Medical Electronics Time to go Fourth!
The latest international EMC standard for medical electrical equipment IEC 60601-1-2 Edition 4.0 was published in February 2014. This Fourth Edition replaces the Third Edition of the standard and constitutes a technical revision. Pete Dorey, a principal consultant at TÜV SÜD Product Service explains more
T
he date of publication for the European version of EN 60601-1-2 Edition 4.0 has not yet been
announced, but may be in 2017. Once it is issued, the technical content of the EN version will be identical to the IEC version. As EN 60601-1-2 will be a harmonised standard in Europe, either the third or fourth editions will be allowed to meet European Medical Equipment Directives, until the date of withdrawal of the third edition which is expected to be three years beyond the issue date of the Fourth Edition. The situation is set to become more complex, as in the US the Food & Drugs Administration (FDA) will no longer accept declarations of conformity in support of IEC 60601-1-2 Edition 3.0 for all electrical medical devices as of 1st August 2017. Best practice advice would therefore be that manufacturers should now switch to using the significantly updated and revised Fourth Edition.
Immunity test levels The new Fourth Edition introduces major changes to EMC immunity testing. For example, the Third Edition’s use of the categories ‘non-life support’ and ‘life- support’ is replaced by a two environment category approach in the Fourth Edition, which defines the environments as ‘professional healthcare’ and ‘home healthcare’. Within the Fourth Edition, immunity test levels are now also based on the reasonably foreseeable maximum level of electromagnetic disturbances in the environment in which the device is
intended to be used. Consequently this has resulted in some immunity test levels that are higher than those cited in the Third Edition.
Edition Four also introduces a new
requirement for all medical products to be immunity tested against a minimum of 18 discreet radio service bands, at levels ranging from 9V/m to 28V/m. This is well above the professional healthcare severity level of 3V/m for continuous frequency swept immunity, and some test laboratories may not have the equipment to cope with this new requirement. The Fourth Edition also adopts a minimum separation distance of 30cm for portable RF communications equipment, rather than the approach used in the Third Edition, which required the manufacturer to calculate the separation distance for each frequency band leaving the end user of the product with a complex management task to ensure that it was used safely.
For the first time immunity tests are specified according to the ports of the medical electrical equipment or system. The immunity test requirements are therefore specified on a port-by-port basis. At least one of each type of port must be connected during immunity testing. Also, larger, permanently installed medical electrical equipment and systems can now be tested with a wider choice of test location.
Changes to EMC environment definition Previously, the Third Edition cited a single typical healthcare environment. Within this
environment, manufacturers could set their own EMC immunity levels to be tested according to the intended environment in which the equipment would be used. The new Fourth Edition instead specifies the immunity test levels for two of the three specific environments of intended use: 1. The professional healthcare facility
environment (hospitals, offices, clinics etc). 2. The home healthcare environment (homes, residential areas, areas of public access, transport etc). 3. Special environments, such as areas with high powered medical electrical equipment that are used for magnetic resonance imaging.
Test plan
For the first time, the Fourth Edition introduces the requirement for a test plan. The manufacturer, not their test laboratory, is responsible for submitting a test plan. Annex G outlines what the test plan must include. The new standard also introduces the
requirement of a test report. Previously the manufacturer could self declare that they had complied by completing tables one to eight, contained in Annex C of the Third Edition. The Fourth Edition mandates the completion of a test report, the contents of which is outlined in Clause 9.
Risk management
For the first time, the Fourth Edition introduces specific guidance on EMC and risk management. The key issue here is that EMC susceptibility of the product could lead to unsafe failure leading to harm.
In addition to testing to the standard, the risk assessment is intended to determine if other electromagnetic disturbance phenomena could make a product unsafe. This means that risks resulting from reasonably foreseeable electromagnetic disturbances must be taken into account in the risk management process. Annex F provides additional guidance.
32 December 2015/January 2016 Components in Electronics
For example, a risk assessment must consider if the standard separation distance of 30cm is appropriate to how the product will be used, and the tests adjusted accordingly. However, the standard does not detail how the risk assessment process should be conducted, simply stating what should be done, but not how it should be achieved, leaving manufacturers confused as to how they should tackle this. However, the concept of risks to EMC susceptibility is not new. Under the Medical Devices Directive for CE marking, Essential Requirements specifies that devices must be designed and manufactured in such a way as to remove or minimise, as far as possible, risks associated to magnetic fields, external electrical influences, electrostatic discharge and reciprocal interference with other devices. Although this approach will not look at specific defined risks as per the latest EMC standard, it provides a good starting point for any robust risk management process.
Clause 4.1 Note 2 of the Fourth Edition
requires the manufacturer to perform a number of activities with regard to mitigating electromagnetic disturbances, during the design and realisation of their medical electrical equipment or system. These must be documented in the risk management file, which must be made available to the test laboratory alongside the test plan produced by the manufacturer. The risk assessment and test plan must detail the tests to be performed, test levels, operating method, performance monitoring method and performance criteria.
As IEC 60601-1-2 Edition 4.0 is a technical revision there are a significant number of wide ranging changes to the standard’s requirements. This necessitates that manufacturers of medical devices update their approach to EMC, and should follow the requirements of the Fourth Edition now in order to meet ‘state of the art’ requirements.
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