The Organization of Economic Cooperation and Development (OECD) produces a list of High Production Volume (HPV) chemicals. According to the OECD, more than 5,000 toxic chemicals are produced or imported in volumes in excess of 1,000 tons per year in North America. On average, there are about 400 major incidents per year in the United States and Canada involving these chemicals.
Many of the most common toxic gases, including carbon monoxide, hydrogen sulfide, sulfur dioxide, chlorine, ammonia, cyanide, ethylene oxide, nitric oxide, nitrogen dioxide and chlorine dioxide, can be measured by means of compact, substance-specific electrochemical sensors. Gas that enters the sensor undergoes an electrochemical reaction that causes a change in the electrical output of the sensor. The difference in the electrical output is proportional to the amount of gas present.