Environmental and health concerns have caused a radical change in the popular perception of chemical pest control methods. Governmental and environmental agencies seek to further limit the uses of chemicals in areas that have, till now, accepted them as routine treatments. As an example, the German Dangerous Substances Act requires that "toxic gases may no longer be employed if a toxin free procedure is effective and reasonable." Here in the UK, if we are to be realistic, we must also anticipate a general move in this direction. These concerns have led to the development of what are essentially two new processes. Designed to treat insect pests in objects these treatments are thermal with controlled humidity and inert gas fumigation.
The treatment and restoration of rare and valuable objects, in a sensitive and non invasive way, is a priority for anyone concerned with conservation. Insect pests account for much loss and damage every year and are partly responsible for the slow erosion of our cultural heritage [ Pinniger 1994]. Buildings of architectural value are equally affected both in the country and in the urban environment. In the field of building preservation a hot air method has been applied successfully for several decades. Using high pressure heated air the temperature of roof timbers and building frames can be raised to over 55°C. At such temperatures animal protein within the insect cell becomes irreversibly denatured resulting in death [Strang, 1992]. The main problem encountered in applying this sound biological principle to the treatment of high value works of art, antiques etc. has been the resultant dehydration of the piece. This has caused shrinkage and cracking and leads to irreversible damage.
The eradication of insect pests in such a sensitive area requires a method which includes precise control over all the environmental parameters. This is especially true of the relative humidity. Methods & Materials
The development task was to find a treatment which could:
The thermal solution is the technically refined version of the previously discussed heat treatment. A chamber was designed in which infested objects could be placed and the environment modified precisely by computer. In both the warming up and cooling down phases of the treatment the relative humidity is controlled in such a way as to ensure that the humidity balance is maintained. As a result no dehydration can occur. The patented Thermo Lignum process is currently being used commercially to treat a variety of organic materials such as furniture, textiles, herbaria, books, manuscripts, silks and leathers. It is suitable for antiques and museum exhibits [Pinniger 1995] and being used in the treatment of in-situ timbers such as roof trusses and timbered buildings.
This technology provides a totally object-focussed and flexible method of pest eradication. Completely new systems were developed to make this concept workable in practice. Suitable measuring and control technologies were selected as well as an intelligent system management unit to control these complex physical, climatological and technical processes in an integrated and largely labour-free way.
Thermal pest treatment with humidity-controlled warm air is currently applied in climatic chambers. It is fast, safe and economically sound. Because of the careful design of the application technology it is now possible to adapt this method to the individual conditions and requirements [Child 1994] of both the restorer/conservator and the object to be treated. It can be used for in-situ applications both in rooms and now for entire buildings.
Further development and feedback has suggested other, more widespread, applications for this process and research continues.
Child, R.E.  The Thermo Lignum process for insect pest control. Paper Conservation News 72 
Piening, Heinrich  Modified inert atmospheres in pest control or when in doubt let the object decide. Paper presented during Symposium on Workplace Medicine, Dortmund 1995.
Pinniger, D.B.  Insect pests in museums. 3rd Ed, Archetype Press London.
Pinniger, D.B.  Insect control with the Thermo Lignum treatment. Conservation News March 1996.
Strang, T.J.K.  A review of published temperatures for the control of pest insects in museums. Collection Forum 8 
Strang, TJK  The effect of thermal methods of pest control on museum collections. Proceedings of the 3rd International Conference on Biodeterioration of Cultural Property, Bangkok, Thailand 1995