7.18.1 - Introduction
There is no section 610 in BS 7671, although
the intention is that it should be reserved for medical
locations and associated areas. The following is thus based
on Chapter 9 of Guidance Note 7, which in turn depends on
draft lEG Publication 364. The draft standard excludes medical
electrical equipment, which is covered by IEC 601-01 : 1988
or BS 5724 : Part I: 1989 and BS EN 60601-01. There can
be little doubt that before long this material will become
part of the Regulations. Medical locations are often hospitals,
but may also include private clinics, medical and dental
surgeries, health-care centres and dedicated medical areas
in the workplace.
The use of medical electrical equipment
is split into three categories:
1. - Life-support: infusion pumps,
dialysis machines and ventilators;
2. - Diagnostic: X-ray machines,
magnetic resonance imagers, blood pressure monitors, electroencephalograph
(EEG) and electrocardiograph (EGG) equipment;
3. - Treatment: surgical diathermy
and defibrillators,
This equipment is increasingly used on
patients under acute care. Supplies to it require enhanced
reliability and safety, as well as measures to reduce electromagnetic
interference.
Shock hazards are covered in
{3.4} and indicate that currents as low as 10 mA passing
through the human body can result in muscular paralysis
(an inability to move) followed by respiratory paralysis
(an inability to breathe). At about 25 mA ventricular fibrillation
(loss of normal heart muscle rhythm) may occur and may be
fatal.
The impedance of the human body (see
{3.4.2}) may be considerably reduced during certain
clinical procedures. For example, the skin resistance is
reduced during surgery and defensive capacity either reduced
by medication or removed altogether while anaesthetised.
Special hazards occur during heart surgery, where electrical
conductors may be placed within the heart , or with the
use of conductive catheters. Under these conditions currents
as low as a few tens of micro-amperes may well result in
death.
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