Risk Presentation

Two risk measures were considered to present the risk associated with the hydrogen study objects, i.e. individual and societal risk (F-N curve), as described in section 4.6.1.

5.5.2.1 Individual Risk (IR)

The IR of the hydrogen study objects are presented as risk profiles. To create a risk profile, the triplets of the overall risk in Table 5-32 must be transformed into risk profiles and plotted by means of the CCDF, as described in section 4.6.2.2. The risk is expressed as individual risk depending on distance from the objects.

Figure 5.13 Individual risk profiles of the hydrogen cycle

Fig. 5.13 shows an individual risk profile for the hydrogen study objects, with the capacity of 6 - 16250 kg of hydrogen. Failure of such objects leads to fatal consequences from a distance of 35 m (e.g. pipeline) up to a distance of 4374 m (e.g. depot). It seems that the effect distance is proportional to the hydrogen capacity. The consequence calculation result, however, shows that the risks of the GH2 (e.g. production plant) have smaller distance compared with the one of LH2 (e.g. depot). The figure also shows that the hydrogen objects have a higher risk at a shorter distance than that at the larger distance from the object. The overall IR of the hydrogen objects is in the ranges of 10-2 and 10-4 per year. The production plant (GH2) has the lowest risks levels (2.3 x 10-4 /year). The risks are sharply decreasing with the increase of the distance. For example, risk of the LH2 at fuelling station decreased from 3.6 x 10-3 /year to about 10-10 at a distance of 322 m.

Figure 5.14 Societal risks (FN-Curves) of the hydrogen study objects

All of the information required for individual risk calculation, as well as information on the population surrounding the facility or along the transportation routes are required for the societal risk calculation. By using the procedure described in section 4.6.2.2, the societal risks (F-N curves) for the hydrogen study objects are presented in Fig. 5.14. It is connected to the hydrogen plants, with the capacity of 6 - 16250 kg of hydrogen. Failure of such plants leads to maximum fatality number of about 2 people (for GH2 pipeline) up to 2100 people (for LH2 at depot). These fatalities are connected to the risk of 10-9 /year. The GH2 plants (e.g. production plant and pipeline) give the lowest risk compared to the one of LH2 plants.

The figure also shows that the hydrogen objects have a lower societal risk than that of individual risk. For example, the individual risk (risk to 1 person) of the road tanker is about 10-4/yr, and the societal risk drops to 10-6 with correspond to the fatality number of about 20 people. The overall risk of the hydrogen study objects are in the ranges of 10-3 and 10-5 /year.

5.6 RISK EVALUATION

5.6.1 Summary of the Numerical Results

5.6.1.1 The Frequency

Table 5-33 shows that the overall average of the hydrogen release frequencies of the study objects is about 1.9 x 10-3 per year (once per 517 years). Based on frequency calculation results of the study objects, GH2 storage has a lower accident frequency compared with the

LH2 storage. The reason is that the LH2 storage introduces more potential hazards than the one in GH2 (i.e. cryogenic liquid hazards). All these may contribute to modes of potential failure and result in great contributions to the overall release frequency.

