In 1941, during the early stages of WWII, researchers at the U.S. Department of Agriculture’s Northern Regional Research Laboratory in Peoria, Illinois were conducting tests on numerous varieties of mold samples to uncover a strain of mold that would best produce penicillin. After a global search, with samples sent from around the world, the most productive strain came from a moldy cantaloupe found at a local, Peoria fruit market. (see The Discovery and Development of Penicillin)
Penicillin, heralded as one of the greatest advances in the history of therapeutic medicine, relies on the growth of mold spores for its production. For valuable items in self-storage, however, the growth of mold spores spells destruction. Mold growth is a relatively common occurrence in an un-conditioned self-storage unit, but it is also something that can be controlled. The growth of mold is often seen in a storage unit that lacks proper ventilation and has damp, stagnant air. Mold growth under these conditions can be controlled once it is understood how it occurs.
To understand how it occurs, however, the first thing we need to do is explain what Dew Point is. Put simply, as a molecule of air cools, it shrinks. A molecule of water does not. Dew Point is the temperature at which a molecule of air shrinks to the point that it can no longer contain the moisture suspended within it. The moisture will then condense in the form of a water droplet on any hard surface. This surface can be anywhere, but is typically seen at the separation point between warmer and cooler air: floors, walls, and ceilings. This phenomenon is readily evident on the side of a cold drink on a warm, summer day. In a building, this is prevented by having an air barrier (so the air cannot pass through from one side to the other) and adequate insulation (to prevent the cold air on one side from conducting through to the warm side, and thus cooling it down to the dew point). In a warm weather climate, it’s the heat penetration from outside that causes the cool, inside air to condensate.
In a traditional, metal storage building (with a metal roof and walls exposed to the inside of the storage unit), the humidity present in the air can condense on the underside of the roof to the point that it begins to drip on the items stored below. While this isn’t as noticeable in a building with an exposed wood roof (as the condensing water droplet is absorbed by the wood), something worse is happening – Mold.
Mold spores are living organisms that require three things for their survival: A humidity level of approximately 50-80%, an approximate temperature of 50-90 degrees Fahrenheit, and an organic food source (wood, paper, leather, etc.) Mold spores can be controlled by simply eliminating one of the three ingredients. As it is not practical (or sometimes, possible) to eliminate the food source, the next best option is to control the level of moisture present. The obvious solution here is to prevent the intrusion of water (via holes, leaks and cracks) into the storage unit, but what about the humidity present within the air itself? Arguably the chief cause of mold on items in long-term storage, excessive humidity is often overlooked in this situation. Controlling the humidity levels in a storage unit is a win-win, as by doing so you both limit condensation and control mold. Additionally, the expansion and contraction cracks seen in the surface of wooden items in storage are typically caused by the moving of the wood fibers as they absorb and release moisture. Controlled humidity means no unwanted cracks in Grandma’s heirloom furniture.
So, while choosing a temperature and humidity controlled environment to store your valuable possessions doesn’t mean the storage unit next to you is without moldy cantaloupes, it does put the odds on your side that penicillin is not growing in yours.