Uses of Risk Analysis to Achieve Balanced Safety in Building Design and Operations (1991)

In common parlance, risk is the possibility of loss or injury, a probability that some event will occur with serious consequence. Risk is inherent in all human activities, an unavoidable aspect of life, and a concern in all aspects of buildings and other constructed facilities.⁸ Fires, extreme weather, and earthquakes, are among the more obvious sources of risk that occupants and owners encounter in and around buildings, and are examples of the large variety of threats to people's safety and investment in property. Building professionals and government authorities have developed extensive design rules and building regulations in an effort to maintain risk at what seems to be reasonable levels.

Risk stems from many sources, and the levels of risk judged to be reasonable may differ from one community to another and from time to time. At a national level, an extensive and aging inventory of existing facilities is a source of concern that risk may be growing. Historic preservation of old structures, in particular, may pose problems when extensive physical changes

and adaptive reuse⁹ expose occupants and owners to hidden or unexpected problems. Through aging, any facility may experience progressive growth of risk, due to deterioration of building materials or other natural physical forces. However, the committee judges that as many as 90 percent of structural failures, regardless of structural age, may be attributable to human error at some stage of the facility development and use rather than to catastrophic natural events.

Risk¹⁰ arises because of a specific hazard—an act, event, or phenomenon—posing potential harm to people or activities or things. Fire, earthquake, wind storms, flooding, toxic and allergenic materials, and terrorist attack are examples of hazards associated with buildings and other facilities. The consequences of a hazard are the elements of harm that might result, including numbers of people exposed and severity of harm—e.g., deaths, injuries, dollar value of property damage, activities disrupted, area affected, legal liabilities, and environmental damage.

The idea of risk includes the magnitude of potential consequences of the hazard and the chances that the harm will be realized, that is, the probability of occurrence of the actual event or act, and subsequent loss or injury. Fire risk in a building, for example, may include fires starting from a number of possible sources and various outcomes depending on detection, alarms and fire fighting response when a fire is detected, weather, and the materials of internal furnishings. Each outcome has an estimated probability of occurrence. ¹¹

Safety is improved when risk is reduced. Risk is reduced by avoiding the hazard (e.g., avoiding flooding by not building in a flood-prone area), by reducing the chances of loss (e.g., using shatter-proof glazing in windows), or by limiting the likely magnitude of loss (e.g., using smoke detectors to give people more time to escape a fire). However, hazards and facility response to hazards are uncertain, and the assessed risk in any situation reflects the range of uncertainties as well as the levels of hazard and resistance to damage or loss.

Because there is always some risk, safety is not an absolute condition; it can be discussed reasonably only in relative terms. "Unsafe buildings" are those found to be in a condition that is demonstrably dangerous or a hazard to life, health, property, or safety of the public or occupants (BOCA, 1985), according to defined standards of measurement or the judgment of appropriate authorities. Safer facilities expose their owners, occupants, and neighbors to less risk, i.e., fewer or smaller hazards or lower probabilities of occurrence or some combination of these factors.

Building risk and safety depend on where facilities are located, when and how these facilities were constructed, the activities they house, and how they have been operated and maintained. [See box next page.] Some facilities—for example, research hospitals and military installations—may expose their occupants to unusual risks such as infectious diseases or ammunition explosions. Other facilities such as nuclear power installations or toxic waste depots may present unusual risks for people and activities in the vicinity of the facility and over large areas. Risks for handicapped people, children, or people with particular medical conditions may be greater than for other groups.

Risk in and around buildings stems from a wide variety of specific hazards. (See Table 1) From time to time, new hazards are identified and become the subject of debate, public policy and regulation. Radon gas, for example, has been recognized as a potential hazard only within the past two decades, while the toxicity of lead has long been known.¹² The hazards and risks of electromagnetic radiation from such sources as video display terminals, microwave ovens, building wiring, and electrical transmission and distribution lines are still being defined. New technology, design details, or construction practices may give rise to new or greater risks.

Various mechanisms are used in design, construction, operations, and maintenance to limit risks in and around buildings, including government regulations, construction and building inspection, and operations by fire departments. Local and state government building codes¹³ and design

criteria used by professionals are the most common and comprehensive of these mechanisms. Federal government agencies, although not strictly subject to local building codes, have adopted similar requirements to protect the health and safety of their own workers as well as the public at large. These criteria and codes generally seek to restrict or eliminate specific hazards, and do not typically recognize the principle that risks cannot be completely avoided. Some codes and criteria do reflect at least an implicit recognition of probabilities of occurrence.¹⁴

Building codes typically address only about 20 percent of the concerns that an owner's design criteria will encompass (Building Research Board, 1989). Some risks not addressed in codes may be limited through application of

standard professional practice or explicit decisions by facility owners, and others—such as health-threatening air pollution and flooding along shorelines—are the subject of national regulation.¹⁵ Some risks—such as electromagnetic radiation—have not yet been debated or determined to warrant regulation.

