Risk Calculation

The risk associated with the hydrogen study objects was calculated by combining the consequence and frequency analysis results, using the risk calculation model, described in Section 4.6.2. The model assumed that risk of each event can be treated independently from other events. Integration of the risk from all possible events can, therefore, be built up event by event and this is one of the principles of the model.

Table 5-31 illustrates an example to calculate the fireball risks impacted on the population with the model described in section 4.6.2 (analytical approach). Inputs of the model mainly consist of consequence and frequency analysis results. Firstly, effect zone area of the outcome is calculated based on the fire and explosion models described in section 4.5.5. Each accident outcome has a different effect zone area which is calculated as the area of the respective shapes of the outcome. For example, a fireball is modelled as a circle with radius (r), where r is equal to downwind (a) or crosswind (b), and centred at the release centre. So that the factored area (Af) is equal to the effect zone area (A=p*r2) multiplied with the associated fatality level (%). Number of fatality for given outcome, rate of death, and "Okrent number" are calculated using eq. 4-15, 4-16, and 4-17 respectively. The array sum can be calculated as factored area (Af) multiplied with frequency (F) and divided by the defined grid area. The average value of the Germany population density (i.e. 0.00023 people per square meter) was used in the study. It is approximately 231 inhabitants per square kilometre of land [176]. The table shows that the fatality number (N values) may be impacted by the fireball are 0, 0, 1 people, for the fatality level of 1%, 10%, and 56%, respectively.

In order to obtain the overall risks of a hydrogen study object, the risks resulting from other considered accident outcomes (such as jet fire, flash fire, early explosion, late explosion) have been calculated in a similar manner. Furthermore, the calculations were repeated for different weather categories (i.e. 1.5/F, 1.5/D. 5.0/D), and for all scenarios (undesired events) considered. Table 5-32 shows the overall risk of the hydrogen fuelling station. The risk calculation included six different release event types (i.e. tank rupture, tank leak, relief valve open, rupture disk break, liquid line rupture, and vapour line rupture). The same outcomes (i.e. continuous flash fire, jet fire, late explosion) were considered for each of the release events. Additional incident outcomes such as fireball and early explosion were considered for the tank rupture event. The mean value of the overall risk for death of the hydrogen fuelling station is 9.6 x 10-5 per year. These procedures were repeated for all the study objects, the results are presented in Appendix H.

Table 5-31 Analytical risk calculations of the fireball impacts on population

Parameters

Units

Lethality Level

1%

10%

56%

Intensity Level

kW/m2

59.0

80.2

121.6

View Factor

0.15

0.2

0.3

Probit Level

-

2.7

3.7

5.1

Downwind semi-axis (a)

m

56.3

46.7

35.4

Crosswind semi-axis (b)

m

56.3

46.7

35.4

Offset Ratio (d)

-

0.0

0.0

0.0

Effect Distance (z)

m

56.3

46.7

35.4

Frequency (F)

per year

1.1E-08

1.1E-08

1.1E-08

Grid cell size (g)

m

10.0

10.0

10.0

Population density (N/mA2)

Pop./m2

0.00023

0.00023

0.00023

Effect zone area (A)

m2

9950.2

6854.0

3933.0

Factored area(Af)

m2

99.5

685.4

2202.5

Number of fatality (N)

people

0

0

1

Array sum(/yr)

per year

1.1E-08

7.4E-08

2.4E-07

Rate of death(/yr)

per year

4.0E-09

2.7E-08

8.8E-08

Okrent(/yr)

per year

1.0E-10

7.0E-10

2.3E-09

Table 5-32 The overall risk of the hydrogen filling station

Accident outcome

Weath er

Fatali

Frequency(/yr)

Effect

Fatality (N)

LOCs

Level

5%

50%

Mean

95%

Distance (m)

