This is a quick, free app to look up the four-digit "UN/NA" numbers on the hazmat placards affixed to highway and rail tankers. The chemical names and other information is shown.
The main data is stored off-line, so it is available when there is no network connectivity. There are links to Wikipedia pages and official online information from NOAA in the US.
This app was written for educational purposes only. Though this data is carefully derived from official US government web pages and is believed to be presented accurately, first responders and other life savers should probably rely on hazmat apps from official sources.