The most obvious factor can be observed by any amateur at the SLS photo - it looks like two long white thingies strapped to the sides of the rocket :) . Joking aside - Space Shuttle was deemed about as safe as 1 in 60 flights by two different commissions. This SLS uses exact same hardware in general, and can't be much safer than an inherently unsafe Shuttle. That's unfortunate fact of life. I sincerely hope that no crew would be harmed flying this thing.