This substance is clear and colorless, although in certain concentrations it may have a yellow or reddish tinge. As a corrosive acid, it emits a strong, foul odor that could cause respiratory problems if exposed for long periods. This acid can be found in a variety of concentrations, with the most common being 68%. Above 85%, it is considered a fuming acid. The vast majority of nitric acid produced goes into the production of fertilizer for crops. It is mixed with ammonia to create ammonium nitrate, which helps increase crop yields. Other uses for this acid include making explosives, rocket fuel, and certain organic compounds. This substance is highly toxic to humans and must be handled with gloves, a breathing mask, and eye protection. If exposed to the skin, it may cause burns. Vapors produced by the acid can be harmful to the lungs. Nitric acid is not flammable.