IEC 60601-1-8 Guidance for Designing Medical Equipment Alarms

There are many challenges to designing medical equipment above and beyond the design of consumer equipment. In addition to higher reliability standards, medical equipment has more stringent and specific requirements. This makes sense as the stakes are much higher than with consumer electronics, where equipment failure is literally a life-or-death difference.

One aspect of medical equipment that is often overlooked is the way the equipment communicates with its users. Visual indicators are incredibly useful, vital even, and can convey a significant amount of information in moments. However, they require the user to pay specific attention to the equipment. Audible signals, however, can catch the attention of people in and out of a room, leading them to come and review the situation and gain information.

However, one of the challenges is that if there is a large variety of different medical equipment, which is more than likely in hospital settings, there could be a cacophony of confusing and conflicting audible tones. Different frequencies, loudness, and patterns would require rote memorization of a large variety of signals, which would almost certainly add to confusion instead of clarifying. Thus, the IEC 60601-1-8 standard was created to provide guidelines to designers on how to create medical equipment that quickly and clearly communicates the intended message to doctors, nurses, and other attendants. This article will review this standard in more depth and help to decipher a few of the nuances involved.

What is the IEC 60601-1-8?

As we start getting into IEC 60601-1-8, we should note where this actually comes from and the authority by which it is created and implemented. This was created by the International Electrotechnical Commission (IEC), a European-based standards organization that created the IEC 60601 technical standard that addresses all medical equipment. IEC 60601-1-8 is a subset that specifically addresses medical alarm systems. The verbose title of this subsection is: General requirements, tests and guidance for alarm systems in medical electrical equipment and medical electrical systems.

Like nearly every technical standard, this is a long and detailed document that provides explicit instructions on nearly every conceivable alarm. It includes instructions on when alarms should be triggered, how their priority is classified, and perhaps most importantly, provides the different patterns that define exactly what the alarm will sound like. Signal burst pattern, pulse shape, pulse frequency, rise/fall time, and amplitude are all given. There are regulations given to separate alarms from technical issues where there are potential faults with the equipment itself versus problems with the patient. While these alarms are all well-regulated, it also explicitly allows for more sounds to be used, like music or voices.

Outside of the more general guidelines, the IEC 60601-1-8 standard also outlines important technical metrics pertaining to medical alarms, such as:

• The alarm frequency must be between 150 Hz to 1,000 Hz and must be one of four harmonics with the greatest sound level.
• There must be a minimum of four frequency peaks between 150 Hz and 4,000 Hz.
• The sound level of the greatest four frequency peaks between 150 Hz and 4,000 Hz must be within 15 dB of each other.

While this standard originated in the European Union, it is mandatory not only in the EU but also in the US and Canada. This is hugely beneficial for product designers to promote simpler compliance in multiple major locations and improves device safety and performance across the globe.

Medical alarm systems part selection

There are many components that can be used for the audio portions of a medical device. Sirens, buzzers, and even bells can be used, though other transducers are very common as well. These components are not equal and vary significantly in the difficulty of implementation, cost, power consumption, and flexibility. Electrical buzzers check the boxes in terms of cost, ease of implementation, flexibility, and power efficiency. Buzzers are unique because they either use electromechanical drivers, sometimes referred to as magnetic buzzers, or piezoelectric drivers, using a ceramic piezo driver. Because of these options, you can get different voltages, frequency ranges, sound pressure levels, footprints, and more, making buzzers the ideal choice for many alarms. In particular, Piezo buzzers are known for creating a louder signal (larger sound pressure level) than their electromechanical counterparts for the power consumed.

Figure 1: Same Sky buzzer designed for medical applications. (Image source: Same Sky)

With buzzers, you also have the possibility to customize their output so that a buzzer can, without any special driver, create the precise tone required by IEC 60601-1-8. Same Sky has created an array of medical buzzers that not only meet the audio requirements set out by the guidelines but also meet the robustness requirements outlined. The tones available are identified in IEC 60601-1-8 and correspond to the more common concerns found in the medical industry (click the links below to listen to the specific tones):

• Cardiovascular, which sounds somewhat like a heart beating.
• Oxygen, which sounds similar to a dripping noise.
• Ventilation, which sounds like someone breathing.
• General, which is a more generic sound.

Figure 2: Sample waveforms of specific medical device tones. (Image source: Same Sky)

Speakers versus buzzers in medical equipment

While IEC 60601-1-8 is focused on the sounds, the waveforms, and where the buzzers are used, it does not provide significant direction on what exactly should be used nor where it should be placed. While there are many benefits to buzzers, and they work in a wide range of applications, as mentioned earlier in this article, there are other options. While not as energy efficient as buzzers and more difficult to drive, speakers offer almost limitless flexibility in the sounds they make. Fully human voices, music, and any mixture of sounds, even at the same time, are all possible using a standard speaker.

There are directions in IEC 60601-1-8 about how speakers tend to make popping noises when there are sudden voltage changes, like when old headphones were plugged into a receiver or computer. While shaping the noise waveforms, you can avoid any sharp changes that would cause these noises, however, you will need to account for unexpected noise. Properly sized capacitors can absorb high frequency noises if they do not interfere with the intended signal. Physically protecting the connections from potentially coming into contact with outside electrical sources, including static electricity, will also help with this concern. Overall, while speakers are more of a challenge and require more thought in their implementation, they are an excellent choice when extra flexibility is needed. Same Sky has also developed specific medical speakers designed to meet the IEC 60601-1-8 guidelines.

Conclusion

Medical equipment is and will continue to be in great demand and expectations will also continue to rise. Fortunately, with clear and detailed instructions, the IEC 60601-1-8 standard codifies and simplifies the alarm aspect of medical equipment. While intense and potentially daunting, properly done, audible medical alarms can significantly increase the effectiveness of equipment and potentially save lives. To decrease the barrier to entry and any difficulty in implementing these guidelines, Same Sky has created medical buzzers and speakers that meet IEC 60601-1-8 requirements. For more explicit detail about IEC 60601-1-8, you can purchase the official document on the IEC website at www.iec.ch.