Page 135 - Safety Risk Management for Medical Devices

114 Safety Risk Management for Medical Devices

Figure 12.14 Use-Scenario Inventory.

List the potential effects of the Failure Mode. Local Effects may not be visible
from outside the System, but create an internal effect within the System. End Effects
are observable from outside the System.
If the End Effect is a Hazard in the CHL, then the Safety Impact is yes. Else, it
is no.
List all the existing mitigation that serves to prevent the Failure Mode, in the
“Existing Mitigations” column.
Assign ratings. Table 12.12, Table 12.13, and Table 12.14 offer suggestions for rank-
ings of Severity, Occurrence, and Detectability, respectively. Remember that the rat-
ings are inclusive of all the existing mitigations. Let’s examine each rating.
Severity is the significance of the worst reasonable consequence of the End Effect
at the System level. Severity ranking definitions are different depending on whether
the End Effect has a safety impact or not. For End Effects that do not have a safety
impact, use the left column in Table 12.12, and for those with a safety impact use the
right column.
To rank the severity of End Effects without a safety impact, it’s necessary to know
the primary and secondary functions of the item under analysis. For example, if a
Failure Mode causes the complete loss of the primary functions, the severity ranking
would be 4, Critical. Use the information from Section 12.8.3.2 to determine the
Severity ranking.