The flush is not a danger, in fact, some people believe that the flush helps detoxification, particularly of fat tissues. Flush = capillaries dilatation, which help blood circulation.
Also, 100mg of niacin is not that high of a dosage.
Example, 200 grams of salmon yield 16mg of niacin. There are certainly even better sources of niacin, I looked at the first thing that came to my mind.
I need about 500 mg to get a flush.
You should never use time-released niacin, which is not as safe as niacin.