m

4.9

3.4

n.r.

Fireball duration (t)

s

7.2

7.2

7.2

5 (CHP)

Intensity level (I)

kW/m2

39.0

53.0

80.4

Effect Distance (z)

m

119.1

101.0

78.7

Fireball duration (t)

s

7.1

7.1

7.1

6 (Truck)

Intensity level (I)

kW/m2

39.5

53.6

81.4

Effect Distance (z)

m

116.5

98.8

76.9

Notes: n.r. = not reached; effect distance (z)=downwind distance; exposure time (t)=fireball duration

Notes: n.r. = not reached; effect distance (z)=downwind distance; exposure time (t)=fireball duration

Flashfire Lfl Offset
Figure 5.8 Effect zones of the flash fires for the two study objects

Table 5-28 shows effect distances resulting from flash fires for the all hydrogen study objects. They are calculated for the LFL fraction (2%), for different loss of containment events (A-F) and weather 1.5/F. Loss of containment A (except for the object no.7) presents a flash fire resulting from an instantaneous release. While the rests (B-F) presents flash fires resulting from continuous releases. The flash fire description therefore gives the size and downwind distance of the cloud at several time-steps during the time when it is developing to its fullest extent.

Table 5-28 Thermal impact of flash fire (0.02 fraction) for the hydrogen plants

Study

Consequence

Unit

Loss of containment events

objects

A

B

C

D

E

F

LFL fraction radius

m

27.7

46.2

2.7

8.2

8.2

-

1 (Solar)

Downwind distance

m

10.2

0.0

0.0

0.0

0.0

-

Effect distance

m

37.9

46.2

2.7

8.2

8.2

-

LFL fraction radius

m

2483.1

279.3

15.9

15.5

17.6

48.4

2 (Depot)

Downwind distance

m

435.2

0.0

0.0

0.0

0.0

0.0

Effect Distance

m

2918.3

279.3

15.9

15.5

17.6

48.4

LFL fraction radius

m

136.0

184.4

6.0

15.5

18.0

26.0

3 (FS)

Downwind distance

m

71.0

0.0

0.0

0.0

0.0

0.0

Effect Distance

m

207.0

184.4

6.0

15.5

18.0

26.0

LFL fraction radius

m

24.4

84.8

2.3

3.0

3.1

3.6

4 (Car)

Downwind distance

m

11.5

0.0

0.0

0.0

0.0

0.0

Effect Distance

m

35.9

84.8

2.3

3.0

3.1

3.6

LFL fraction radius

m

1167.1

2347.0

15.9

15.5

17.6

27.9

5 (CHP)

Downwind distance

m

358.0

0.0

0.0

0.0

0.0

0.0

Effect Distance

m

1525.1

2347.0

15.9

15.5

17.6

27.9

LFL fraction radius

m

2739.3

184.4

13.0

15.5

17.6

120.3

6. (Truck)

Downwind distance

m

130.0

0.0

0.0

0.0

0.0

0.0

Effect Distance

m

2869.5

184.4

13.0

15.5

17.6

120.3

(Pipeline)

LFL fraction radius

m

7.9

7.3

-

-

-

-

Downwind distance Effect Distance

m m

0.0 7.9

0.0 7.3

-

-

-

-

Notes: For 1-6: A=tank rupture; B=tank leak; C=relief valve; D=rupture disc; E=vapour line, F=liquid line For 7: A =pipeline rupture; B=Hole in the pipeline

Notes: For 1-6: A=tank rupture; B=tank leak; C=relief valve; D=rupture disc; E=vapour line, F=liquid line For 7: A =pipeline rupture; B=Hole in the pipeline

Figure 5.9 Early explosion overpressure vs distance of the two hydrogen objects

4.4.2.4 Early Explosion

An early explosion may be generated from any instantaneous release. It occurs at the beginning of the release, before the cloud has started to disperse. The main consequence of the explosion is overpressure (bar). Fig. 5.9 shows the early explosion overpressure vs distance for two study objects. The fifth object (LH2 at CHP) shows greater impacts that than of the first object (GH2 at production plant). Effect zones of the explosion are presented as a circle or ellipse centred at the release point, and independent of the weather conditions. Fig. 5.10 shows the effect zones in terms of overpressures radii of the early explosion for 0.021 bar (about 0.01% fatality). The fatality levels correspond to different explosion damage levels is shown in Table 4-14. For example, 1% fatality corresponds to peak overpressure of 0.14 bar, and 10% fatality correspond to 0.21 bar. Table 5-30 shows the early explosion impacts calculated by using the TNT model (in PHAST) for different fatality levels, and for the all study objects.

