Thanks for your question. There is no such thing as a "fire protection rating" for mattresses.

Rather, all mattresses sold in the US are required to pass a fire retardancy test. If they pass, they can be sold to the general public. If they fail, they can't. It's that simple. So as long as you're buying from a credible retailer, you can assume the mattress meets the fire retardancy standards. There are no bonus points or special designations given for being extra flame resistant.

As food for thought, we would add that extremely few fires can be traced to a mattress somehow catching fire. This was true even before the flame tests became mandated by law, and it's even more true now. As such, many people feel that the extra costs (and often chemicals) that are added to mattresses to meet the fire retardancy standards are not justified in the first place.

Net, unless you have a lifestyle that is especially high-risk from a fire persepective -- say, you are a narcoleptic psychic medium who likes to hold candlelit séances on your mattress -- you are probably fine with the fire protection level of any mattress sold in the US.

I hope that helps.