by Russ Derickson, Ph.D., P.E.

Russ Derickson, Ph.D., P.E. is the Director of Science and Engineering at the Resilient Design Institute. He affiliated with RDI in late-2021 following a varied 40-year career as a software developer (REM/Rate that pioneered home energy ratings), atmospheric scientist, wind engineer, fire scientist, and building commissioning expert. You can learn more about Russ on the RDI Core Team webpage. This is his inaugural blog on the RDI website.  -Alex Wilson

Introduction

A few months ago, I wrote a letter to the editor of the magazine Civil Engineering in response to an article in which interviews of various experts revealed confusion and contradiction about the meanings and practical implications of sustainability and resilience, presenting them as separate ideas, both vital, that somehow needed to be combined and implemented. Some experts stated that resilience was a subset of sustainability while others claimed the converse.

To me it is clear. I offered that resilience operates to ensure sustainability and that they are inherently intertwined. Sustainability is about enduring function and cannot be achieved without resilience. The opposite is not true. A component, measure, or system that is resilient may not be sustainable by virtue of cost, limitation of resources, or environmental impact.

But what is resilience? After writing my letter to the Civil Engineering editor, I set out on a quest to explore further what has been written in the past about resilience and what has emerged recently in this era of extreme climate-induced threats. Thus, I would like to elaborate on the themes of sustainability and resilience to augment what is posted currently on the Resilient Design Institute’s web site.

Impacts of climate change have led to an explosion of newly published information on resilience in 2021 and 2022. I delved into these sources as well as revisited the seminal work on resilience by Amory and Hunter Lovins in their 1982 book Brittle Power. In my efforts, I began to see resilience as analogous to the function of our immune system, a form of biomimicry. In this blog, I explore the analogy and develop a guiding, comprehensive framework for resilience in support of sustainability – enduring function.

The Essence of Sustainability: A Hierarchy of Lifespans

The Sustain Pedal

Imagine the sustain pedal on a piano that enables a note or cluster of notes to fill a performance hall for some lilting span of time. We want certain things to sustain for various reasons, not least for enjoyment and crucial purpose. We don’t live forever, but want to live in health and wellness for a season of time that allows us to make our mark with purpose and chosen path. We don’t want viral or bacterial diseases to sustain, but viruses and bacteria play fundamental roles in processes that sustain life, so we don’t seek to expunge them, only diseases, which can be quite resilient.

Hierarchy of Lifespans

Buildings have lifespans that can be extended through good design, refurbishment, or repurposing into new life cycles. Sometimes they need to be razed and replaced. The same applies to infrastructure. Cities should and do exist longer than people, buildings, and infrastructure, as do entire nations. But what should sustain longest is life, itself, and the Earthly substances that nourish life. Long live photosynthesis, our inheritance from the sun and the Earth’s flora that sustains life. So, the sustain pedal commands a hierarchy of timelines for the life of various animate and inanimate elements and objects on Earth in which resilience plays an essential role.

Analogy of Resilience as “Immune System”

Exploring the Analogy

We can formulate resilience in our lives, communities, and natural settings as analogous to the function of our immune system. Thus, we can view resilience in terms of a dynamic framework inspired by the functions of health and wellness in our bodies, hence learning from nature, or biomimicry.

Our vulnerabilities to the various kinds and scales of climate-induced threats that intrude into our lives can be mitigated or even prevented with a properly designed, tuned, and well maintained “immune system” that watches over us in our built environment and orchestrates our relationship to Earth and its resources. That is, resilience as “immune system” acts in service to our wellbeing and enduring function, the primary themes of sustainability in our infrastructure, economy, social structure, lifelines, culture, and surrounding natural environment.

Any analogy has its breaking points, yet still can serve us well in our thinking and modes of practice. The immune system is amazingly powerful and comprehensive: it absorbs shocks and wards off a range of diseases, engenders healing from sickness and wounds, and improves its arsenal of defenses from what it “learns” from destructive encounters.

The health professions speak in terms of two aspects of the human immune system: innate and acquired. Critically, and central to what constitutes resilience, acquired immunity is an adaptive process. We inherit the first and achieve the second through the immune system’s processes of learning from invasive intrusions or by our direct intervention with such measures as healthy diet, exercise, vaccinations, pharmaceutical drugs, and activities that refresh the mind, including escapes into nature.

It is important to emphasize that some assaults can fatally override the capabilities of the immune system, thus human intervention is essential in certain cases but is not always successful. The immune system’s ability to learn from and defend against intrusions and our interventions can only go so far, as the COVID pandemic has tragically shown. These limitations apply as well in defending our built environment, but new concepts and practicalities of resilience we are gaining from research and experience are reducing the limitations we face.  

