How safe is vaping without any nicotine ?

As safe as exposing your lungs to chemicals that will overwhelm their ability to filter them out. Lungs are very delicate organs that work best with fresh air. Do not add anything more in order to protect them.

Even if your vape does not have nicotine, it is still poisonous. Nicotine is the addictive substance but not necessarily the most dangerous chemical in tobacco. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, Flu and Covid vaccines.