Table 5-33 Overall release frequencies of the hyc

rogen stuc

y objects

No

Plant

Storage types

5%

50%

Mean

95%

K-95

Source

3

Solar H2 plant

gh2

1.8E-06

1.5E-05

3.6E-05

1.3E-04

8.6

FTA

4

H2 Fuelling Station

lh2

4.7E-05

3.4E-04

7.1E-04

2.5E-03

7.3

FTA

5

H2 Fuel Cell - CHP

lh2

5.1E-06

5.2E-05

1.4E-04

5.4E-04

7.3

FTA

6

H2 Depot

lh2

5.6E-06

4.8E-05

1.2E-04

4.6E-04

9.6

FTA

7

H2 Private Cars

LH2

-

-

7.1E-04

-

-

Data

8

H2 Road Tanker

lh2

-

-

6.9E-05

-

-

Data

9

H2 Pipeline

gh2

-

-

1.5E-04

-

-

Data

Overall

7.5E-04

1.7E-03

1.9E-03

3.9E-03

2.3

The loss of containment events (LOCs) of hydrogen storages and transportations considered in the QRA study include: continuous and instantaneous release. Frequency analysis showed that the overall average contributions of the continuous dominated to about 94% of the scenario and only 6% for the instantaneous. It means that the probability of occurrence per year of the instantaneous release is very low. The instantaneous release of hydrogen mainly results from a catastrophic failure of tank storage (e.g. tank rupture), and release the all inventory contents. Tank rupture is mainly caused by tank overpressure (with the contribution of more than 50%), it is followed by external events, and spontaneous events. In case of LH2, there is an additional incident that may contribute to the tank rupture, i.e. tank under-pressure with the contribution of about 30%. All hydrogen storages are equipped with redundant safety protections against tank overpressure, such as pressure relief valves and rupture discs. The tank overpressure may lead to tank rupture, if all pressure relief devices fail close. The tank overpressure is mainly caused by tank overfilling, loss of vacuum (in case of LH2 only), external fire, internal explosion, overheating of the pressure building circuits (in case of LH2 only), and so on.

The continuous release gave the greatest contribution to the loss of containment event in the hydrogen study objects. It is mainly caused by pipelines rupture and tank leakage. Although the tank leakage event may be considered as a rare event but it may result severe damage to environment. In case of LH2 storage, an additional release may be resulted from pressure building circuit (PBC) failure.

Fires and explosions are the two incident outcomes which may result from a hydrogen release when ignition sources exist. The frequency analysis showed that the fire outcomes are mostly dominant. They account for about 60%, only about 5% result in explosion, and the rest (35%) has no effect (harmless) on the environment. It can be understood that an explosion requires certain conditions such as confined area. high ignition energy, and so on.

Several errors may exist during the frequency analysis include: (1) incorrect estimation of probability or frequencies of the basic events, (2) erroneous assumption of independence of bottom events, and so on.

5.6.1.2 The Consequence

The loss of containment event of the study objects results in different types of consequences, such as jet fires, fireballs, explosions, and so on. Each of the outcomes was modelled for different shapes and sizes that is required for the impact calculations. Circle and ellipse are the shapes considered to calculate impact zones resulting from fires and explosions.

The major hazards associated with hydrogen are fires and explosions, and in the event of contact with the liquid or cold boil off vapour, frostbite and burns. The study considers fire and explosion hazards because they may result in fatalities in the population around the installation. In general, the fire and explosion consequences are proportional to their inventory capacity. A larger hydrogen inventory (in kg) may result in larger impacts.

In general, human fatalities of the hydrogen consequence may be estimated by using of probit equations. Fatality level (%) of fire outcomes is proportional to thermal radiation (kW/m2), while the peak overpressure (bar) for the explosion. The existing the probit equations for explosion could not be used directly to estimate the human fatalities, because they showed small impacts. A conservative approach has been taken to estimate fatalities for given explosion, instead of the probit equations.

Errors which may arise in consequences analyses include: (1) imperfections and oversimplifications in the physical models as representations of real behaviour, (2) error in the parameters of the physical models, (3) error due to simplification in the computing, and so on.

5.6.1.3 The Overall Risk

The societal risk results as a measure of the risk that the events pose to the local population expressed by frequency F as a function of fatalities N, which is then plotted to give the F-N curve. The frequencies for given values of N can be summed for all outcomes and events to give the overall societal risk. The overall risk of the hydrogen study objects is 8.5 x 10-3/ year (once in 118 years) shown in Table 5-36. The most contributor to the overall risk is LH2 storage at fuelling station (accounted for 39%), followed by LH2 storage in private car (accounted for 35%), LH2 at CHP plant (7.7%), LH2 at depot (6.5%), GH2 pipeline (5%), LH2 tanker truck (4.4%), and GH2 at production plant (2.7%). Figure 5.17 shows the overall risk for the hydrogen cycles.

