Monika Fjaestad

National Heritage Board

A REVIEW OF INDOOR AIR POLLUTION MEASUMENTS AND COUNTERMEASURES IN SWEDISH MUSEUMS

Measurements

It all started in the early eighties. Three lead seals were exhibited in a showcase built of pine wood and lined by jute cloth. The seals had been "conserved" earlier with cellulose nitrate lacquer. A severe corrosion layer was detected on the objects. The conservators began to suspect that the cause of the severe corrosion was indoor organic pollutants. Gunnel Werner, former head of the metal section at the National Heritage Board (NHB), started material tests in collaboration with the Swedish Corrosion Institute (SCI). Metal coupons were exposed to different species of wood and wood based boards in sealed glass containers. Relative humidity, temperature and time of exposure were variables. Some results from her studies were that:

• - elevated relative humidity causes corrosive acids to be released from wood
• - increasing the temperature by only a few degrees greatly accelerates the process
• - old, dry wood contains less acids then fresh wood but at elevated relative humidity and temperature acids are released in larger quantities
• - at relative humidity below 40% no corrosion was detected

A list of non-recommended and a few recommended modern materials was compiled to meet the demand from the museums. Gunnel Werner deceased in 1993. The research was not continued. Unfortunately, only parts of the studies are published. During 1995-97 material tests were conducted when needed. Eva Johansson and Bo Rendahl at the SCI investigated during 1995-97 four types of indoor environments, control rooms at nuclear power plants and paper pulp plants, defence storage depots and historic houses. Measurements of corrosivity and pollution on 42 sites were conducted.

The ISA-standard for classifying corrosive environments in control rooms was compared to the results of the SCI studies. SCI used not only copper coupons but also silver, zinc and iron which gave a more detailed picture of the corrosive factors in the environment. Different corrosion evaluation techniques were compared and the classification system of the ISA-standard showed to be too coarse for the museum environment. Resistance sensors were also used to calculate the corrosion rate.

Diffusive samplers from the Swedish Environmental Research Institute ( IVL) were used to collect SO₂, NO₂, NH₃ and O₃. No organic gases were sampled. At present there are samplers also for organic acids and aldehydes produced and analysed by IVL. The cost of each sampler including the analyse is around 50 Euro. The measurement is given in concentration value integrated over time.

This year we started at the National Heritage Board a national research project called "Neutral materials in museum environments". The aim of the project is to collect results from earlier projects and perform new material tests, to be able to classify modern materials for use in the museum environment in three classes: 'neutral', 'useful' and 'aggressive'. The project will run for 3 years.

We know that relative humidity and temperature have a major impact on the emission of volatile organic compounds, thus we will create different climates in sealed boxes. Organic acids and aldehydes will be collected by the IVL diffusion samplers. If possible, we will trace no observed damage levels at specific climates.

Countermeasures

The Conservation Department at NHB, as the central conservation resource, is often contacted when new museums, storage and exhibitions are planned. New materials and formulas occur on the market. In case of sufficient time the British Museum standard test is conducted otherwise we try to recommend "safe" materials. In some cases, such as in the Gold room at the Museum of National Antiquities and the Museum of Old Uppsala, a ventilation system with cleaned, dried air and positive pressure for the showcases has been installed. In the museum of Old Uppsala the air will also be recycled through gas filters to avoid accumulation of pollutants in the system.