1.5/F

1% 10%

8.4E-08 8.4E-08

6.1E-07 6.1E-07

1.3E-06 1.3E-06

4.5E-06 4.5E-06

100.6 91.4

0 0

Late

1.5/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

103.0

0

Liquid

Explosion

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

93.2

0

line

5.0/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

93.0

0

rupture

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

85.6

0

Flash Fire

1.5/F

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

60.5

1

1.5/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

48.0

1

5.0/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

64.0

1

1.5/F

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

54.4

0

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

21.5

0

Late

1.5/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

54.0

0

Relief valve

Explosion

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

21.3

0

5.0/D

1% 10%

8.4E-08 8.4E-08

6.1E-07 6.1E-07

1.3E-06 1.3E-06

4.5E-06 4.5E-06

43.2 19.0

0 0

Flash Fire

1.5/F

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

14.4

0

1.5/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

14.0

0

5.0/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

16.0

0

1.5/F

1% 10%

8.4E-08 8.4E-08

6.1E-07 6.1E-07

1.3E-06 1.3E-06

4.5E-06 4.5E-06

56.4 50.4

0 0

Late

1.5/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

57.8

0

Rupture disk

Explosion

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

51.5

0

5.0/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

51.0

0

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

46.3

0

Flash Fire

1.5/F

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

37.6

1

1.5/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

32.3

0

5.0/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

39.4

1

1.5/F

1% 10%

8.4E-08 8.4E-08

6.1E-07 6.1E-07

1.3E-06 1.3E-06

4.5E-06 4.5E-06

234.1 222.0

0 1

Late

1.5/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

320.0

0

Explosion

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

304.0

1

5.0/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

331.5

0

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

313.0

1

1%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

148.4

0

1.5/F

10%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

143.2

0

Tank

56%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

136.5

1

leak

1%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

148.4

0

Jet Fire

1.5/D

10%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

143.2

0

56%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

136.5

1

1%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

118.3

0

5.0/D

10%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

113.3

0

56%

2.3E-05

1.7E-04

3.6E-04

1.2E-03

107.2

1

Flash Fire

1.5/F

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

253.4

22

1.5/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

263.0

24

5.0/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

238.0

20

Vapour line

1.5/F

1% 10%

8.4E-08 8.4E-08

6.1E-07 6.1E-07

1.3E-06 1.3E-06

4.5E-06 4.5E-06

68.6 62.1

0 0

rupture

Late

1.5/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

69.3

0

Explosion

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

62.7

0

5.0/D

1%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

62.5

0

10%

8.4E-08

6.1E-07

1.3E-06

4.5E-06

57.4

0

Flash Fire

1.5/F

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

42.0

1

1.5/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

55.0

2

5.0/D

60%

3.4E-07

2.4E-06

5.1E-06

1.8E-05

26.0

1

1.5/F

1% 10%

2.5E-12 2.5E-12

1.8E-11 1.8E-11

3.7E-11 3.7E-11

1.3E-10 1.3E-10

148.3 130.6

0 1

Late

1.5/D

1%

2.5E-12

1.8E-11

3.7E-11

1.3E-10

144.0

0

Explosion

10%

2.5E-12

1.8E-11

3.7E-11

1.3E-10

125.4

1

5.0/D

1%

2.5E-12

1.8E-11

3.7E-11

1.3E-10

224.5

0

10%

2.5E-12

1.8E-11

3.7E-11

1.3E-10

212.2

1

Tank

Early

1%

5.1E-08

3.7E-07

7.7E-07

2.7E-06

109.0

0

Rupture

Explosion

10%

5.1E-08

3.7E-07

7.7E-07

2.7E-06

84.4

0

1%

2.0E-07

1.5E-06

3.1E-06

1.1E-05

56.3

0

Fireball

-

10%

2.0E-07

1.5E-06

3.1E-06

1.1E-05

46.7

0

60%

2.0E-07

1.5E-06

3.1E-06

1.1E-05

35.4

1

Flash Fire

1.5/F

60%

9.8E-12

7.1E-11

1.5E-10

5.2E-10

263.0

6

1.5/D

60%

9.8E-12

7.1E-11

1.5E-10

5.2E-10

218.0

5

5.0/D

60%

9.8E-12

7.1E-11

1.5E-10

5.2E-10

543.0

32

Overall risk

3.3E-03

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