Generally speaking, facility risks in areas subject to particular hazards (such as earthquake, flooding, or criminal activity) will be higher unless specific actions are taken to control the risk. Some risks increase with age of the facility because of normal aging and wear of materials and equipment, unless maintenance efforts, sound management practices, and appropriately timed rehabilitation efforts slow or reverse such normal deterioration. Facility designers and owners sometimes act to limit risk by installing detection devices (e.g., smoke and ionization sensors, water detectors for flooding, pressure sensors, security devices) to give early warning of increased hazard or probability of loss.

Uncertainties in projecting uses, loads, environmental conditions, and performance of equipment in service are among the factors making it difficult to limit risk using codes and design criteria. Such mechanisms may also be inadequate when new hazards arise. Systems for identifying potential problems as they develop and responding on a case-by-case basis may then be warranted. Fire departments and disaster relief programs are principal examples of this mechanism for limiting risk. Monitoring of building loads and structural deflections and regular inspections of key subsystems (e.g., for corrosion and wear) serve also to manage risk. Inspection, testing, and other quality control activities in design, construction, and operation are undertaken to avoid increasing risk due to errors or oversights of the designer, faulty construction practices, or inadequate operation and maintenance programs. Risk management professionals seek to assure that risks that cannot be physically limited are effectively reduced or transferred through such means as insurance, emergency response planning, and damage control.

Mechanisms for limiting risk have a cost, and a balance must be struck between levels of risk and the costs incurred by facility owners, users, or the

public¹⁶ to reduce risks. While current design practice, building codes and inspection procedures are intended to assure levels of safety that the public finds acceptable, there is no mechanism for comparing risks from diverse sources. Current practice places emphasis on some sources of risk while seeming to neglect others. [See box next page.] The committee concluded that overall safety can be improved through more effective allocations of resources to manage risk, and that risk analysis is a useful tool for helping those who must make these allocations.

Risk and safety levels currently are seldom measured in explicit terms. The levels of risk and safety that the people find acceptable evolve through a process of professional consensus and public debate.

Professional consensus is developed in the forums of professional societies and model codes organizations.¹⁷ The process may be informed by extensive testing and measurements in laboratories and field situations, and by the experience of professionals working in the field. Such organizations as the Underwriters Laboratory, Factory Mutual Research Corporation, and the National Institute of Standards and Technology, as well as many other federal government agencies and university and corporate facilities, play a key role in accumulating the information upon which consensus is based.

For some hazards, the consensus is expressed as measures of performance that a building should exhibit, and the building professional is left to make informed decisions about how to achieve that performance. For example, many structural configurations are permitted for a building, so long as forces anticipated in the structural members (computed according to accepted methods) do not exceed the strength of the materials (as determined by accepted tests). For other hazards, such as fire, building professionals are presumed to require more specific guidance, expressed as explicitly required design features or management procedures. For example, sprinklers may be required in newly constructed hotel rooms, regardless of the facility's materials and design. However, in either case, the level of risk is judged implicitly to be acceptable if the requirements are met.

Public debate comes into play when professional consensus cannot assure that safety is adequate or seems to have missed the mark. A particular disaster such as a multi-fatality fire or loss of life in an earthquake may motivate the debate. At other times, debate may spring from discovery of a new hazard, such as threats to health posed by asbestos. In either case, demands are made for action aimed to increase safety, and new regulatory practices are typically the means adopted to assure the increase.

A number of studies have attempted to assess risks faced by individuals and groups in modern society, and to compare the risks associated with various hazards. However, there are no commonly applied comprehensive measures of safety or standards of acceptable safety.

Furthermore, people seem to demand much lower levels of risk when they are dealing with particularly feared or unknown consequences. (See Figure 1

Figure 1. Comparisons of perceived risks from a variety of sources (Source: Slovic, et al., 1985).

for example.) People seem also to accept higher risks when they can choose voluntarily to do so, as compared to situations in which they are exposed involuntarily to risk.¹⁸ (Fischoff, 1984; Kraus and Slovic, 1988) As a result, the levels of risk in and around buildings may differ substantially with respect to various hazards, and may be higher than those associated with hazards from other sources that attract current public concern.

Many risks are treated according to the public attention they attract. Occurrence of a fire that causes loss of several lives in a community will almost invariably lead to reexamination and revision of the fire safety portions of that community's building code. In such a case, the issues of fire safety may overwhelm efforts to manage risk from other sources.

Risk analysis may be used to assure a better balance of effort to achieve safety. Whatever amount is spent to reduce risk in and around buildings, safety will be at its maximum achievable level when these resources are allocated to achieve balanced reduction of risk from all manageable sources, rather than by concentrating on one risk.

Allocation of substantial resources to control risk from one source while other sources are relatively neglected is inefficient and produces safety below optimum levels. Wider application of the logic and procedures of risk analysis can benefit facility design and management. Risk analysis, as an instrument of risk management, can encourage forethought and better informed decisions.¹⁹ Experience in other fields confirms that formal risk assessment contributes to improved overall safety and a better balance of effort to reduce risks.

The principles and practices of risk assessment apply equally well to protection and safety of property as well as people. Probabilistic methods to compute expected net costs or benefits of various courses of action are frequently used by private sector and government decision makers seeking to manage their levels of financial risk. However, the protection of life safety is a primary concern of building professionals and the public, and cannot be addressed in financial terms alone.