Scientists at IPI developed algorithms called Preservation Metrics which transform measured temperature and humidity data into numerical estimates of collection decay risk. These metrics allow you to accurately and objectively determine how well each storage area is performing for collection preservation, how well one environment is performing compared to another, and how various collection materials are faring in a particular location. The metrics are incorporated into IPI's data analysis tools, including Climate Notebook® software and the www.PEMData.org [1] website. There are Preservation Metrics for chemical decay, metal corrosion, mechanical decay and biological decay. The biological decay metric, which focuses on mold risk, is called the MRF (Mold Risk Factor).
Analysis is based on empirical studies of mold growth on food grains. The philosophy of the model is that there is an optimum temperature for growth and that as the environment gets hotter or colder the growth rate slows down. There is also an optimum temperature for which the least amount of water is required for growth; as the temperature gets higher or lower, the minimum relative humidity required for growth increases. Recognizing that storage environments rarely have constant temperature and humidity conditions, the MRF integrates over time, creating a running sum of progress toward mold germination.
Collected temperature and humidity data is analyzed to determine if environmental conditions promote biological decay, including the growth of mold and mildew. An MRF of 0.5 indicates that mold spores are half way to germination. An MRF of 1.0 or higher indicates that mold spores have germinated in the environment.
The graphs below illustrate the algorithm. The first illustrates four months of temperature and humidity readings, from May to September. The second graph illustrates the mold risk during the same period of time. The highest reading during the period was 3.81 – indicating that mold spores germinated nearly four times. You can also see in the Mold Risk graph that when conditions change, the mold becomes dormant until conditions are ripe for germination again.