Biomedical Engineering Reference
In-Depth Information
operating and maintaining system to achieve acceptable risk within the timing and
cost constraints in the system life-cycle [
56
]. Hazard analysis can improve the safety
that defines real or potential conditions that can cause injuries, illness, loss of sys-
tem, property or damage environment.
2.2.3 Safety vs. Reliability
As a conventional approach, it is assumed that a reliable system is safer and vice
versa. However, it is not always true and it can lead to a lot of confusion to analysis
a system failure. Actually, it is often true that the safer system can be less reliable.
For example, an inoperative elevator can provide maximum level of safety. The
inoperative elevator cannot do any functionality like opening or closing the door,
moving up or down, after pressing any button. To use the elevator, in this state is
always safe, but the reliability of the elevator is zero. The inoperative elevator has
not any functionality, it is absolutely unreliable and ineffective to use for moving
up or down to different floors. To improve the safety of a reliable system, system
designer introduces some elements to add the functionalities. Such as, designers can
introduce elements and controls for moving up or down of the elevator. These new
elements can reduce the reliability of the elevator. Such that, a sensor can provide a
proper opening or closing door operation. If the sensor is out-of-order, then the ele-
vator will not move. Here, the sensor behaviour reduces the reliability and increases
the safety of the system.
1
Reliability and safety are the main attributes to determine effectiveness of a sys-
tem, where effectiveness is influenced by the life-cycle activities related to the de-
sign, manufacturing, use and disposal of the product [
22
]. IEC 60513 [
50
], fun-
damental aspects of safety standards for medical electrical equipment, provides a
safety standard for developing the medical systems that assures the basic safety and
essential performance. IEC 60601 [
52
] address reliability stating that “
reliability of
functioning is regarded as a safety issue (for life-supporting equipment) and where
interruption of an examination or treatment is considered as a hazard for the pa-
tient
.”
According to the FDA [
33
] regulation safety is defined as: “There is a reasonable
assurance that a device is safe when it can be determined, based upon valid scien-
tific evidence, that the probable benefits to health from the use of the device for its
intended use and conditions of use, when accompanied by adequate directions and
warnings against unsafe use, outweigh any probable risks.” Effectiveness is defined
thus: “There is a reasonable assurance that a device is effective when it can be de-
termined, based upon valid scientific evidence, that is a significant portion of the
target population, the use of the device for its intended uses and conditions of use,
when accompanied by adequate directions to use and warnings against unsafe use,
will provide clinically significant results” [
94
].
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