Indoor air pollution has been investigated in campaigns time to time in Swedish museums. Metal coupons have always been used to detect the total impact of pollution. The Swedish Corrosion Institute has developed a standard procedure for production and analysis of the coupons. Most of the earlier tests have been executed in outdoor atmosphere, consequently the classification steps are wide and few. Usually the standards ISO 9223 and ISA S.71.04-1985 were used also for classification of indoor atmospheres. A new ISO standard is under development useful even to museums.
This spring the National Heritage Board started an exposure campaign on ten sites using SCI- coupons of carbon steel, copper, silver, zinc and lead. The content of organic acids and aldehydes are measured with passive samplers, particles are collected and the temperature and RH are monitored. The test station is placed in cupboards, showcases, storerooms and exhibition halls. The objectives are to investigate the range of effects, to provide the conservators with a classification of their museum environment and to propose countermeasures.
At many museums in Sweden, the conservators, if any, are aware of the importance of controlling temperature and relative humidity. Often in the newly built exhibitions the ventilation system is under control, in the older rebuilt museums the system needs a kick, now and then, and in the ancient low frequented museums the staff believes in resurrection and eternity. In the last case you will probably find an abandoned thermohygrograph in a dusty corner.
Indoor air pollution is, even if you can sometimes smell it, an invisible ghost to many museum directors. There are seldom dramatic evidence, showing the existence of the pollution. The changes are slow but often uncurable. Now and then strange, anaesthetic changes occur. The first questions are usually - Is it poisonous? Or Is it mould? To be able to analyse the situation we need easy, inexpensive tools to assess the environment onsite, indicators - sensors which give us the clue for further investigations. When damage occurs, eventually, the problem will end up in our hands.
At the National Heritage Board, we started in 1999 a four year research project to enlighten the risk of indoor air pollution. It is called Neutral Materials in the Museum Environment. We follow three main roads:
At an early stage we got in touch with the Swedish Corrosion Institute (SCI) and their earlier survey of corrosive indoor environments. They have the best practice of producing and weighing metal coupons for corrosion tests. Silver strips are used to evaluate the air quality in ventilation systems in general. Monitors like the On guard micro crystal balance and resistance measurements are also available. We chose to follow the SCI method with some modifications. To detect the total range of pollutant's carbon steel-, copper-, silver-, zinc- and lead coupons are exposed.
As a member of the atmospheric corrosion committee at SMS, the Swedish standardising committee, I follow new standards in development. ISO/WD 118 44 is a work document on classification of corrosivity of indoor atmospheres. In November it will be circulated. It contains the SCI methods among others.
Classification of environments
The standard under development has three parts:
Part 1. Determination and estimation of indoor corrosivity. The determination of corrosivity is based on measurements on standard coupons of silver, copper, zinc and carbon steel. Mass loss or mass increase is used to determine the corrosivity category for each metal. This is the first step to classify the environment. The estimation of corrosivity is based on climatic influences, the quality of the building and risk for pollutants, etc.
Part 2. Determination of corrosion attack in indoor atmospheres.
This part contains the standard production of the metal coupons. Also methods of measuring mass loss and mass increase and the calculation of the corrosion rate.
Determination of corrosion rate by using catodic reduction and resistance measurements are also described
Part 3. Classification and measurements of environmental parameters affecting indoor corrosivity.
When the corrosivity is too high for the activity in the location, this is the next step.
This part contains sampling methods for pollution measurements and reagents to use for active and passive samplers.
A tool for preservation
The standard can become a useful tool, with some modifications to predict future damage to museum collections. It will also hopefully be useful to provide evidence and arguments for better materials for interior fittings and filtration/ventilation systems.
The metal coupons indicates which pollutants are present and the specimens can be analysed by weighing and by scanning electron microscope. The indoor source has to be found and removed. A good particle and gas filtration system will remove the contaminants from outdoor sources.
The test stations
In our museum survey we have set up 12 stations.
At each station we expose carbon steel, silver, copper, zinc and lead coupons, passive samplers for aldehydes and organic acids, loggers for temperature and relative humidity and a particle sampler. To build bridges between classification and material tests we also expose lead coupons.
Six stations are located in shelves, cupboards in store rooms, three are placed in show cases and one in an exhibition hall. In some situations there is a controlled climate and in others the ventilation includes gas filtration and some have no ventilation at all. The exposure time for the metal coupons will last up to six months but the samplers are collected after one month and analysed by the IVL (Swedish Environmental Research Institute Ltd). With a six month's exposure we can co-ordinate our results with those of the SCI survey. One year exposure is too long for practicable use. Three months would be optimal.
In comparison with the standard we fear that most of the museum environments will be found in the class of very low corrosivity, the step IC1. We think that a mass increase up to 70 mg/m3 (carbon steel) in one year is too high for museum collections. Maybe the half of the step IC1 will be the limit for a preserving museum environment. It must be taken into account that other materials in the collections are differently affected by the pollutants and have different demands on the environment. Next year the results from the survey will tell their story.
Johansson, E. 1998. Corrosivity Measurements in Indoor Atmospheric Environments - A Field Study, Licentate Thesis, Department of Materials and Engineering, Royal Institute of Technology, Stockholm.
ISO/TC 156/WG 4 - N 338Rev. ISO/NP 11 844, Corrosion of Metals and Alloys, Classification of Corrosivity of Indoor Atmospheres.
National Heritage Board / Riksantikvarieämbetet
114 84 Stockholm
Fax: +46 8 6614277
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