Figure 5.10 Effect zone (0.01% fatality) of the early explosion for the two study objects
Table 5-29 Early explosion impacts of the hydrogen objects

Study Objects

Consequence parameters

Units

Fatality levels (%)

0.01

1

10

1 (Solar)

Effect Distance (z)

m

334.4

86.7

67.0

2 (Depot)

Effect Distance (z)

m

1149.3

297.6

230.3

3 (FS)

Effect Distance (z)

m

421.3

109

84.4

4 (Car)

Effect Distance (z)

m

82.5

21.4

16.5

5 (CHP)

Effect Distance (z)

m

732.1

189.6

146.7

6 (Truck)

Effect Distance (z)

m

720.0

186.5

144.3

7 (Pipeline)

Effect Distance (z)

m

-

-

-

Notes: 0.01%=0.02 bar; 1% = 0.1379 bar; 10% = 0.2068 bar (See Section 4.5.6.2.2) 4.4.2.5 Late Explosion (VCE)

Notes: 0.01%=0.02 bar; 1% = 0.1379 bar; 10% = 0.2068 bar (See Section 4.5.6.2.2) 4.4.2.5 Late Explosion (VCE)

Late explosion or vapour cloud explosion (VCE) may occur if the vapour cloud is ignited before it is diluted bellow its LFL (4%). The centre of the explosion of the VCE is the cloud centre at the point downwind from the release centre at the moment of ignition. Fig. 5.11 shows the overpressure (bar) as a function of distance downwind (m) of the late explosion (VCE) resulting from different loss of containments events (LOCs) of the two objects. There is a separate overpressure curve for each release event with different profiles and explosion centre location. Overpressure resulting from the tank ruptures (both GH2 and LH2) increase instantaneously to the maximum peak overpressure and then decrease with the increase of distance. On other hand, the continuous releases (e.g. leak) require a certain time before peak overpressure reached, after that it begins to decrease again to zero.

Figure 5.11 Peak overpressure vs distance of the late explosion

Effect zones of the late explosion (VCE) are calculated similar to the early explosion, except that the explosion centre is not at the centre of the release point (see 4.5.5.1). It is modelled as two concentric circles displaced from the release point. The overpressure radii of the late explosion for the time when the leading edge (for a continuous release) or the cloud centre (for an instantaneous release) reaches a given distance downwind is given in Fig. 5.12. This figure shows that the effect zones for the study objects GH2 (solar) and LH2 (CHP) at 0.01% fatality (0.02 bar) are 341.2 m and 741 m, respectively. Meanwhile, the explosion centre of the LH2 leak events is located far away from the release centre, but it results in a small zone.

Figure 5.12 Effect zones (0.01% fatality) of late explosion for the two study objects

The effect distances for 1% and 10% fatality resulting from late explosion for different loss of containment events (A-F) of the all study objects, and for the weather category 1.5/F are presented in the Table 5-30. Assume that the fatality is constant with one value inside the central zone and constant with another value in the annulus formed by the inner and outer circles.

Table 5-30 Late explosion impacts for the hydrogen objects _(Weather 1.5/F)

Study

Late explosion

Unit

A

B

E

F

object

1%

10%

1%

10%

1%

10%

1%

10%

Solar

Overpressure radius

m

80.2

62.1

28.1

21.8

19.6

15.1

-

-

Downwind distance

m

30.0

30.0

60.0

60.0

10.0

10.0

-

-

Effect distance

m

110.2

92.1

88.1

81.8

29.6

25.1

-

-

Overpressure radius

m

26.3

20.3

146.1

113.1

28.6

22.1

68.9

53.3

2.

Downwind distance

m

560.0

560.0

450.0

450.0

40.0

40.0

110.0

110.0

Depot

Effect Distance

m

586.3

580.3

596.1

563.1

68.6

62.1

178.9

163.3

o

Overpressure radius

m

78.3

60.6

54.1

42.0

28.6

22.1

40.6

31.4

FS

Downwind distance

m

70.0

70.0

180.0

180.0

40.0

40.0

60.0

60.0

Effect Distance

m

148.3

130.6

234.1

222.0

68.6

62.1

100.6

91.4

4

Overpressure radius

m

17.0

13.2

7.9

6.1

-

-

-

-

Car

Downwind distance

m

10.0

10.0

70.0

70.0

-

-

-

-

Effect Distance

m

27.0

23.2

77.9

76.1

-

-

-

-

c

Overpressure radius

m

134.9

104.4

94.0

72.8

28.6

22.1

43.4

33.6

CHP

Downwind distance

m

130.0

130.0

250.0

250.0

40.0

40.0

60.0

60.0

Effect Distance

m

164.9

134.4

344.0

322.8

68.6

62.1

103.4

93.6

R

Overpressure radius

m

60.5

46.6

21.3

16.5

130.0

100.0

28.6

22.0

Truck

Downwind distance

m

160.0

160.0

20.0

20.0

130.0

130.0

40.0

40.0

Effect Distance

m

220.5

206.6

41.3

36.5

260.0

230.0

68.6

62.0

Pipe

Overpressure radius

m

18.5

14.3

17.5

13.6

-

-

-

-

Downwind distance

m

10.0

10.0

10.0

20.0

-

-

-

-

Effect Distance

m

28.5

24.3

27.5

33.6

-

-

-

-

Notes: For 1-6: A=tank rupture; B=tank leak; C=relief valve; D=rupture disc; E=vapour line, F=liquid line

For 7: A =pipeline rupture; B=Hole in the pipeline

Notes: For 1-6: A=tank rupture; B=tank leak; C=relief valve; D=rupture disc; E=vapour line, F=liquid line

For 7: A =pipeline rupture; B=Hole in the pipeline

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