Cost of Red Pumps

NEWSLETTER ARTICLE

A key criterion for an effective color code is that it is unique – the stimulus (color) means one and only one thing. Another criterion is that color codes should match population stereotypes or expectations where possible; for example, use yellow for caution. The two criteria come into conflict with the use of the color red, which has popular stereotypes for both stop and warning/danger. Many display standards achieve the uniqueness criterion simply by choosing that red will mean either stop or warning and selecting a different color to indicate the other. However, many companies, and even the American Petroleum Institute, use red for both warning (alarms) and stopped/closed. What does this violation of the uniqueness criterion cost in terms of human performance?

Figure 1. Display Used in Experiment

Students at Wright State University addressed this question in their senior design project in human factors engineering. They tested multiple targets (alarms) with different time constraints using one basic display where red meant only stopped pumps and another version where red indicated both stopped pumps and alarms (Figure 1). In this project, students measured three performance variables: number of missed alarms, number of false alarms, and time to fixate on the alarms. The latter was the determined by using eye-tracking software to determine exactly where the subject was looking. In addition, the interaction between accuracy and the time constraints was examined to determine if a speed/accuracy effect was present. The results of all of these were statistically significant at the p=0.05 level (less than a five percent probability that the results were due to random fluctuations).

Display designers often think they are doing the right thing in having red mean both stopped and warning. It satisfies the population stereotype criterion. However, it comes at a cost. The costs are:

1. being 10% less accurate,
2. having three times as many false positives,
3. taking 20% longer to find the alarm, and
4. making more errors as the time demands increase.

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