ABSTRACT
Auditory alarms take many forms. Despite more advanced ergonomic warnings (Patterson, 1982) many warnings consist of horns, klaxons, whistles, sirens, bells, buzzers, chimes, and gongs. There are various characteristics and features associated with the different technologies of auditory alarms, such as intensity, frequency, conspicuity and noise penetration ability. Although much research has already been conducted in this area and improvements suggested and made as a result (e.g. Lower et al, 1986), this does not mean that all the problems have been solved, or that the information which already exists has filtered its way into current design practice. Case studies in coronary care (Stanton, 1993), intensive care (Meredith & Edworthy, in press), aviation (Thorning & Ablett, 1985), manufacturing and power generation (Stanton, 1992) show that although auditory signals may be successful in attracting attention, they can at times be disruptive distractions carrying little useful information about the problems of which they are informing. Further, a study by Patterson (1982) suggests that between 4 and 7 warnings
can be acquired reasonably quickly, thereafter performance slows down dramatically. Up to 7 warnings can be retained, even after one week of absence, and this figure could be up to nine if the warnings were presented regularly. It has been shown recently (Meredith & Edworthy, in press) that a greater number of warnings can be retained over quite lengthy periods of time. However, it is not just the sheer number of alarms which cause problems for the user; in many cases the alarm sounds themselves are confusing because theta are similar to one another either in sound quality or in meaning. There are also some problems in extrapolating from laboratory and in-situ testing to the way in which alarms are most likely to be heard in the actual work environment. For example, Weirs & Kershner (1984) suggest that although twelve auditory alarms may be discernible on a relative basis (in tests at nuclear power plants), if absolute identification is required this number is likely to be halved. There are at least two fundamental design problems. The first is how to design auditory alarms so that their meanings are conveyed to the listener in the most effective way. The second is the question of how many auditory alarms can be learnt and recalled comfortably. The two problems are interrelated, and one way to tackle them is to capitalise upon what the users understand about sound (including alarms and warnings) and its meaning.
