Ethyl mercaptan, also known as ethanethiol, is an organic compound (liquid at room temperature) with a strong, unpleasant odor. It is often added to propane, butane, or liquid petroleum gas, which are otherwise odorless, to make it easier to detect gas leaks. It is flammable, and in high concentrations, it acts as an irritant to skin and mucus membranes. At lower concentrations, it is less immediately toxic, but the odor can cause nausea.
When ethyl mercaptan comes into contact with skin, eyes, or mucus membranes, it can cause severe irritation, pain, and redness. In the case of accidental contact, the affected areas should be washed thoroughly, and any clothing contaminated with the substance should be removed. Ethyl mercaptan may also be absorbed through pores, and should therefore be removed from skin as soon as possible.
When ingested or inhaled, in addition to irritation of the membranes of the lungs and digestive tract, ethyl mercaptan may cause headaches, nausea, fatigue, muscular weakness, convulsions, and liver and kidney damage. Ethyl mercaptan may also cause narcotic effects, including loss of consciousness, respiratory depression, and cyanosis (decreased oxygen levels in extremities, causing lips and/or nails to turn a bluish color). In case of ingestion, do not induce vomiting. Instead, rinse mouth, administer a glass of water, and seek immediate medical attention.
Ethyl mercaptan is extremely flammable. It should be kept away from heat or open flame. When in gaseous form, it may form an explosive mixture with air. As it becomes a gas above 95 degrees Fahrenheit, it is advisable to keep it below that temperature at all times. Fires involving ethyl mercaptan should be extinguished with carbon dioxide or other powder-type fire extinguishers.
Ethyl mercaptan may also react violently with oxidizers such as household bleach and hydrogen peroxide. Calcium hypochlorite will cause particularly strong reactions. Reactions with bleach may convert ethyl mercaptan into compounds that lack its distinctive odor. It will also react with rust, and with strong acids.
While hazardous in high concentrations, in the concentrations in which it is generally present in propane and butane, ethyl mercaptan is not likely to pose any significant additional risks as compared to those substances on their own. Its odor is detectable at a concentration of 0.26-0.97 parts per billion, and it becomes hazardous at more than 1,000 times that concentration, meaning that the amount needed to impart that odor to another substance is very small.