Injection

This is one of the rarer forms of exposure, and is often combined with Skin / Eye Contact.  Injection occurs where a chemical enters the body via a sharp object that punctures the skin and injects a chemical directly into the bloodstream. 

A common example would be an accidental needle puncture in a hospital. It may also happen in an industrial setting where there is hole-punching or injection taking place.  

An example precaution may be to always wear protective equipment when handling sharp materials.