Many fungi and bacteria produce serious damage such as decomposition of antique materials. This is as a result of the impact of specific enzymes like cellulasses, proteases, ligenases, and organic acids. Pigmentation and physical damage on materials are other deteriorating effects in addition to bio-deterioration.
Fungi are particularly dangerous because they show a substantive tolerance to environmental conditions. Dispersion of spores is the main cause of contamination in the environment. The spores produce allergies and other illnesses in people and biodeterioration on antique objects. Spores in a dormant state are commonly present in the air and on the surface of objects.
However, it is the moisture content of materials that allows microbial growth. In this context, air ventilation is an easy and safe method to control and stabilize relative humidity, temperature, moisture content and consequently, microbial activity rate.
Over the past 20 years, various air conditioning systems have been installed in buildings to contain environmental conditions and to prevent the development of pathological agents. It has often been found that these systems present a high risk of fungi or bacteria growth and spread, which contaminate aerosols that damage objects as well as human health. In particular, the humidifier components of these systems are favourable to microbial growth.
Some ancient buildings usually in museums and archives present serious conservation problems because of the excessive insulation that is characteristic of new architectural designs. It has been found that sophisticated climate control systems do not avoid condensation phenomenon in some areas of the building, a factor that produces an increase of water content in inappropriate materials such as carpets, wallpapers, paints and new products including plasters and silicon joints. These materials provide ecosystems adequate work using common standards of 50% ± 5%. Relative humidity and 20oC ± 2oC T, and air change/hour CACH) in the range of 6 – 8.
Nonetheless, experimental results have shown that it is not required to maintain these strict standards. This is because to determine correct or incorrect values, many crucial considerations are put into the following perspectives. First is the specific characteristic of the buildings and collections. Second is the use of ancient objects and the evaluation of environmental parameters indoors and outdoors, including ventilations.
To avoid bio-deterioration in museum and archive collections, it should be borne in mind that fungi and bacteria are considered to be human pathogens and therefore included in hazard groups. Having been identified and quantitatively evaluated; measurements of temperature, relative humidity and ventilation rule were recorded over a period of time. A drastic decrease was observed in microbial growth over a period of one year in rooms without a climate control system as a result of stabilization and decrease of relative humidity.
Even after the air conditioning system was installed, there was high relative humidity contamination. This could be attributed to air movement initiated when ventilators were installed and activated. It was observed that increased air movement removed spores from the surfaces of objects and from the walls and spores of the room. If the air flow is taken into consideration, there is a slight increase in microbial activity. This finding could be due to various factors such as the presence of more fungi or bacteria in the storage room, or some other environmental factors.
After the climate control was used for one year, a low amount of accumulated dust was observed. It was thought that after long exposure to the airflow from the air conditioning system, the decreased dust least contributed to a reduction in microbial growth. Also, it was discovered that there was a decrease and a stabilization of microbial development in most of the books and documents exposed to the improved climate including documents kept in boxes. Contamination level depended on the nature and type of materials, including hygroscopicity, location and other factors. In general, microbial development was more variable on the surfaces of books than in the internal pages, and it depended on the moisture content of the paper and condensation phenomenon.
Over the years, fungal contamination of air and paper samples was higher than that of bacteria. Fungi can grow in a range of 60% to 90% relative humidity while bacteria can grow at increased levels of over 85% because they need more water to grow. From experimental results, it was observed that cellulose objects required longer exposure time in the improved climate to achieve a significant decrease on microbial growth such as one month but three months for a significant growth on books. Among identified fungi, many species in the general classes of Aspergillus Penicillium, Cladosporium, chactomium and Trichoderma were found to be very dangerous to antique materials. Particularly, Aspergillus Penicillium and Cladosporium have spores that regenerate at a relative humidity of above 65% and temperature of 220C – 24oC, in a short time period of 24 hours.
In this study, similar fungi and bacteria were identified in air, paper and filter samples, although the quantities were different. Penicillium was the most fungus genus found. It was discovered that when isolated in archives and museums, high levels of contamination were found in environmental and surface samples. There was a significant decrease in the levels of environmental contamination after the introduction of the climate control system. It normally takes a month after implementation of ventilation and three months to detect a decrease in fungal and bacterial activities in surface samples from books and documents.
Variability in levels of contamination after implementation of the ventilation treatment was found in museum storage due to large size of the room, complex geometry and excess of objects. These factors prevent the desired air exchange and create adverse microclimates and ecosystems. Consequently, longer exposure to ventilation was required to achieve stable environmental conditions and low microbial contamination. It is essential to maintain air movement even in a difficult area where ventilating air may not normally reach.
Air circulation could produce significant spreading of spores in the environment. Therefore, continued ventilations with low air flow is recommended. The efficacy of air ventilation depends on the combination of relative humidity, temperature, ventilation rate and exposure time. The number of objects located in square meters, with the nature and state of conservation of the museum pieces, should be considered.
Books should be placed on open shelves rather than on compact shelves. The use of boxes and compact shelves will prevent the deposition of dust on objects, but it can create a microclimate that produces an increase in microbial activity. The creation of an environment without significant fluctuations would increase the maintenance and preservation of buildings and collections. Ventilation and housekeeping are the most preventive measures for archives, libraries and museums, as well as the personnel.
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Abu Lamidi, Chief Conservator, Department of Conservation, National Museum and Monument, Benin City