Table 5-34 The overall individual risk of the hydrogen study objects

Study Objects

5%

50%

Mean

95%

GH2 at production plant

1.1E-05

9.5E-05

2.3E-04

8.5E-04

LH2 at depot

2.3E-05

2.2E-04

5.5E-04

2.1E-03

LH2 at fuelling station

2.2E-04

1.6E-03

3.3E-03

1.1E-02

LH2 at CHP plant

2.3E-05

2.4E-04

6.5E-04

2.5E-03

LH2 in private car

-

-

3.0E-03

-

LH2 tanker truck

-

-

3.7E-04

-

GH2 pipeline

-

-

4.1E-04

-

Overall risk

9.5E-4

3.5E-03

8.5E-03

1.3E-02

5.6.2 Evaluation Against the Risk Criteria

As described in section 4.6.3, the study uses the ALARP risk acceptance criteria proposed by the EIHP2 (European Integrated Hydrogen Projects). Figure 5.15 shows that, according to the Dutch regulations (Dutch National Environmental Policy Plan, 1989), as well as U.K. standards (Health and Safety Commission, 1991), the individual risk for the hydrogen objects (both hydrogen storages and transportations) run almost entirely in the unacceptability zone, being higher than 1 x 10-6 /year (for the Dutch regulations) or 1 x 10-4 /year (for the U.K standards) or where the measures to reduce the risk must be implemented.

The figure also shows that the societal risk level appears globally lower than the individual one. In fact, also the curves relevant to the hydrogen objects, fall well in the acceptable of the UK ALARP zone (dotted lines). However, assuming the limits proposed by Dutch regulations (solid lines), different in slope and more severe than the U.K. ones, most of the curves fall within the ALARA zone. These mean that the hydrogen storages and transports may be accepted for the public. Should the plants be implemented for the public, the risk must be reduced as far as reasonable and practicable, typically subject to cost benefit analysis. Meanwhile, hydrogen production plant (GH2) and pipeline (GH2) fall well in the acceptable zones of the ALARP as well as the ALARA.

Alarp Meaning
Figure 5.15 F-N curve of the hydrogen cycles with the ALARP criteria 5.6.3 Comparisons with the LPG study

5.6.3.1 LPG Study Objects

Propane (C3H8) is a very common fuel, particularly in rural areas where it is used for crop drying, cooking, heating, and as a motor vehicle fuel. Propane is also the main constituent of "bottle gas" or LPG- Liquified Petroleum Gas. LPG may also contain butane, propylene, or butylene. These are gases at standard conditions, but become liquids at room temperature at moderate pressures. At 38°C, propane liquifies at about 13.8 bar, while butane remains a liquid at pressures above 4.14 bar at this temperature. LPG can therefore be handled as a liquid at room temperature with moderate pressure cylinders. LPG is primarily a domestic fuel, produced as a by-product from natural gas processing and crude oil refining.

Table 5-35 Dimension and capacities of the

lPG study objects [187]

Specifications

Storage

Transport

Depot

Fuelling Station

Road Tanker

Pipeline

Capacity (m3) or (m3/h)

165

20

45

225

Capacity (kg)

86576

10494

22300

-

Tank type

Cylindrical

Cylindrical

Cylindrical

Length (m)

21

7

11

n.a.

diameter (m)

3.2

2.1

2.3

0.3

liquid line (m)

0.1

0.08

0.08

-

Vapour line (m)

0.1

0.05

0.05

-

The risks of the hydrogen study objects were compared with the LPG study objects given in the LPG study [187]. The LPG study describes the present and future activities relating to LPG in the Netherlands, which include of storage and transport systems. The study took four LPG objects that have similar size and function to the hydrogen study. Assuming that the LPG truck and LPG pipeline operate on the similar routes as the one of the LH2 truck and GH2 pipeline, respectively. It also assumed that LPG is pure Propane with the liquid density of 575 kg/m3 (see Appendix A). They include LPG storage at depot, LPG filling station, LPG road tanker, and LPG pipeline, as shown in Table 5-35.

