Most safes may be designed to protect your belongings and important documents from fire and theft, but chances are they aren't waterproof. Even if you don't suffer from flood damage, moisture can still get into your safe, especially if you store it in a damp location. That moisture can lead to mould and mildew damage of the items you are trying to store and protect. There are several ways you can absorb the moisture inside the safe, keeping your items protected from damage.
Lay silica gel packets inside your safe. Silica gel packets, which can be found in craft and hobby stores, as well as in shoe boxes, are a desiccant that absorbs moisture and can be used over and over again. Remove your silica gel packets once a year and dry them in the sun for four to six hours before returning them to your safe.
Place a 1/2 cup of dry rice inside a jar and place the jar in the safe. Rice is known to absorb moisture, and it doesn't contain any harmful chemicals. Replace the rice in your safe every four to six months to maintain dryness inside the safe.
Open a box of baking soda and put it inside the safe. Sodium bicarbonate (baking soda) absorbs moisture and deodorises, an added benefit if you are also trying to eliminate the odour of mildew from prior dampness.
Purchase a calcium chloride crystal moisture absorber such as DampRid or Moisture Absorbent. Calcium chloride crystals draw moisture out of the air and into the crystals, drying out your damp safe. These types of moisture absorbers can be found in the cleaning supply section of most grocery stores.
Place two to three moth balls in a glass and set the cup inside the safe. Moth balls are known to absorb moisture, but also contain toxic chemicals that may be harmful if ingested. Wash your hands thoroughly after handling to avoid accidental ingestion. Moth balls also put off an odour that could penetrate the items in your safe, and some people may consider that smell offensive.