While neither Helium nor Argon will damage tissue (they are both noble gases, and therefore chemically inert), they are dangerous to breathe because they displace the oxygen in the lungs. The brain becomes oxygen deprived and acts like it is drowning, similar to what happens when huffing.
Probably the only safe way to breathe helium (especially for more than one breath at a time)is to breathe the helium oxygen mixtures that deep sea divers use. This is a mixture of ~20% oxygen and ~80% helium that is used at extreme depths. The helium replaces the nitrogen normally found in air, because at high pressure nitrogen can dissolve in the blood, causing nitrogen narcosis and the bends.