If you follow the correct procedures of injecting and your aspirate right I highly doubt you will ever inject directly into a vein. Many times ive nicked or gone through a vein which as results in me injecting a small amount of oil into a vein but all what will happen is it will travel to the lungs were you will cough it up. Ive been injecting for over 20yrs and have never injected directly into a vein.