Temperature ratings:
The average house fire is 1200° F
The U.L. (Underwriters Laboratory) fire rating includes temperature and time.
One-Half Hour Rated Products - The furnace is heated up to 1550F over a one-half hour time period.
A Class 350° F means the internal temperature cannot exceed this temperature over the rated period and temperature.
30 minute                 - 1550°F
One-Hour Rated Products   - 1700°F
Two-Hour Rated Products   - 1850°F 
Three-Hour Rated Products - 1920°F 
Four-Hour Rated Products  - 2000°F

Class 350 - Paper which burns at 451 degrees F
         These keep humidity at less than 85% also
Class 150 - Microfilm, microfiche and computer data tapes
Class 125 - Developed for floppy disks.
      The electronic storage media of today like CDs and DVDs
      can safely withstand a temperature of up to 350 degrees.
350, 150 and 125° rated safes all use the same external temperature/time values.
See:
Best Fireproof Safe - Fire Rating | Jen Reviews

 Safe Ratings & Certifications | Water & Fire Rating

Paper:
To properly store paper documents, you need a fireproof box with a temperature UL rating of at least 350° for 60 minutes. A rating of 350 and 60 minutes means that the inside of the fireproof box will not rise above 350 degrees during a fire reaching temperatures of 1,700 degrees lasting 60 minutes. Paper burns at 451 degrees, so you want the 350 rating for paper protection. If you live in an urban area close to a fire station, you can probably get by with a 30-minute fireproof box.
Source: Reader question: Fireproof storage, part two - Unclutterer

In a test with a fire dept. training burning, The small fireproof box was hard to find, but once they pried it open, not only was everything intact, but the CD still worked.
See: Fireproof boxes - do they work? - KFVS12 News & Weather Cape Girardeau, Carbondale, Poplar Bluff

Media and Electronics:
See:
Sentry® Safe allows you to select what you want to protect and selects the correct safe.
They say a 1/2 hour fire chest is ok for media and electronics. They don't list the temperature class, but I assume it is 350°, which is the normal standard.

Seagates non-operating temperature range -40 to 70 degrees Celsius (-40° to 158°F)
A WD Solid state drive (SSD) is rated to 120°C (248° F).

Wire insulation limits are 75-90° C (167-194° F). See wire knowledge | USAwire-cable.com

At temperatures between 120 and 180 degrees can create humidity that will corrupt or destroy data. To store data, look specifically for a media/data safe, or any safe that will keep the internal temperature below 135 degrees and humidity below 85%. (DependableSafes.com)
You can also put some desiccant bags in the safe to keep things dry.


Size:
Letter size: 8.5 x 11 (envelope 9.5 x 12.5)
Legal documents are 8.5" x 14" (envelope 9.5 x 15 or 11 5/8-x 15 1/8").
ISO paper size
A3 11.7 x 16.5 in
A4 8.3 x 11.7 in

Products:
Manufacturer Honeywell Honeywell First Alert SentrySafe SentrySafe SentrySafe
Model 1104 1106 2040F 1170 1200 2300
Where Amazon Walmart Amazon Best Buy Target Staples
price $86 $64 $135 $70 $20 $80
Size (cuft) 0.38 0.6 0.14 0.2 0.27
external dimensions 19x17x7 16x12.5x13 16x13x12.5 15.3x13.6x12 14.3x11.2x6.1 15.4x14.3x6.6
internal dimensions 14.8x12x3.8
Legal, Letter, A4
letter, A4 12x10.4x8.5 12x7.5x3.5 12.8x8.5x4.4
A4
Weight 56 lbs 50 lbs 62 lbs 28 lbs 13 lbs 33 lbs
UL class 1-hour 350°? 30 min 350° 30 min 125° 30 min 30 min 1 hr

Note 1: Most include a 24-48 hr waterproof seal.

Note 2: Most of these list the external temperature and time e.g. 1550° for 30 min for protection, but only one (the First Alert 2040F, which has a 125° rating) listed the internal temperature, which is the critical factor. There are three standards for internal temperature (see above).
Most have 1 1/2 inch thick walls. One of the 30 min. models had 1.3 inch walls. A 1 hr box had 1 7/8 inch chick walls.

SentrySafe QA0121 ($62) allows you to attach an external USB 2.0 2.5 inch HDD/flash drive inside the protective enclosure while accessing it via a usb port located on the outside of the enclosure. Includes 10 CD/DVD sleeves organizational divider. 30 min. protection.



Others:
Amazon.com: fireproof security boxes
The Best 8 Home Safes Reviewed Wall, Gun, Lock Box and Depository Type
Security Safes | Home Safes for Sale, Fire Safe Boxes | Staples®
Best Fireproof Safe | Jen Reviews

Terms:
ETL - Electrical Testing Labs (founded by T. Edison) now Intertek
RSC - Residential Security Container
UL - Underwriters Laboratory

Construction:
I couldn't find much about construction.
Many use flame retardant ABS plastic and concrete, drywall or fiberboard for insulation.
The insulation contains moisture which absorbs a lot of heat in the process of vaporization during a fire.

Placement:
Remember that all fireproof safes will have a moist lining to protect them, so if you are drilling a hole into the safe to attach it to the wall, or for whatever other reason, you would allow the moisture to evaporate out over time, thus compromising the fireproof properties of the safe.

In case of a fire the floor below a safe may collapse, so consider that in placement.

Links:
Top 10 Things We Recommend before Buying a Safe - The Safe House Nashville, TN
National Institute of Standards and Technology (NIST) Care and Handling of CDs and DVDs - A Guide for Librarians and Archivists
Safe - Wikipedia, the free encyclopedia
5. Conditions That Affect CDs and DVDs Council on Library and Information Resources
FireKing Safe Ratings & Certifications | Water & Fire Rating

last updated 10 Aug 2016