Preventing Mold

In the past, institutions holding paper, leather and parchment collections were urged to maintain 50% relative humidity; 365 days per year. This was done in order to avoid the damage caused by cycles of dryness in winter and high humidity in summer. Very low levels of moisture in the air cause shrinkage and embrittlement in most organic materials. High humidity accelerates the rate of degradation and can cause mold to bloom.

De humidification; in summer is fairly easily achieved with adequate, round-the-clock air-conditioning. But maintaining 50% RH ;in the winter in our area is another matter. It was soon discovered that, unless the building had been designed to be humidified in the winter, the extra moisture pumped in through the HVAC; condensed on windows, walls and collections. In many cases, the moisture became trapped in the walls and caused insulation and timbers to rot. But the most insidious result was often an outbreak of mold;, since the extra moisture stayed in books and other dense objects well into the warm months and was never really eliminated by the air-conditioning.

A safe, low-tech method for preventing relative humidity from becoming so very low in winter is to keep the thermostat at a low setting so that there is a less marked contrast between the indoor and outdoor temperatures. This is not possible in patron and staff areas but is a good option for storage rooms, stack areas and other places where collections are kept.

In the course of the building audit, take temperature and humidity readings in various locations, at different times, on more than one day. Better still would be to keep a record over the course of a year, to see what the highs and lows are in different parts of the building and how much conditions fluctuate from one day to the next and throughout the year. It is important for the library staff to do this even if the institution has a building engineer.

When you have compiled a history of conditions in various areas where collections are housed, study the readings to see if there are wide fluctuations within a space of a few days. This would indicate that the HVAC is shut down or stepped back at certain times or that it is malfunctioning. Take this log to the director of the library or museum and explain that the frequent changes are causing the collections to deteriorate faster and, in the case of relative humidity levels above 60%, putting the materials at risk of a mold infestation. It is then the director's task to convince the administration of the importance of keeping the air-conditioning in good operating condition and running 24 hours per day in collections areas. Modifications may need to be made to the HVAC system so that dehumidification will occur during cool, damp periods when neither the air-conditioning nor the heat might normally come on.

Conditions conducive to mold include:

• humidity over 60% (45-50% for collections that have had prior mold damage)
• high temperatures (over 75 F) during periods of high humidity
• darkness
• still air
• dirt - mold feeds on organic debris in dust

{mosimage}Humidity is by far the most important factor in facilitating mold growth. An outbreak can start in a surprisingly short time, such as over a summer weekend when the HVAC is turned off or down.

Bear in mind that mold is extremely difficult to eradicate from a collection and that items that have been cleaned of mold will become moldy again at much lower RH levels than materials which have never been contaminated . Mold spores get spread thoughout the building by the HVAC. This is why it is important to change filters, clean ducts and keep wet leaves and other debris away from fresh air intakes.

Many people are sensitive to mold to varying degrees and will suffer an allergic reaction to it. This can manifest itself as skin rashes, headaches, fatigue, respiratory trouble and symptons similar to "sick building" syndrome. Most people will eventually become sensitized with repeated exposure and the severity of symptons varies from annoyance level to incapacitating.

If small quantities of moldy materials are discovered, isolate them from the rest of the collection and follow the directions in.  But if the infestation is extensive, you will need a professional recovery company. Preventing mold is easier than getting rid of it.

To gain a better understanding of the relationship between temperature and relative humidity and the long term preservation of paper based collections, consult Barbara Appelbaum's book, Guide to Environmental Protection of Collections.

MONITORING HUMIDITY AND TEMPERATURE

 Inexpensive dial hygrometers are not reliable and they cannot be recalibrated.

Monitoring  testing is available from us at a low cost and is highly recommended; especially for new builds.