A colourless alkaline gas with a characteristic pungent smell. Ammonia is an important substance in agricultural, pharmaceutical and industrial cleaning environments. It is considered a hazardous substance because of its toxicity at low concentrations and prolongued exposure to even low concentrations should be prevented. Ammonia is measurable with a wide range of colorimetric detection tubes, electrochemical sensors (only suitable for low concentrations: at high concentrations, the expensive ammonia sensor is depleted quickly) and even with PID instruments (suitable and more cost effective at high concentrations as PID sensors are not depleted and are unharmed even in high concentrations of ammonia. This, and their quicker response time, makes PID instruments suitable for ammonia leak detection).