I think you are quoting from the “GP Notebook” web page about section 2. The MHA advice on that website is of low calibre. You can see the correct position by just reading section 2 itself:
(2) An application for admission for assessment may be made in respect of a patient on the grounds that—
(a) he is suffering from mental disorder of a nature or degree which warrants the detention of the patient in a hospital for assessment (or for assessment followed by medical treatment) for at least a limited period; and
(b) he ought to be so detained in the interests of his own health or safety or with a view to the protection of other persons.
I can’t comment on the suicide part of your question but maybe a doctor will read this and reply.