Page 194 - Safety Risk Management for Medical Devices

Risk Evaluation 173

risk is acceptable. To meet the expectations of public opinion, it might be necessary
to give additional weighting to some risks” [3]. For example, people fear flying more
than driving a car. As such, a large weighting factor has been put upon flight safety.
The FAA sets the acceptable maximum probability of a catastrophic failure per flight
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hour for commercial aircraft to 10 , defined as extremely improbable. To put this in
perspective, if an aircraft flies 10 hours per day, every day, it would take 273,973 years
9
to complete 10 hours of flying.
As a practical means of measuring the public opinion about the tolerance of risk,
it may be acceptable to presume that the concerns of the identified stakeholders reflect
the values of society and that these concerns have been taken into account when the
manufacturer referenced a reasonable set of stakeholders.

19.2 RISK EVALUATION FOR QUALITATIVE METHOD

In the qualitative method, risks are stratified into relative rankings from high to low.
In the example offered in Section 17.1, three ranks of high (red), medium (yellow),
and low (green) were devised.
For Hazards or Hazardous Situations for which applicable international or national
standards can be found, determine residual risk acceptance by evaluation of confor-
mance to those standards. For other Hazards and Hazardous Situations compare the
individual residual risks and the overall residual risk to state-of-the-art. A method for
establishing the state-of-the-art using risk-profiles was described in Section 11.3.1.
In the absence of applicable standards or state-of-the-art information, you may
need to rely on subjective expert opinion to qualitatively judge the acceptability of
risks of your device in consideration of the benefits that it offers.

19.3 RISK EVALUATION FOR SEMIQUANTITATIVE METHOD

Similar to the qualitative method, for the semiquantitative method, strive to use
compliance with applicable international or national product safety standards as indica-
tion of risk acceptance. And, where applicable standards are not available, compare to
the state-of-the-art, or refer to benefit risk analyses.
In the semiquantitative method, we can numerically compare the probability of
occurrence of Harms against the state-of-the-art. However, the severity is not easily
comparable. That is, you could say a particular Harm, e.g., infection, has a severity of
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Serious and could happen with a probability 10 . That fills one cell in the risk
matrix (see Section 17.2 and Fig. 17.2). But the state-of-the-art rating of severity may
not match your severity rating. That is, the manufacturer(s) of the products that
inform the state-of-the-art may have different definitions for the severity classifications
than you do.