Cascading infrastructure failures and you!

Curtis Edwards, P.E., F.ASCE, Vice-President and Senior Project Manager, Psomas, San Diego, California; Laurence W. Zensinger, Vice-President, Homeland Security, Dewberry, Fairfax, Virginia; members of the APWA Emergency Management Committee

Cascading failure—when disruption in one infrastructure causes a disruption or failure in a second infrastructure.

When the public hears about cascading infrastructure failures, it is likely they remember the electrical network failures in the northeast where one failure in the electrical system led to many other electrical failures. However, it is unlikely that they think about the other infrastructure failures that resulted from this type of event. Power was out to traffic signals and electric trains, crippling the transportation system. Communications were also disrupted with the loss of power. It is easy to see how one small infrastructure failure can cascade into larger, multi-jurisdictional infrastructure failures.

Electric utility outage caused by severe storms and tornados in Georgia, March 2007 (photo by Mark Wolfe/FEMA)

All critical infrastructure facilities are almost always dependent on other infrastructure systems. This complicates the planning and mitigation of impacts related to the original failures. Preparing for these types of events is further complicated by the fact that these failures can impact multiple political, corporate and lifeline jurisdictions. Lessons learned from past events and dire warnings of future cascading failures often do little to improve emergency planners' and managers' capabilities.

A recent example of a cascading failure occurred during the Southern California wildfires when fires burned power lines, cutting off power to a critical water pump station. As a result, an entire community was without water while being surrounded by fire. The impacts continued into the next week as water service was restored but undrinkable due to contamination of the empty system. Similar disruptions could impact water-dependent facilities such as hospitals, which are even more critical systems during disasters.

I-35 bridge failure, Minneapolis, MN, August 5, 2007 (photo by Todd Swain/FEMA)

These critical infrastructures and others such as power transmission networks and communication systems are complex in their own right. However, in reality, these individual systems interact with each other in many ways, increasing the complexity of the failure. This makes the analysis and the subsequent mitigation even more complex. Some of these systems are coupled in such a way that the control of each one depends on the state of the other.

The complex agenda for hardening the nation's infrastructure in the aftermath of 9/11 and now Hurricane Katrina is still in its early stages. Other homeland security goals—such as strengthening the ability to respond to an attack or a catastrophic natural disaster and recover quickly—have commanded greater attention and resources, especially in the aftermath of Hurricane Katrina. In addition, as difficult as it is to develop a comprehensive capability to respond to and recover from natural disasters and terrorist attacks, protecting the nation's infrastructure from the loss of key assets that could result in cascading failures is even more difficult.

The National Strategy for the Physical Protection of Critical Infrastructures and Key Assets recently released by the Department of Homeland Security (see states that the primary functions of the policy include protecting national security missions, public health and safety. Additionally, the National Strategy recommends reinforcing state and local governments' capacities to deliver essential public services, protect the private sector, and to improve public confidence and morale.

What does this mean to local public works officials? There are a number of steps that can be taken.

First, understand the nature of infrastructure that traverses or serves your community. Which facilities would create the gravest economic or social impacts if attacked or knocked out by disaster? From this perspective, not all facilities may need the same level of attention or protection.

Second, try to understand the interdependencies among infrastructure systems. For instance, electrical outages can interrupt water supplies and cellular communications when power backups fall short. What opportunities are there to build in redundancy which would reduce restoration and recovery time?

Finally, look at some of the things that can be done to mitigate the effects of natural disasters or terrorist attacks on infrastructure. Mitigation measures for hazards such as floods or earthquakes are generally well understood and in use where necessary. For certain facilities that could be targets of terrorist attacks, consideration should be given to site layout and design (stand-off distance or barriers), structural design that will avoid collapse from the effects of a bomb if possible, and any special rescue and recovery plans or capabilities required if a specific infrastructure node in your community fails.

The great diversity and redundancy of our infrastructure provides for significant physical and economic resilience in the face of terrorist attacks, natural disasters or other emergencies. However, this vast and diverse aggregation of highly interconnected assets, systems, and networks may also present an attractive array of targets to terrorists and magnify greatly the potential for cascading failure in the wake of catastrophic natural or man-made disasters. Understanding critical infrastructure relationships and protecting critical facilities from all kinds of disasters is a significant challenge, but one which we should all be thinking about.

Curt Edwards can be reached at (858) 576.9200 or; Larry Zensinger can be reached at (703) 849-0139 or Both authors are members of the APWA Emergency Management Technical Committee.

Note: If you would like more information on cascading infrastructure failure, plan to attend the workshop session scheduled to take place during the 2008 Congress in New Orleans, Louisiana.