How do we fix the dangers of adding water to sulphur trioxide

Sulphur trioxide is added to concentrated sulphuric acid to make oleum (H₂S₂O₇), which is then reacted with water to make sulphuric acid again. SO3 + H2SO₄ → H₂S₂O₇ then H₂S₂O₇ + H2O → 2H2SO₄