Blackout

Classification of blackout situations should ideally be based on all the important factors that influ-ence the severity of an event. Consequinflu-ences of an event can e.g. be measured in terms of:

• Magnitude of the disturbance in terms of power interrupted (MW).

• Duration of the outage (Hour). Duration of a power outage due to a system collapse will of course vary as power supply is restored at different times in different areas. In this analysis we have defined duration to be the average duration obtained by dividing the total energy not supplied (MWh) with the interrupted power (MW).

• Other circumstances.

Magnitude and duration of a blackout are the consequences that are directly measurable and most easily predictable. Other circumstances include all other factors that contribute to the severity of a blackout, for example the number of people affected, injuries or loss of life, weather conditions and time of year, extreme damages to equipment and installations. Many of these factors can be regarded as functions of the magnitude and duration of the blackout, and thus the impact of these factors are to some extent included. However, some consequences that are obviously very impor-tant when assessing blackouts, may be difficult to quantify or estimate in advance. This is the case e.g. for the most critical consequences like loss of life. Such extreme consequences must of course be taken into account, but in our analyses they will only be considered when distinguishing be-tween critical and catastrophic events.

As a basis to judge the severity of a blackout with respect to its duration, the following table from [17] is used to illustrate some consequences. Although the report is from 1984, most of the effects are very similar today, but the role of telecommunications and computers has increased signifi-cantly. This has probably increased society’s sensitivity for a blackout. E.g. production in much of the service sector will stop completely as soon as computers become unavailable, but in a com-parison with 1984 we should not forget that many activities would stop anyway because of their dependency on electricity.

Table 3-5: Sensitivity for blackout of various functions (without priority). Source: [17]

Time Function Consequence

1 second Magnetic cranes Flight control Computers Process industry

Load can fall down Impact on air safety

Loss of information and work

Stop of processes with resulting several hours down time

10-15 minutes Smelters

Computers with battery backup only

Floating material under transport must be recov-ered

Systems stop, but no loss of information 15-30 minutes Poultry farms Animals may die

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Time Function Consequence

TR F5962

Elevators Underground

It becomes unpleasant to wait in a stuck elevator It becomes unpleasant to wait in a stuck train 30 minutes Process industry

Smelters

Stop of processes, down time of up to 24 hours Risk of hardening of ovens

2 hours Pig farms Dairies Water supply

Ventilation problems, possible deaths of animals Reduced production

Some areas start to loose water 6 hours Smelters

Greenhouses

Hardening of ovens, considerable economic losses Damage due to drying of freezing, depending on the time of year

8 hours Water supply Heating systems Dairies

Risk of penetration of polluted water due to loss of pressure

Some buildings may start to become unpleasantly cold, problems for nursing homes

Risk of illness and continued reduced production 10 hours Telecommunication Backup batteries emptied, traffic stops

12-24 hours People and animals Road transport Food

Buildings

Wastewater treatment

Access to water and food

Empty petrol tanks, filling stations not working Refrigerated and frozen food starts to get spoilt, problems with distribution to consumers

Many buildings become very cold, beginning dan-ger of frozen water pipes

Risk of collapse of the water treatment with result-ing long down times

Several days Everyday life Reserve power

Does not function. Many companies close. Severe problems with water supply, food and heating.

Lack of fuel, need for maintenance, increased probability of failure

Reference [18], which also refers to [17] and [23], points at the fact that the consequences of a blackout depend on a number of other factors like:

Geographical and demographical conditions. The consequences become more severe if a large geographical area and more people (with certain share of needing people) are affected.

Climatic conditions. The consequences for households and in effect all buildings are more severe during especially cold weather. In warm periods there is a danger for spoiling of refrigerated and frozen food.

Preparedness at the individual level. Households may have alternative heating systems to some extent, though this only to a limited extent in towns. Other consumers can reduce damage if they have functioning backup generation for at least a part of their consumption.

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Collective preparedness and the availability of resources. Municipalities play an important role in the initial handling of a crisis through information and services to those who are affected. An im-portant issue is if municipalities have sufficient resources for this kind of crises.

Summing up, society appears to tackle blackouts of up to 12-24 hours without severe negative consequences, assuming that certain activities like hospitals and telecommunications have various forms of well-functioning reserve power. Long blackouts of several days severely disrupt society.

In order to carry out the risk analysis it is necessary to establish a quantitative description and classification of consequences. The quantification is done in terms of magnitude and duration of the blackout, and the chosen intervals and limits are based on the discussions above and the refer-ences provided. Table 3-6 summarizes the classification and intervals for blackout situations that will be used. The border between the different classes of events should not be interpreted as abso-lute, as they only cover the directly measurable consequences. Other circumstances must also be taken into account when possible, and especially if an event is close to the border between two classifications.

Table 3-6: Consequence classification and intervals for “Blackout”-situations Consequence

clas-sification Power interrupted (MW)

AND

Energy not supplied (MWh)

AND duration (hours)

Minor < 2000 <1000 < 2

Moderate < 4000 < 4000 < 8

Major < 8000 < 16000 < 18

Critical < 32000 < 64000 < 32

Catastrophic Otherwise (but strongly dependent on “other circumstances”)

The border between the different classes can be plotted in a magnitude-duration diagram as shown in Figure 3-11.

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Figure 3-11: Consequence classification and intervals for “Blackout”-situations Figure 3-11: Consequence classification and intervals for “Blackout”-situations