How does 'Om Mani Padme Hum' protect us from danger? 'Om Mani Padme Hum' (translation: 'Hail the jewel in the lotus') is a six syllable invocation (mantra) of Avlokitesvara, one who is invoked as the Protector from danger.
Does it mean protecting from danger as purifying :


Om (Pride / Ego)
Ma (Jealousy / Lust for entertainment) 
Ni (Passion / desire), 
Pad (Ignorance / prejudice) 
Me (Greed / possessiveness), 
Hum (Aggression / hatred)
I'm going to try to answer your question by equating "danger" with Mara (devils).
Buddha used Mara both literally and figuratively, such as gods in heavens who hold wrong views, 5 skanda, attachment to sensual pleasures etc.  He said meditation from 1 first Jhanna is a safe place to hide from those dangers.  

However, if danger in a sense of things happen to you like car accident, danger from natural disaster, sickness, aging, and causes of death, nothing can help for those are the way it is and from Karma.