The Hazmat Placards app allows you to quickly look up hazard identifications based on the NFPA safety diamond.
You can also use it as a study tool to quiz yourself to know the values off of the top of your head.
Tap the diamond regions to dial in the numbers and press decode to get hazard details. You can also press and hold a region to see a cheatsheet on values for that hazard category.
If you'd also like the ability to track and map particular hazards, check out Hazmat Placards Plus.
NOTE: We have been alerted to the following correction: the "Reactivity" hazard should be "Instability." This and all other information will be updated according to the most recent NFPA 704 in the next release.