'He reached safe.' is incorrect. The noun 'safe' is a Word for a metal strongbox. I don't think that he was reaching for a safe. If he was, then it should say 'a safe' or 'the safe'. The other use of the Word 'safe' is an adjective, a person can't reach for an adjective. The noun form for the adjective 'safe' is 'safety'. A correct sentence is 'He reached safety.' (a safe place).
'Please speak loud.' is technically correct, the Word 'loud' is an adverb but it sounds a bit clumsy. Alternates are 'Please speak loudly.' or 'Please speak aloud.' Both 'loudly' and 'aloud' are also adverbs which can modify the verb 'speak'.
