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34 Safety Risk Management for Medical Devices

Figure 8.1 Type of normal use.

8.2 DISTINCTIONS

As defined in Section 8.1, Abnormal Use is: “Conscious, intentional act or uninten-
tional act that is counter to, or violates normal use and is beyond further reasonable
means of user-interface-related risk control by the manufacturer” [14]. Examples
include: reckless use, sabotage, or intentional disregard for safety instructions.
Malice is intentional act with the aim of causing harm. The distinction between
Malice and Abnormal Use is that Malice has the intention to do harm, while
Abnormal Use is recklessness that might cause harm.
Setting aside Abnormal Use and Malice, we are left with Normal Use. Normal
Use includes the Intended Use of the device, i.e., the medical purpose of the device,
as well as other ancillary uses such as maintenance, transport, etc. (see Fig. 8.1). Also
see IEC 62366 [14] Note 1 to Section 3.9 for further elaboration on this concept.
Any Normal Use is subject to Use Errors, which could lead into a Hazardous
Situation.

8.3 USER-DEVICE INTERACTION MODEL

Modeling of human interaction with technological systems helps with prediction of
use errors and has its roots in aerospace and defense for the design of aircraft cockpits
and crew stations. They model the human in three parts:

1. input/sensing
2. processing
3. output

Fig. 8.2 shows a model of the User-Medical Device interaction. In this figure,
there are two possible ways in which a Use Error can lead into a Hazardous Situation.

1. The User enters an erroneous input into the Medical Device, which in turn
produces an output that is hazardous, e.g., User enters the wrong dose on the
UI of an infusion pump.