Risk and resilience analyses

In the course of growing threats through terrorist attacks in Europe and Germany, the topic of constructional civil protection against terrorism is becoming ever more crucial. On the one hand, there is more need to quantify the potential hazards and risks posed by terrorist threats, and on the other hand, the constructional civil protection, especially of critical infrastructure, has to be implemented preemptively.

Against this background, Fraunhofer EMI has been commissioned by the Federal Office of Civil Protection and Disaster Assistance (BBK) to conduct a research project on risk analysis in terms of urban development. The research objective was to develop the computer program Explosion Effects in Cities (ExE-Cities) which gives answers to the following questions: 

• What kind of infrastructure is under threat?
• What consequences have to be expected?
• How can protection be accomplished?

The answer to the first question is given in the course of the scenario analysis. As part of the scenario analysis, the infrastructure that has to be protected and assessed is defined and a threat analysis is conducted by means of a database-assisted assessment procedure. These data are based on the evaluation of a worldwide database maintained by Fraunhofer EMI on terroristic attacks. As a result, critical infrastructure is identified. Figure 1 shows a color-coded example of the threat analysis. In this scenario, the townhall, banks and the train station are marked by yellow-orange coloring to indicate especially threatened infrastructure. In the end of the scenario analysis, the program user defines a specific scenario based on the results of the threat analysis, as, for example, the attack on the train station with a 1000-kilogram load.

In the hazard analysis, the physical quantities that describe the effects of an explosion event are ascertained for all locations of a specific scenario. The analysis considers both ideal and complex blast-wave propagation. The problem of complex blast-wave propagation in urban areas, as exemplary depicted for crossroads in the figure below, have been investigated within the scope of an extensive testing program. The experimentally determined pressure-time curves form the basis for the quantification of building damages in the subsequent damage analysis.

The question “What consequences have to be expected?” is answered within scope of the damage analysis for persons and buildings. This ascertainment can be related to the level of the overall load-bearing structure as well as to the level of building components. The figure below shows the result of a damage analysis for a scenario with a 1000-kilogram load. The red-colored circle with a radius of 86 meters denotes the area where the failure of a wall of 24 centimeters thickness is expected in case of ideal blast loading, therefore considering simple perpendicular reflection. The expected failure distance in case of complex blast-wave propagation extends to 117 meters. This example demonstrates that an approach that takes into account complex blast-wave propagation is required for the exact assessment of building damages in urban areas.

Concerning the expected damage to persons, the danger of collapse of the building as well as the danger due to blast are illustrated. This way, the software helps to determine the expected consequences for persons within buildings and persons close to buildings. After damage analysis, the implemented catalog of protective measures presents to the user the possibilities how to minimize the expected consequences of an event. Apart from organizational and structural protective measures, distance has proved to be one of the most effective solutions.

Precise risk analyses in urban areas allow to define endangered areas and building configurations in advance by evaluating the consequences of specific events. Thereby, the effort for adequate security measures can be purposefully minimized (see Figure 3 and 4). In addition, subsequently to the results critical buildings can be evaluated and reinforced with specific focus on their robustness.