Design and construction for resilience is like the immune system’s innate ability to ward off injuries and disease. When intrusions are able to breach the barriers of defense, resulting in disease, they are fought by coordinated forces within the body’s network of organs to achieve recovery. Episodes of defense and healing spur a learning process, such that a similar assault tends to meet with failure or impose limited impact in a repeat occurrence. The challenge to the immune system is that it has the task of a learning curve for every unique assault it encounters. Modern medicine and genetic research are making inroads in improving this case-by-case process.

With respect to the built environment, lessons learned from an assault cannot generally be applied until a span of time later, unlike the near immediacy of learning and counteraction by the immune system. But the acquired knowledge arms designers, architects, city planners, policy makers, engineers, social service providers, and other practitioners with inspiration for new designs and novel operational frameworks to ward off similar future assaults. The acquired “immunity” becomes innate through ongoing learning sequences. The goal with newly assimilated knowledge is to “bounce forward” toward better designs and implementations after damage or disaster. This is what resilient design is all about.

Living systems and self-healing materials under development are refining the picture of resilience as immune system, making it more like our human system. It is also important to note that predictive tools and measures, including use of artificial intelligence (AI) and machine learning, themselves a form of biomimicry (e.g., neural networks and genetic algorithms), are bolstering our ability to foresee faults and catastrophic events that can disrupt or destroy our infrastructural and social lifelines. Humans are unique in nature with their ability to predict and to create predictive tools that augment the mind.

We have indeed come a long way, but the glaring truth is that certain extreme events and their magnitudes cannot be predicted, which places a severe burden on our responsive skills. One advancing shift in thinking is from so-called “fail-safe” designs to “safe-to-fail” concepts and implementation in which failure is not catastrophic. Various sorts of safe-to-fail structures are evident in nature. Amory and Hunter Lovins make some compelling arguments about “fail-safe” designs in Brittle Power.

Their claim is that “fail-safe” designs will fail eventually, at least in some aspect, if not catastrophically, because of the myriad possibilities of extreme threats and associated vulnerabilities that can never be fully known. Individual unknown threats may have low probabilities of occurrence, but their sheer number make it probable that at least one will appear at some point. This provocative statement of fact is intended to stir awareness of a “safe-to-fail” approach to design, construction, and operation.  

System is the Key to Resilience

The immune system is comprised of several internal organs that work together to engender wellness and protect and sustain the functioning of the body. Main components include the white blood cells and antibodies, the lymphatic network, the spleen, the thymus gland, the bone marrow, and other organs as shown in the figure below. Inherent in the immune system’s structure, the various organs operate to amplify the effects of other organs or substitute for defense and healing when other organs are weak or non-functioning. However, nature is not perfect and failure of some organs is fatal.

In general, the components that make up any system interact, provide feedback, operate in realms of hierarchy, and collectively can produce surprising, unpredicted behaviors. The more complex a system, the more difficult it is to understand, predict, and control. Thus, simplicity and modularity are goals we should seek in our designs, constructions, and operations.

An essential point often lost is that, while examining individual system parts in isolation to assess their functioning is an important sequence, it is not sufficient. It is necessary to analyze a system as a functioning whole, such that vital behaviors that emerge from the complex interaction of its individual parts are on track. The proper sequence is unit testing, integration testing, system testing, and acceptance testing. Assuring resilience requires nothing less than this standard of rigor.  

Key Attributes of a Framework for Resilience-As-Immune-System

A framework for resilience as immune system should possess the key traits of the human immune system, thus inherit all of its comprehensiveness and system-based properties: 1) innate ability to absorb and ward off (i.e., mitigate) injurious assaults; 2) capacity for recovery if an assault breaches the barriers of defense; 3) and acquisition of new defensive capability (i.e., adaptation) through learning from episodes of ever-changing assaults that have burst through the defensive barriers. A key factor is the facility for adaptation: continuous acquisition of new knowledge and improved skills.

The following figure illustrates the structure and operational flow of a framework for resilience-as-immune-system. We can refer to it as simply the resilience framework, or framework. It is important to state that the framework endows the concept of resilience with a larger, more comprehensive scope than does most, if not all, discussions about its nature and definition. To wit, mitigation and adaptation are often omitted in descriptions of resilience, but are inherent to the immune system. The powerful role our immune system plays in human survival and flourishing serves to legitimize its analogous application in dealing with survival, hence sustainability, of our built environment. Let’s explore the framework.

