Monitoring Environmental Conditions in Museums, Galleries and Archives

Data loggers can be a useful tool in monitoring the environmental conditions of historic, sensitive and valuable items in museums, art galleries, archives, historic buildings/sites and other conservation areas.

An important part of maintaining a stable environment for such unique material is accurate temperature and humidity monitoring of the conditions that can affect them. Using data loggers not only helps ensure the long term safety and preservation of artefacts/materials on display and in storage, but can also help with museum accreditation purposes.

Damage linked to RH and temperature fluctuations

Humidity levels are frequently associated with an increased probability of mould growth, mildew, insect pests and other forms of deterioration. Fluctuations (seasonal and daily) tend to be more damaging than constant levels. Different items respond to temperature and humidity fluctuations in different ways, some are more susceptible that others. Variation in relative humidity can loosen furniture joints, cause paint to chip from canvas and damage paper. It can lead to chemical reactions: metallic objects such as tools, coins, medals, cutlery, trophies, etc, are prone to corrosion or developing a patina and would degrade if frequently polished. Many dyes will fade, and even glass and mineral collections can be damaged. Materials such as photographs, documents, leather and fabric may also be particularly susceptible to mould or decay.

Temperature is directly linked to RH and so can aggravate damage by that means. Increased temperature can accelerate the rate of degradation in objects. In some cases high temperatures can soften materials and low temperatures can cause them to become brittle.

Monitoring using data loggers and data interpretation

Using data loggers to provide definitive information about temp/RH conditions can help identify measures needed to achieve a controlled environment and establish an informed preservation strategy. Using loggers to record accurate information about conditions over time is much more effective for building comprehensive profiles than manually taking spot readings, which may not be possible for example at night or during periods of seasonal closure.

It is important to measure temperature and humidity at key points throughout a site as environmental conditions may vary. Data loggers should be positioned to avoid putting them on the floor, near a heat source, near a humidifier/dehumidifier or beside a door or window. Loggers can be set by the user to take readings as frequently as required. To be effective, ideally a monitoring program should be carried out over at least one change of seasons. For smaller museums, monitoring may be particularly important over the winter months if the museum is closed and unoccupied.

Data recorded from the loggers can be analysed to help evaluate the performance of heating, ventilation and air conditioning systems, which can be an important factor in ensuring the optimum conditions for preservation. It can provide data to assess the need for dehumidifying equipment. Data analysis can also help pinpoint fluctuations in conditions with a view to identifying possible causes. For example a rise in humidity may be due to rain, visitors with wet coats in the galleries, open doors, a leaking roof, mopping of floors etc. People also have a significant effect on the environment, raising the temperature and increasing the relative humidity in popular areas.

Recommended guidelines - relative humidity

According to Aim (Association of Independent Museums), current recommendations are to maintain as stable RH as possible within a 20% band. This allows for annual seasonal changes in humidity and the needs of a mixed collection. Commonly used bands are 40%-60% or 45%-65%. Acceptable levels may depend on what is achievable in individual museums and that which best suits the needs of the particular items in the collections. Some, such as archaeological metals, may require more tightly controlled RH level.

Recommended guidelines - temperature

AIM highlights the importance of maintaining stable temperatures rather than allowing them to fluctuate, as this causes greater damage to the collections. Museums are generally heated to human comfort levels of around 17-21°C. Stores can be kept at lower temperatures to slow down degradation of objects (say around 12-15°C).


AIM Focus Paper 'Basic Conservation and Environmental Monitoring', AIM, October 2006

'Monitoring Temperature and Humidity in Museums', Museums Galleries Scotland, April 2003/March 2009

'Managing the Museum Environment', Chicora Foundation Inc. 1994

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