Page 68 - Safety Risk Management for Medical Devices

The BXM Method 47

The BXM methodology uses the architectural design of the System as a road map,
and looks for the Failure Modes of each architectural element. A critical principle in
this method is the strict adherence to the scope, and boundary of analysis within the
FMEAs. This principle allows the performance of an FMEA of a given component
agnostic of the System in which it is used. That is, the FMEA needs to only concern
itself with identifying the End Effects at the boundary of analysis. A great benefit of
this principle is that the analyses of the architectural components can be integrated in
the same way that the physical components are integrated per the System architecture.

10.3 QUANTITATIVE RISK ESTIMATION

Another attribute of the BXM method is the quantitative estimation of risk. See
Section 17.3 for details. Quantitative estimation of risk enables a simple way of evalu-
ating the acceptability of residual risk. It boils down to a simple comparison of two
numbers: the residual risk, and the acceptable risk level. The BXM method uses
Boolean algebra to compute the residual risk of a System: per-Hazard, per-
Hazardous-Situation, and overall.
Thanks to its mathematical approach, the BXM method lends itself to implemen-
tation in software tools. The benefits of use of a software tool in risk management are:
1. Objective and automatic determination of risk acceptability
2. Avoidance of error-prone manual computation/assessment of risk
3. Ability to always have an up-to-date risk assessment
4. Ability to evaluate the safety impact of proposed design changes
5. Ability to reuse estimations of Harm probabilities across multiple projects
6. Ability to compute the overall residual risks of the System (medical device)