The Performance of Showcases ; Air Exchange Rates and Pollutants (part I and II)

Hubertus A. Ankersmit¹, Maarten van Bommel¹, Andrew Calver², Frank J. Ligterink¹, David Thickett³ & Simon Watts⁴

Netherlands Institute for Cultural Heritage ¹
Museum of London, United Kingdom ²
The British Museum ³
Oxford-Brookes University, United Kingdom ⁴

Conservators and curators from time to time will have to decide on the design of new showcases or the implementation of measures to improve existing showcases. Sometimes cases have to be air tight in order to prevent penetration of harmful components from the external environment. In other situations a certain level of ventilation is preferred in order to avoid the accumulation of harmful components emitted either by objects or construction materials from the interior of the case. In relation to air tightness and ventilation of showcases the air exchange rate is thought to be the single most important measure of showcase performance. Although air exchange rate measurement services based on tracer gas decay are commercially available in the UK, the service costs in the region of £800-£1100 per test making it prohibitively expensive for routine use, or for research where many measurements are required. In this cooperative study exchange rates and inside/outside ratios of pollutant levels for various showcases have been determined at various locations. The results of this joint research will be presented in two separate lectures:

In Presentation I equipment and procedures of the tracer gas techniques used in this study to measure air exchange rates of showcases will be presented. An important outcome of this research has been to provide an affordable technique for measurement of air exchange using readily available nitrous oxide or carbon dioxide data loggers that can be used to monitor performance of display cases during and after construction. All the equipment is available off the shelf with limited modification and can also be used to test complete cases containing objects and storage enclosures, boxes and drawers for pollution monitoring studies. No external power or monitoring ports is required and the low cost gas delivery method developed makes the system portable - thus equipment can easily be shared between institutions.

In Presentation II we will elaborate on the interpretation of (semi) exponential tracer gas decay curves and the subsequent calculation of air exchange rates from tracer gas decay curves. Measured air exchange rates for several showcases will be compared with measured inside/outside ratios of several pollutant commonly associated with object damage hydrogen sulphide, acetic and formic acid, and dust.

Slides from Presentation I

Slides from Presentation II

Authors to whom correspondence may be addressed:

Presentation I	Presentation II
Andrew Calver	Frank Ligterink
Museum of London	Instituut Collectie Nederland
150 London Wall	Gabriel Metsustraat 8
London EC2Y 5HN	1071 EA Amsterdam
United Kingdom	The Netherlands
E-mail: ACalver@museumoflondon.org.uk	E-mail: frank.ligterink@icn.nl