DESIGN OF SAFE MEDICAL DEVICE PROTOTYPES - Design and Development of Medical Electronic Instrumentation - page 98

the construction of a number of useful test instruments suitable for assessing the electrical
safety of medical electronic instruments.

STANDARDS FOR PROTECTION AGAINST ELECTRICAL SHOCK

It has been a long time now that medical electronic devices left the realm of experimentation
and were transformed into irreplaceable tools of modern medicine. This widespread use of a
very diverse variety of electronic devices compelled countries to impose regulations that
ensure their e

cacy and safety. In the United States, the Food and Drug Administration
(FDA) is responsible for the regulation of medical devices. In the European Union (EU), a
series of directives establishes the requirements that manufacturers of medical devices must
meet before they can obtain CE marking for their products, to authorize their sale and use.
In addition, however, individual nations of the EU may impose local regulations through
internal regulatory bodies. Other countries, including Canada, Japan, Australia, and New
Zealand, have their own regulations, which although similar to the harmonized European and
U.S. standards, have certain particulars of their own.
Safety standards are sponsored by organizations such as the American National
Standards Institute (ANSI), the Association for Advancement of Medical Instrumentation
(AAMI), the International Electrotechnical Commission (IEC), and Underwriters'
Laboratories, Inc. (UL), among many others. These standards are written by committees
comprised of representatives of the medical devices industry, insurance industry, academia,
physicians, and other users in the medical community, test laboratories, and the public. The
purpose of creating these broad-spectrum committees is to ensure that standards address the
needs of all parties involved in the development, manufacture, and use of medical devices.
Thus, through a consensus process, emerging standards are deemed to capture the state of
the art and are recognized at national and international levels.
In general, safety regulations for medical equipment address the risks of electric shock,

fi fire, burns, or tissue damage due to contact with high-energy sources, exposure to ionizing

radiation, physical injury due to mechanical hazards, and malfunction due to electromagnetic
interference or electrostatic discharge. The most signi cant technical standard is IEC-601,

Medical Electrical Equipment , adopted by Europe as EN-60601, which has been harmonized
with UL Standard 2601-1 for the United States, CAN/CSA-C22.2 601.1 for Canada, and
AS3200.1 and NZS6150 for Australia and New Zealand, respectively.
According to IEC-601, a possible risk for electrical shock is present whenever an oper-
ator can be exposed to a part at a voltage exceeding 25 V RMS or 60 V dc, while an energy
risk is present for circuits with residual voltages above 60 V or residual energy in excess
of 2 mJ. Obviously, the enclosure of the device is the

fi

first barrier of protection that can pro-
tect the operator or patient from intentional or unintentional contact with these hazards. As
such, the enclosure must be selected to be strong enough mechanically to withstand antic-
ipated use and misuse of the instrument and must serve as a protection against

fi

fi res that

may start within the instrument due to failures in the circuitry.
Beyond the electrical protection supplied by the enclosure, however, the circuitry of the
medical instrument must be designed with other safety barriers to maintain leakage cur-
rents within the limits allowed by the safety standards. Since patient and operator safety
must be ensured under both normal and single-fault conditions, regulatory agencies have
classi fi ed the risks posed by various parts of a medical instrument and have imposed

speci first type of

part is the accessible part , a part that can be touched without the use of a tool. Touching
in this context not only assumes that contact is made with the exterior of the enclosure or
any exposed control knob, connector, or display, but that it could be made accidentally: for
example, by poking a

fi cations on the isolation barriers to be used between di ff erent parts. The fi

fi finger or pencil through an opening in the enclosure. In fact, most