We don't have synonyms for safer yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are safe, wafer and saver.
(n) :
Initialism of Simplified Aid For EVA Rescue (“a small, self-contained, propulsive backpack system (jet pack) worn during spacewalks, to be used in case of emergency only”).
(n) :
Initialism of Simplified Aid For EVA Rescue (“a small, self-contained, propulsive backpack system (jet pack) worn during spacewalks, to be used in case of emergency only”).