The "rotten egg" or "onion" smell that we may encounter when an appliance is turned on is the result of a process called odorization, where a chemical is added to natural gas by the gas company to produce a distinct and irritating odor. This is for the protection and safety of the consumer as an indication that there may be a gas leak nearby. Thus, if a person smells gas in a strange area or for a prolonged period of time, he or she should call the gas company to have the situation investigated.