3 ms·Odorless / colorless -- same as natural gas. Just drop in a tracer chemical.by boringg 5y agoOdorless / colorless -- same as natural gas. Just drop in a tracer chemical.barrygwn 5y agoUnfortunately, these tracer chemicals tend to poison the fuel cells in cars. So that is not an optionboringg 5y agoSurely there is a tracer chemical that could work.HPsquared 5y agoThe usual ones are sulfur based.