A fire rating is a reference to the level of protection a safe offers the contents against fire. Most ratings are described as a combination of temperature and time to give an accurate and easy to understand indication as to the level of protection provided.
As an example, Dominator Safes have safes that are certified to comply with the CNS Class 350F 105 minute rating. 350 degrees Fahrenheit is the point at which paper will get damaged from heat. With the testing furnace heated up to over 1300F, the internal compartments remained below 350F for 105 minutes.
You can use this information to determine if the provided fire protection is adequate for the intended application.
Many safes carry a “recommended” or uncertified fire ratings. These safes are guaranteed by the manufacturer based on their own design and testing and have not been tested by an independent testing house.
It is important to note that all of these ratings use the burning point of paper as a basis. You would need to look into the burning point/temperature of the particular items you want to protect in order to determine if the rating would provide sufficient protection.