The bound morpheme non is the negator for life-threatening here, so 'life-threatening' is more coherent. This does not come across with nonlife-threatening, which would seem to imply a threat to non-life. Except non is not an english word, it is a prefix of latin origin.

British rules differ, and … Outside official knowledge. Normally when i want to point something that is outside the approval of the company or a government or any entity (for instance, non-official statements, non …