90% damage reduction is twice as effective as 80% (compare 20% damage coming through, vs. only 10%). In the same way, 95% is twice as effective as 90%, and 97.5% is twice as effective as 95%, etc. If 100% damage reduction were achievable, you would essentially have an infinite effective HP.
Specifically regarding explosion mines, there's huge red flashing circle - fairly hard to miss, and you have plenty time to move out of the way. You shouldn't be hit by these.