ISO/IEC 60601-1-8, Patterson and other alarms in medical equipment This page by Chris Thompson 27 July 2000 If this text is too small or too big, try changing the default font sixe in your browser's preferences. Clicking on the blue underlined link should play the sound. Most of the sounds are 8bit 22kHz mono uncompressed files in Windows 'wav' format, however the Patterson sounds are 16bit 44.1kHz files. File size varies between 30 and 250 kB. Time lags when playing sounds may be reduced by downloading the whole sound set as a web archive, then running the page as a local file on your computer. 1. 60601-1-8 type sounds 1.1 Urgency encoded
1.2 Combined category and urgency encoding (Apendix HHH; Block/Hakkila/Thompson)
2. Patterson Sounds The "Patterson" sounds on this site are a demonstration set designed in October 1985 by Roy Patterson and a team from the Applied Psychology Unit from Cambridge in conjunction with the Institute of Sound and Vibration research from Southampton. This group had designed alarm sounds for the British nuclear and military applications and were pre-eminent in this field at the time. Patterson's sounds were designed to illustrate the principles underlying sounds that could be used in a Draft International Starndard for Alarm Sounds that was being developed at the time by ISO TC1 SC3 WG1(aka Working Group 1 of Subcommittee 3 of Technical Committe Three of the International Standards Organisation). The samples here were digised from a stereo tape recording digitised and sent to me by Frank Block. The entire tape is available here in mono mp3 format (9.4Mb) and here as an uncompressed mono wav file (112Mb). Each individual sound is reproduced below in mono wav format. Patterson proposed two basic types of sounds, general and category-specific. Three forms of the General alarm sounds were provided, on the basis of urgency: Information Available, Caution, and Emergency. The Information available sound was intended to be played once only, whereas the Caution sound was to repeat every 30s and the Emergency sound to repeat every 15s until attended to. Category-specific sounds were constructed for oxygenation, ventilation, cardiovascular, artificial perfusion, drug administration and temperature. Each of these unique sounds was provided in Caution and Emergency forms, to be repeated at the same intervals as the general sound (30s and 15s respectively). The underlying principles included, as far as I can tell:
As indicated on the tape, "These are not the only sounds that satisfy the design principles, nor are they necessarily the best that can be constructed". As it turned out, the "Patterson" sounds on this tape were not endorsed by the group that considered them. Instead, in 1994 - nine years later! - they released "ISO 9703.2 - Anaesthesia and respiratory care alarm signals Part 2: Auditory alarm signals". The '9703' sound set was a simplified version of Patterson's 'general' sound. It did not make use of any of Patterson's psychoacoustic cues, the underlying sounds were based on simple beeps, there was no 'information' signal, and none of the category-specific sounds were included. 60601-1-8 attempted to improve on 9703.2 by bringing back an information signal, providing advice on how to implement psychoacoustic cues, and defining standard melodies for the 6 categories (plus one more for power-down). Frank Block, who sat on all the above committees, is of the opinion that the Patterson sounds were 'genius'. Here are the sounds: 2.1 "General" sounds - urgency encoding alone:
2.2 Category-Specific sounds (combined category and urgency encoding): Six categories were defined, each with their own specific sound pattern. Greater urgency is indicated by repeating the same melody twice - and making it louder, at higher pitch, in a faster tempo and with more rapid rise times- just as it is intuitively obvious that "FIRE!, FIRE!" is of greater ugency than 'fire' or 'hello'.
Distinctive as Patterson's sounds are, succesive IEC committees have not endorsed them. Mostly this was, I think, because simpler devices would have found it difficult, technically, to generate such complex sounds. Hence the simpler, more easily generated pulse tones of 9703.2 and 60601-1-8. None the less, the underlying psychoacoustic principles advocated by Patterson are, I think, entirely valid, as was the concept of providing unique sounds for the main categories of medical alarms. My greatest reservation with the existing 60601-1-8 melodies is that the high priority melodies are too complex. Although the high priority sounds are based on the medium priority melodies, two additional beeps after the base melody confuse the sound greatly, so that each high priority alarm is quite different from its medium priority version. This means that there are almost 13 different sounds to learn, and they can be too easily confused. The general rule of thumb is that people can learn 6-8 sounds of similar form. I very much prefer Patterson's category-specific sound concept, in which the same medium sound is just repeated twice, because once the melody for the medium alarm is known, the high form is basically just the same, and requires no additional learning. So my suggestion is to apply Patterson's concepts to a reduced set of melodies based on ISO 60601-1-8. I propose having only General (no melody), Cardiac, Oxygen, Ventilation, Drug/Fluid and Power-Down categories, with medium and high forms of each, plus the 60601-1-8 low priority or 'information available' tone. Time between annunciations and all other characteristics would be as per 60601-1-8. This approach reduces the number of melodies to learn to 7 (including general, advisory and power down sounds). This should avoid confusion and enhance ease of learning, though this is yet to be demonstrated in a clinical trial. In the table below I have included a 'very high priority' column to show how speed, rise time and volume can additionally emphasise urgency.
A significant advantage of this approach is that the high priority alarms are annunciated in much less time than the existing 60601-1-8 high priority sounds. For example, my 'very high' alarm sound takes only 1.3 seconds to fully annunciate, whereas an equivalent 60601-1-8 high alarm sound takes 4.6 seconds. In an emergency, when multiple alarms happen at once, brief alarms are less likely to overlap with others, whereas multiple long-duration 60601-1-8 high alarms will result in a cacophany - like 'everyone shouting at once'. A trial comparing these was done by myself and Penny Sanderson. As anticipated, the simpler sounds were easier to learn, and we also found that people with any musical training at all were better at identifying them than people with no musical experience at all. This work unfortunately went un-published.
4. The "new" Edworthy Alarm Sounds Judy Edworthy has written extensively on alarm sounds. The committee invited, and BSI supported, an effort by her team to produce a new set of sounds for a future edition of 60601-1-18. The Edwroty sounds consiste of a 'beeping' tone for urgency, which is optionally mixed with a sound indicating the kind of alarm. The following table includs draft sounds from 2019
Judy's initial studies suggest that these sounds aare easier to categorise than 'melodic' type sounds. I'm not sure of the status of this proposal. The standard allows any sound set that is not worse than the standard sounds. |
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