The usability failure mode

Recommended protection

Validation

Alerting is unintentionally disabled.

The system might not alert because it is in a special mode, and nobody notices it.

1. A patient is assigned
2. At least one sensor is connected to the patient
3. The patient is in an alarm condition

Functional testing:

Use the Training mode for the testing

Wait for the alarm condition, then make sure that the system provides a salient visual alarm signal.

Risk of alarm failure

If either the visual or sound alarm is disconnected, then the users might know about it only after it is too late.

Initial alarm testing

On connecting the patient to the alarm system, the system should provide a test sound alarm.

A visual alert, visible from all around the patient, should accompany the sound alarm, for testing the visual backup of the sound alarm, and for verification in case that the sound alarm fails.

Functional testing:

1. Assign a patient to the system
2. Connect the sensors to the patient
3. Enable the sound
4. Verify that the test sound is audible and that the visual backup is salient from all around the patient.

Case of sound failure

The international standard suggests that the alarm system may provide continuous information signals, such as heart pulse waveform.

Apparently, the standard concern is about situation of sound failure.

The risks are about the vigilance of the medical staff.

Sound detector

If the alarm system is equipped with means for detecting sound failure, then information signals should be optional.

Functional testing

1. Disconnect the speakers
2. Make sure that the system alerts about the sound failure.

Too weak sound

The sound might be too weak compared to the background noise, and distant users might fail to notice it.

Audibility assurance

The system should analyze the generated sound compared to the background noise and automatically adjust the sound level to an about-optimal signal-to-noise ratio.

A special test control, such as a button, may be used, to always test if the sounds are audible. Alarm-Reliability.pdf

Functional testing

1. Generate a test sound
2. Apply background noise such as by vacuum cleaner operation
3. Repeat the test sound
4. Make sure that the test sound is audible from all around the patient even with the background noise.