PREVENT MOLD BY MAINTAINING SAFE TEMPERATURE AND HUMIDITY LEVELS

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.

Dehumidification; 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

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 Section 4. 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. (Section 8)

INSTRUMENTS FOR MONITORING HUMIDITY AND TEMPERATURE

There are several kinds of monitoring devices to choose from. Some make a continuous record on paper, others keep a record of maximum and minimum temperature and RH. Inexpensive dial hygrometers are not reliable and they cannot be recalibrated.

Monitoring equipment is available from Art Preservation Services and other conservation suppliers, instrument companies and electronics stores such as Radio Shack.

Humidity Indicator Cards;are an inexpensive means of monitoring temperature and humidity in research, storage and exhibition areas. They are available from some conservation suppliers and from the Humidial Corporation. (See Section 5, p. 78)

Thermohygrometers; are instruments that indicate temperature and relative humidity. They do not record on paper, but some can show the minimum and maximum temperature and RH sensed by the instrument since it was last set. The small, inexpensive Thermo-Hygro is available at electronics stores and through many catalogs, at prices ranging from $30 to $90.

Another, even smaller, (2"x1"x1/2") thermohygrometer is made by Arten;. This is a dial instrument that can be recalibrated periodically. It also has a set of seven little squares which change color from pale pink to bright blue as the humidity varies. This feature serves as a quick cross check for the dial hygrometer. It is sold by most conservation suppliers.

Psychrometers; are instruments with two thermometers; one has a cotton cover over the bulb. The cover is soaked with distilled water and air is forced past the instrument. Evaporation causes the wet bulb thermometer to read lower than the dry bulb. The two readings are compared to a chart to determine relative humidity. When used according to the directions, they are very accurate. Psychrometers are excellent for recalibrating hygrometers or hygrothermographs. There are three kinds of psychrometers: aspirating, sling or whirling, and digital.

Aspirating psychrometers use a small fan to blow air on the wet bulb thermometer. They are easier to use but are larger and require batteries. Sling or whirling psychrometers are pocket sized and need no batteries. Air is forced past the thermometers by whirling the instrument. This requires some skill. These two types do not need recalibration. Digital psychrometers give quick temperature and humidity readings as well as wet bulb and dew point. They will hold maximum and minimum readings. They should  be recalibrated periodically. Psychrometers are available from instrument companies and from most conservation suppliers.

Hygrothermographs; record temperature on a scaled paper chart that turns as the week (or month, depending on the model) progresses. The pen that records the temperature is usually controlled by a metallic strip that reacts to the temperature of the air. The pen recording relative humidity is controlled by a set of  hairs that expand or contract in reaction to changing moisture levels. They should be recalibrated periodically and may be unbalanced by frequent moving. An instrument with a one month interval is easier to keep up with than one that requires weekly changing of the chart. It is also easier to see general trends on the monthly charts. Instruments with the chart around a cylinder are easier to read than those with circular charts. They are available from instrument catalogs and most conservation suppliers.

Data Loggers are small, digital data recorders. The stored data can be downloaded to a PC with Windows systems and then incorporated into wordprocessing documents or simply printed as spreadsheets. Data loggers can record temperature and humidity as well as many other factors such as light, ultra-violet light;, air pressure, carbon dioxide and others. They are available from many conservation catalogs and from Dickson and Cascade Group. (Section 5)