5.6.3.2 The Frequency Comparison

Frequencies of the LPG objects were estimated using the same procedure given for the hydrogen study (i.e. given in section 4.4). Most of the expected frequency, however, was taken from the TNO study [187], as shown in Table 5-36. Expected frequency of the LPG truck and LPG pipeline were estimated from the truck accident rate and pipeline failure data given in [187]. Assuming that the LPG truck and pipeline operate on similar routes as the one for the LH2 truck and pipeline, the expected frequency is calculated using eq. 4-7 and 4-8, respectively. The result is shown in Table 5-36. A brief comparison between the LPG and hydrogen study objects show that the overall incident frequency of the hydrogen study objects is bit higher lower than of the LPG. The hydrogen objects frequency is 1.0 x 10-3 /year (once per 991 years), while the LPG is 9.3 x 10-4 /year (once per 1077 years).

Table 5-37 shows accident outcome frequencies of the LPG study objects. It can be seen that the fire mostly dominates the accident outcomes (accounting for 23%). Only 2% of the accident outcome may lead to explosions and the remaining (75%) of the accidents have no effect on the population

Table 5-36 Expected Frequency of the LPG study objects considered

No

(/yr)

Source of Justification

1

LPG depot

2.2E-04

TNO (1983)

2

LPG filling station

5.4E-04

TNO (1983)

3

LPG Truck

6.9E-05

1.6E-7/veh-km (TNO), take similar route as for the LH 2 truck

4

LPG pipeline

1.1E-04

1.0E-4/km-yr (TNO), take similar route as for the GH2 pipeline

Total

9.3E-04

5.6.3.3 The Consequence Comparison

The consequences of the LPG study objects have been assessed using the same procedure given for the hydrogen study (i.e. given in section 4.5). This assessment includes the impacts of fireball, flash fire, explosions, etc to human. A brief consequence comparison between hydrogen and LPG study is presented in Fig. 5.16 and Fig. 5.17. The consequences of the LH2 filling station were compared with the LPG filling station. Due to the fact that LPG has higher density per volume the LPG objects are simulated for different sizes. The LH2 fuelling station (tank capacity of 12m3) was compared with the various capacities of LPG fuelling station (i.e. 20m3, 12m3, and 2m3). The LPG fuelling station with the tank capacity of 20m3 is a modern above-ground installation in the Netherlands [187]. Two other capacities were considered for the same tank geometric volume (12m3) and the same tank inventory in kg (2m3) with the LH2 fuelling station.

Table 5-37 Accident outcome frequency of the LPG study objects

Accident Outcomes

Frequency (/yr)

LOCs

Depot

Filling station

Truck Route 1

Truck Route 2

Pipeline

Early explosion

9.6E-08

2.3E-06

4.6E-06

3.5E-07

-

Fireball

6.4E-08

1.5E-06

3.1E-06

2.3E-07

-

Instantaneous.

Pool fire

7.7E-08

1.8E-06

3.7E-06

2.8E-07

-

VCE

5.8E-09

1.4E-07

2.8E-07

2.1E-08

-

Flash fire

3.8E-09

9.2E-08

1.8E-07

1.4E-08

-

Jet fire

2.2E-05

5.1E-05

4.5E-06

3.4E-07

6,8E-05

Continuous

Pool fire VCE

3.1E-05 2.3E-07

7.3E-05 5.5E-07

6.5E-06 4.8E-08

4.8E-07 3.6E-09

8.3E-06

Flash fire

1.6E-07

3.6E-07

3.2E-08

2.4E-09

2.2E-05

Harmless

1,6E-04

3.8E-04

4.1E-05

3.1E-06

7.5E-06

Total

2.2E-04

5.2E-04

6.4E-05

4.8E-06

1.1E-04

Table 5-38 Qualitative assessment of the hydrogen and LPG consequences

LH2 12m3

LPG 20m3

LPG 12m3

LPG 2m3

Early explosion

3

1

2

4

Late explosion

3

1

2

4

Flash fire

1

2

3

4

Fireball

3

1

2

4

Average

2.5

1.25

2.25

4

Note: 1=highest. 2=high. 3=moderate. 4=low

Note: 1=highest. 2=high. 3=moderate. 4=low

Figure 5.16 Intensity radii for LH2 and various capacity of LPG

The results show that hydrogen poses less risk than LPG. The large effect distances for hydrogen especially flash fire (Fig. 5.17) are caused by the large energy density of the released gas and wider ranges of the flammability limit. A simple qualitative assessment (in Table 5-38) also shows that hydrogen poses lower consequences than of LPG. In this table, accident outcomes resulted from catastrophic rupture of the hydrogen tank (12 m3) and LPG tank (20 m3) were compared qualitatively.

