Can you really check for a car Vacuum leak using Propane?

I think my car has a vacuum leak and i saw a video about checking by spraying around with the engine running and if it stalls that means thats where the leak is at? Isnt it dangerous though? What if you do it with the engine cold? I heard you can also use air intake cleaner but its more flammable. And if it is the propper way to check for a leak, where should i spray and look out for? thanks