Example of the type of accident in which the SRS curtain airbag will basically not deploy.

The SRS curtain airbags are not basically designed to deploy if the vehicle pitches end over end.
See also:
Brake booster
The brake booster uses engine manifold
vacuum to assist braking force. Do not
turn off the engine while driving because
that will turn off the brake booster, resulting
in poor braking power.
...
Vehicle Dynamics Control OFF mode
This mode allows only the ABS control.
This mode should be used in an emergency situation such as getting out of snow or mud.
When the switch is pressed for more than approximately 3 seconds during ...
Checking the fluid level
Check the fluid level on the outside of the reservoir. If the level is below “MIN” level mark, add the recommended clutch fluid to “MAX” level mark.
Use only clutch fluid from a sealed container.
...
