Recently, a reader wrote asking: “Is it safe to store coins in modern-day, small-to-medium-size home safes that are certified fire safe/waterproof/drop resistant to the various levels of protection?”

Interestingly enough, a similar question was asked by a participant in my recent preservation workshop at the 2014 Royal Canadian Numismatic Association convention.

The type of safe one buys is a serious consideration.

Two major types of safes are available: ones that are theft resistant and those that are fire resistant. When deciding between the two you need to consider your risks.

Ask yourself what is the highest risk to your collection — theft or fire. I have found that most collectors feel that theft is the bigger risk.

Readers are likely familiar with the Underwriters Laboratories rating found on safes.

Theft resistance

For security safes, UL tests how long a safe can withstand a burglar.

In its laboratories, UL attacks a safe with a variety of tools commonly used by thieves to open a safe. These include high-speed drills with carbide tip bits, diamond grinding wheels, chisels, pry bars, hammers and saws.

As a result of its testing, UL determines the “Net Working Time” for each safe. This term reflects how long it takes to break into a safe. For example, a safe with a “TL 15” rating requires a net working time of 15 minutes, a “TL 30” rating 30 minutes, and so on.

The higher the rating, the safer the safe. “TL 30 x 6” refers to a safe where all six sides of the safe were attacked.

A “TRTL 30” rating designates a safe that successfully resisted 30 minutes of net working time with a torch as well as the tools already noted.

Fire resistance

A fire-resistant safe is designed to withstand high temperatures and protect the items stored within. They are also often engineered to be impact resistant, i.e., they can survive being dropped from a considerable height.

The impact resistance is considered because, during a fire, floors burn and collapse, taking the contents down with them.

UL tests fire resistance by heating a safe to an external temperature of 1,500 degrees Fahrenheit and then measuring how long it takes for the interior temperature to rise to 350 degrees Fahrenheit.

It chose 350 degrees Fahrenheit because paper begins to char over 400 degrees.

A safe with a “Class 350 1/2 hour fire rating” will maintain an internal temperature of less than 350 degrees Fahrenheit for a half hour.

For impact testing, UL heats the safe up as it does with fire testing and then drops the safe onto concrete rubble from a height of 30 feet. It then turns the safe upside down, reheats it, and drops it again.

Throughout this testing, the safe must maintain its integrity and protect its contents. A safe with a “Class 350 1 hour fire and impact” label will have passed both tests and protect the safe’s contents for one hour.

Although good at protecting their contents from fire and impact, fire and impact resistant safes are not very theft resistant.

Another downside of fireproof safes is that the interior often feels damp. Collectors have complained that papers stored inside these safes smell musty. This is due to the insulation used. Some fireproof safes are insulated with what is referred to as a “wet insulation.”

Commonly, this is a mixture of Portland cement, diatomaceous earth, glass fibers and vermiculite. As this mixture cures, the vermiculite and diatomaceous earth absorb and retain any of the moisture. In the event of a fire, they release it as steam. The moisture inherent in this kind of insulation creates the damp interior. As such, fire safes are not usually recommended for storing collections, since the higher relative humidity can lead to mold and corrosion.