The Problem

From experience on a number of projects in safety critical industries, including rail and nuclear power, it has become apparent to Liv Systems that audible alarms in operational environments such as control rooms are often a contentious Human Factors issue. It is commonplace for there to be disagreement amongst the operators regarding which alarm tones would be appropriate for various alarm priority levels. Also, the range of alarm tones which are available for operators to select from often seem to be rather unsatisfactory, with none of the available tones being quite what the operators are looking for. Whilst as Human Factors consultants we can provide guidance on the selection of appropriate alarm tones, we find we are often constrained by the need to choose from a limited selection of less than ideal tones.

Current approaches to developing alarm tones tend to focus primarily on ensuring that the following standards are met:

• BS EN ISO 7731:2005 Ergonomics: Danger signals for public and work areas (auditory danger signals)
• ISO 11429:1996 Ergonomics: System of auditory and visual danger and information signals

Whilst it is important to design alarm tones that comply with these standards, focusing purely on standards compliance, in a kind of box ticking approach, does not ensure the development of alarm tones which represent a well designed acoustic experience for the end user. Put in simple terms, the resulting alarm tones can sound pretty ghastly!

The Creative Human Factors Engineering Solution

What is needed therefore is to apply a creative Human Factors design approach to the development of alarm tones, so that not only are the standards met, but also alarms tones are created in which the whole is greater than the sum of its parts. The development of good alarm tones should be approached not purely as a science but also as an art, incorporating creativity into the design process.

Therefore, Liv Systems have been working with the sound designer Gareth Worthy (see our previous blog post interview with Gareth) to develop a number of audible alarm tone ‘families’. Each family of alarm tones has alarms of various priority levels from ‘critical’ down to ‘low priority’ and follows a consistent sound type/category.

Audible Alarm Tone Families

We have developed 3 alarm tone families:

Pure Tones

These are simple square waves or saw waves without any of the more complex acoustic features that may be associated with musical instruments such as timbre.

Musical

Sounds based on musical instruments are far more acoustically complex than ‘pure tones’ since for any given note on a musical instrument, in addition to the fundamental frequency of the note itself, there are numerous other frequencies which are emitted which give the instrument its characteristic sound or ‘timbre’.  Using musical instruments as the basis for alarm tones has the advantage that due to their acoustic complexity, they are more likely to stand out from other sounds in the environment. Also, as there may be multiple systems in a control room environment, each with their own alarm tones, the use of musical instrument based alarm tones increases the chance that the alarms will be distinct from other alarms in the environment.

Futuristic

We had not originally planned to develop a set of ‘futuristic’ tones, but through serendipity, as a result of the creative design process, we found that some of the alarms we were developing had more of a ‘sci fi’ feeling, and furthermore these alarm tones seemed effective and appealing. As with the musical tones, these tones have more acoustic complexity than the pure tones. They are based on an electronic/synthesiser sound.

Next Steps

We are close to completing the design of our 3 families of alarm tones. We believe that by working with a sound designer, we have developed sets of alarm tones which will not only prove to be highly effective and have clear and consistent stratification according to alarm priority levels but will also be appealing to the end users thereby providing a significantly enhanced user experience.

Our alarm tones will be available in the near future for purchase as downloadable WAV files, based on a one-time fee (non-royalty) under a standard licence. We will provide further updates once they are available for purchase.