Starting from the left in the figure, the “mind” of the framework contains the innate knowledge for resilience, the facility for prediction of various situations and events, and the acquired knowledge from experience with assaults that pierce the defensive barriers. Over time, acquired knowledge diffuses into the “mind” of the framework and becomes innate as the system matures. Living and self-healing materials hasten the maturity. The “mind” of the framework contains predictive facility, which is unique to the human species, and takes many forms and roles. The advent of AI and machine learning add to predictive skills to detect and foresee faults.

To the immediate right of the framework “mind” are the preventative measures and processes of resilience that defend against assaults to the built environment. To the right of the defensive barrier are the curative measures and processes of resilience that enable recovery, with the goal of bouncing forward, not just back. The various preventative and curative measures and processes can be thought of as counterparts to the organs and networks in our immune system. During recovery, data is gathered for acquisition of new knowledge for dealing preventatively with assaults. The acquired knowledge also guides design of improved recovery responses to breaching assaults.

In the figure above, the reader will note the line of demarcation—the defensive barrier—that separates prevention from cure: defense from recovery. The common thought in medicine is that prevention should minimize the need for cure. That is substantially correct, but safe-to-fail design concepts in the built environment bring a certain intrigue to the discussion. Safe-to-fail designs take various forms. If a device such as a furnace fails during a winter power outage, safe-to-fail implies backup equipment or passive survivability measures to prevent death by freezing. In other cases, safe-to-fail means that a failed device is not crucial to system function or human survival, such that recovery is not pressing, or failed components can be substituted by other system components that are functional.

In yet other cases, certain items can be designed for less resilience because they are inexpensive and quick and easy to replace and their failure may not disrupt the system they serve for significant periods of time, if at all. There are also cases where threats that can occur are so severe that it is not economically possible to resist beyond a certain level of safety. Designing a home to survive an EF5 tornado probably doesn’t make economic sense, but creating a safe room within that house probably does.

Scenario planning must address such possibilities. There are also cascading system failures that propagate from component to component. Designs for such failures fall into the category of preventative measures and need to be structured to minimize, if not preclude, vulnerable component linkages that can lead to cascading effects.

A vital aspect of prevention vs. cure is that an unbalanced emphasis can set policy on a biased, short-sighted path. The Rand Corporation cites examples in which policy emphasis on post-disaster recovery measures can dangerously omit critical mitigation measures for societal safety. The human immune system does justice to both prevention and cure, and a framework of resilience-as-immune-system should do the same. However, a case-by-case total cost analysis is in order to sort out what is at stake and what are the relative benefits and costs for effectively balancing prevention and recovery.

Developing and Applying the Resilience-As-Immune-System Framework

The basic framework operates on a range of spatial and temporal scales. Critically, the built and natural environments will be treated in contrasting ways. The built environment and its immediately surrounding natural elements, including the wildland-urban interface, will be managed with more direct intervention than will wilderness. Evolution has placed us in a unique position of stewardship of the Earth. Sometimes that means benign neglect of certain elements in the wild and the “natural” on all scales. E.O. Wilson’s book, Half Earth (2016), features that perspective.

Other times and circumstances require more of our active intervention in the wild. The Wooing of Earth (1980) by Rene Dubos speaks of a symbiosis of humankind and Earth in a process of mutually adaptive responses and changes that is ever evolving in interaction between humans and nature. These points constitute a big set of topics and concepts beyond the scope of this current blog, but will be addressed to a greater extent in future blogs. The books Half Earth and The Wooing of Earth contain lots of insights and guiding wisdom that deserve far greater consideration.

In the built environment, the resilience framework can operate on the scale of a single building or an entire community, city, or state. It can be employed globally. In its usage, the framework needs to consider and attend to all critical linkages and dynamic interactions in the systems it addresses. Thus, not only the relevant components in a building need to be considered, but connections to lifelines that serve a building need to be included. In other words, systems contain other systems and subsystems that are crucial and interdependent in vital ways as a whole. For example, not only should all the features and components essential to functionality in a hospital be operating well, but also the modes and paths of transportations for patients and staff be operable to at least a threshold level in a disaster.

The resilience framework presented in this blog is conceptualized as an inclusive model to address all scales of the built environment and its interaction with the surrounding natural environment. The framework is structured by analogy for inclusion of measures that mimic how the immune system addresses morbidity, comorbidity, cascading assaults and propagating component failures, trade-offs, modes of recovery, and a host of other factors.

Vitally, the framework includes the distinguishing feature of the ability for prediction through the power of the human mind and its augmentation by AI, itself a form of biomimicry. The framework allows incorporation of critical application specific resiliency measures and processes for properly balancing both prevention and recovery, with an emphasis on a preventative approach to resilience that is in line with a vision for a flourishing, sustainable world.

Editor’s note: If you have thoughts on this concept, please add them in the comments field. -Alex Wilson