Translation:Jeg er redd for heiser.
Why not use av instead of for here?
Can for be ommited?
Yes, but it's a lot more common to use it, so you shouldn't omit it.
Can you say "Jeg er redd mot heiser"?
Before I get any further. Could I just clarify that saving someone from something is 'redd (ham/henne)' and being afraid is 'redd for'. Is that right?