Emergency chat can be used in any situation where speech is impossible but communication is still necessary.

The splash screen has a base text that explains to the person you gave your phone to that you can't use speech and want to use this app to communicate. The default text is aimed at people experiencing an autistic meltdown, where their speech centres stay non-functional for a while even after they've recovered.
Both the title and text can be adjusted in the settings screen to be whatever you want the person you give your phone to know.

You can then continue to the next screen which has a simple chat client.