What are fire ratings?

Class 3 is moderate-to-high chance of a fire. Burning permits (depending on your state law) usually are not allowed on Class 3 days. Class 3 usually means it is dry, high winds, and a mistaken fire...

1 hour for single wythe

12" is a good rule of thumb for 2-hour rating....but the 2006 IBC will give you a more accurate indication, plus industry web sites for concrete vendors will give you more accurate info.....

checking your post orders

It means it's got six liters of water in it, so it's good for fighting, say, a wood fire but don't use it on a flammable-liquid or electrical fire.