Article highlights confusion about Homeland Security safety symbols

January 28, 2005

SANTA MONICA, CA-- Safety symbols designed to instruct American citizens how to react if terrorists strike may confuse them, according to an article in the latest issue of Ergonomics in Design. For example, the symbol meaning "Use a whistle if one is available. Shout only as a last resort" was interpreted to mean "Yell when you hear a whistle."

In 2002, the Department of Homeland Security (DHS) introduced a series of pictorial safety symbols designed to help prepare citizens in the wake of specific scenarios that might occur during a nuclear, chemical, or biological terrorist attack. However, in a study conducted by Christopher Mayhorn, Michael Wogalter, and Jennifer Bell of North Carolina State University, participants were unable to comprehend the meaning of many DHS safety symbols.

Based on published safety standards, the authors concluded that up to 79% of the DHS safety symbols are "unacceptable for communicating hazard-related information." The study, described in "Homeland Security Safety Symbols: Are We Ready?" (Ergonomics in Design, Volume 12, Number 4, Fall 2004), details the limitations of DHS safety symbols and advocates for the inclusion of human factors methods in designing more effective safety symbols and systems.

Human factors, often referred to as ergonomics, is the science that explores human capabilities and behavior and how these characteristics are incorporated into the design, evaluation, operation, and maintenace of products and systems that are intended for safe, effective, and satisfying use by people.

The researchers found that much of the message content communicated by the DHS symbols is questionable or counterintuitive. The intended action or warning that some symbols are supposed to convey is so complex that it can't be adequately captured in a simple picture. Other symbols attempt to convey abstract ideas, which many study participants failed to comprehend.

In addition to the DHS symbols, the authors examined the Homeland Security Advisory System (HSAS), which communicates warnings of terrorist attacks using colors, words, and phrases in five different threat levels. Participants in another study conducted at North Carolina State University reported significant confusion in correctly ordering the colors and words attributed to the different threat levels of the HSAS system. Based on previous human factors research, much of the confusion about the symbols was predictable and could have been avoided had human factors methods been used in the design of the symbols.

The authors recommend improving future homeland security symbols by using several human factors solutions:

  • Selection of concepts through testing. Preliminary testing of concepts can allow designers to identify and avoid symbols with abstract, nonconcrete concepts, leading to more immediate comprehension.

  • Iterative comprehension testing and rapid prototyping. Prototype symbols should be developed, tested, improved, and retested for comprehension with a large sample of people.

  • Training via an awareness campaign. Recognition and use of safety symbols can be greatly improved with the use of a public campaign to encourage awareness of the symbols.
    For more information, or to obtain a copy of the issue of Ergonomics in Design mentioned here, contact Lois Smith at HFES (, 310-394-1811).

    Ergonomics in Design serves the needs of practicing human factors engineers and ergonomists who are concerned with the usability of products, systems, and environments. It provides up-to-date demonstrations of the importance of ergonomics principles in design and implementation. Articles, case studies, anecdotes, debates, and commentary focus on the ways in which human factors principles are implemented in the design, development, prototyping, test and evaluation, training, and manufacturing processes of a product or system.

    The Human Factors and Ergonomics Society is a multidisciplinary professional association of more than 4400 persons in the United States and throughout the world. Its members include psychologists, engineeers, designers, and scientists, all of whom have a common interest in designing systems and equipment to be safe and effective for the people who operate and maintain them.

    Human Factors and Ergonomics Society

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