Accurate measurement of the respective relative humidity levels interior and exterior is essential for this strategy to be successful. The climate within an individual showcase or cabinet can be controlled if material particularly sensitive to high relative humidity levels is to be stored or displayed. Orange self-indicating silica gel can be used for this purpose. Do not use the blue self-indicating silica gel as the cobalt chloride colouring is considered to be carcinogenic.
It is important that any silica gel used in display cases is conditioned to the desired relative humidity level prior to being placed in the storage or display space. This process is best left in the hands of conservators as there is a risk of too much moisture being absorbed, resulting in desiccation of vulnerable objects.
Commercial conservation materials such as Art Sorb are also available. They are very useful in helping to control relative humidity levels in display cases and similarly sized containers. Art Sorb is available in pellet, sheet or cassette form, depending on the nature of the space in which it is to be used.
Zeolite pellets may be of use in climatic areas in which the endemic relative humidity is naturally high Australian Library and Information Association A Japanese researcher has developed a treated natural zeolite pellet capable of absorbing and releasing large amounts of water vapour.
The pellets have been combined with Japanese paper with the resultant material being produced as a sheet or a paper-covered honeycomb board filled with pellets. Incorporating these materials in storage and display cabinets will minimise relative humidity fluctuations. Zeolites have the added advantage of being able to absorb odours and as such, have been manufactured and sold commercially in packet or bag form for use in the home. They have been used to lower the relative humidity and absorb odours in refrigerators.
If contemplating the use of these products always check their effect in the space in which they are to be used. This is important so that the risk of desiccation, or even inadequate dehumidification, is minimised.
An alternative way of controlling relative humidity levels is to incorporate other materials that absorb moisture, such as treated wood, paper and textiles in the cabinet or display case with the moisture-sensitive artefacts. These water-absorbing materials reduce relative humidity fluctuations by taking up or releasing moisture as conditions change. In this way the artefact is subjected to smaller relative humidity variations. Materials used in this way must be compatible with the moisture-sensitive object.
It would not be appropriate for instance, to store a lead object in an oak box or to use alkaline-buffered acid-free tissue paper with leather objects. In Japan this type of approach is used to deal with the naturally high humidity experienced in that country. Objects are stored in wooden chests in wooden buildings to take advantage of the natural moisture-absorbing and releasing properties of wood.
In this way the box contents are buffered against both the naturally high relative humidity and against any changes in external conditions. This approach would not be suitable for all material types however, especially those sensitive to the acidic vapours given off by wood.
With the right choice of wood hoop pine for example and wrapping of artefacts in acid-free tissue, this approach may allow some of the problems associated with endemically high relative humidity conditions to be overcome without the need for more costly and active intervention. Alternatively, if passive methods such as those outlined above are not sufficient, this problem may be tackled by lowering the relative humidity of the storage or display area itself.
This can be achieved by employing a thermostatically controlled refrigerant dehumidifier to remove excess moisture. As mould formation is encouraged by conditions of high relative humidity, warm temperatures and stagnant air, it may be necessary to employ a combination of dehumidification, air circulation and temperature control.
Refrigerated air coolers can remove moisture from a building or room by condensing it outside. Water collected by this process is pure enough for use in the sling psychrometer.
If the heat index is very high or the wind chill index is very low, then we must take safety measures to protect our bodies from possible effects of the weather, including heat exhaustion, sunstroke, and heat stroke in the summer, and frostbite in the winter.
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Relative humidity matters in a variety of industries for many reasons. Humidity and temperature must be exact in a cold storage facility to ensure items are preserved appropriately.
Whether storing food or chemicals, keeping consistent humidity levels is key to preventing ice buildup and damage to equipment and stored goods. This is why the flu season in the US coincides with the onset of winter. CDC researchers tested the effect of RH on the capacity of the virus released in a simulated 'cough' to re-infect cells. Most of this inactivation occurred within the first 15 minutes of the viral particles being released in the high-humidity condition.
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