Biogas Lpg
Figure 5.17 Flash fire impacts of LH2 and various capacity of LPG 5.6.3.4 The Risk Comparisons

5.6.3.4.1 Individual Risk

Individual risk of the two hydrogen study objects (i.e. LH2 at depot and filling station) were compared with the one of the LPG study. Figure 5.18 shows that the total individual risk of hydrogen storage objects are higher than that of LPG, but the maximum effect distances of the hydrogen objects are lower than that of LPG. For example, failure of hydrogen objects lead to fatal consequences from a distance of less than 350 m, while for the LPG is about 1200 m from the storage. Safety distances to an individual risk level of 1 x 10-6/yr of the hydrogen storages are about 330 m and 450 m (for LH2 at filling station and depot, respectively). Meanwhile, for the LPG objects are about 580 m and 1600 m (for LPG filling station and depot). This is due to the fact that hydrogen poses lower consequences than that of LPG (see previous section).

Figure 5.18 Individual risk comparison between hydrogen and LPG storages
Figure 5.19 Individual risk comparisons between of hydrogen and LPG transports

Figure 5.19 shows that the individual risk of the hydrogen transports at short distance is comparable to that for LPG, but their effect distances are smaller. Especially, the hydrogen pipeline shows the lowest effect distance of the all means of transportations. Failure of hydrogen transports lead to fatal consequences from a distance of less than 50 m up to 344 m (for GH2 pipeline and LH2 truck, respectively), while for the LPG is about 170 m up to 720 m (for LPG pipeline and truck, respectively). Safety distances to an individual risk level of 1 x 10-6/yr of the hydrogen transports are about 40 m up to 250 m (for GH2 pipeline and LH2 truck, respectively). Meanwhile, for the LPG objects are about 170 m up to 560 m (for LPG pipeline and truck). Based on the fact above it can be concluded that the hydrogen study objects have a lower individual risk than those of the LPG.

5.6.3.4.1 Societal Risk

Societal risks of the hydrogen study objects were also compared with the LPG objects. Fig. 5.20 shows the societal risk (F-N curves) for the hydrogen and LPG storages. The individual risks of the hydrogen storages are a bit higher than that of LPG, but their maximum fatality number is smaller. For example, failure of the LH2 station lead to maximum fatality number of about 230 people, while for the LPG station is more than 1000 people. The societal risks (F-N curves) of the hydrogen storages are comparable to those of LPG. The curves for both storages fall well in the acceptable of the UK ALARP zone (dotted lines), and fall above the acceptable risk criteria of the Dutch ALARA zone (solid lines). According to the UK ALARP, it means that the storages may be accepted for the public. Should the plants be implemented for the public, the risk must be reduced as far as reasonable and practicable, typically subject to cost benefit analysis. For the Dutch ALARA, however, the measures to reduce the risk must be implemented.

Figure 5.20 F-N curves comparison of the hydrogen and LPG storages

10 10' 10' 10" 10' FatalitiesfN or More)

Figure 5.20 F-N curves comparison of the hydrogen and LPG storages

10 10' 10' 10" 10' FatalitiesfN or More)

Biogas Risker
Figure 5.21 F-N curves comparison of the hydrogen and LPG transports

Fig. 5.21 shows that the societal risks as well as the maximum fatality number of the hydrogen transports are lower than that of the LPG. For example, the maximum fatality number for LH2 truck is about 30 people, while for LPG truck is more than 500 people. The figure also shows that the hydrogen pipeline showed the lowest risk compared with the LPG. In fact, the F-N curve obtained for hydrogen transports (GH2 pipeline and LH2 truck) are still below those of LPG transports. Both the hydrogen and LPG transports, however, fall within the Dutch ALARA (solid lines), and in the acceptable zone of the UK ALARP (dot lines).

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