Old Sturbridge Village

Old Sturbridge Village was the first of these institutions to act. The nature and size of its holdings create a substantial need for dealing with insect infestations. Webbing clothes moths and carpet beetles are the most common problems. In contrast to almost everyone else who is using carbon dioxide fumigation in a plastic bubble, Old Sturbridge Village carries out its treatments in a rigid metal chamber originally purchased in the early 1980s for operation with ethylene oxide. In 1989, with a few modest changes in the external plumbing, it was converted to use with carbon dioxide. The chamber, with a 2 m 3 capacity, can handle relatively small loads, but the conservators at Old Sturbridge Village have been able to turn to their colleagues at SPNEA for help with larger objects, such as sofas. The rigid chamber makes it possible to draw a slight vacuum, which speeds the purging process when a new run is started. The chamber is filled with carbon dioxide by two displacements. Instead of humidifying the gas stream, objects are conditioned to 45% RH before being put into the chamber. An infrared safety monitor outside the unit trips an alarm if the outside carbon dioxide concentration reaches 1000 ppm.

An efficient heating-evaporation device, placed between the gas cylinder and the chamber, is an important part of any carbon dioxide fumigation system. The carbon dioxide coming from the cylinder must evaporate and expand rapidly; in so doing, its temperature drops sharply. To avoid ice formation and other problems and to bring the carbon dioxide stream into the chamber at close to the desired run temperature, heat must be supplied at the point where the evaporation occurs. To do this, the Sturbridge system uses an in-line electric heater, E99-E-Heater 320, which is supplied by the Air Products and Chemicals Company. It is thermostatically controlled to operate between 24 and 29 °C (75 and 85 °F).

The W interthur M useum

In 1988 Rentokil representatives brought a small plastic chamber to the Winterthur Museum and successfully demonstrated the ability of carbon dioxide fumigation to rid trial objects of living insects. As a result, a standard 30 m 3 Rentokil bubble was purchased and installed in 1990 in an isolated area of the museum that had previously been dedicated to the use of toxic fumigants. Winterthur adopted a procedure that requires 14 days of treatment with 60-70% carbon dioxide at ambient temperature,, which is normally 20-25 °C. The carbon dioxide is not humidified. Although this has been a concern, result- ing in close inspections of treated objects, no damage due to not adding water vapor has been found. Rugs and upholstered furniture have been the most routinely treated items. Fumigations have been done primarily as a precaution rather than as a response to observed infestations. Objects, as they are received or sent out, are routinely examined for the possibility of infestation and the need

for processing. After several years of operation, the bubble has been needed less frequently and treatment schedules have been erratic. The unit was not used at all in 1995.

Society for the Preservation of New England Antiquities

In 1991 SPNEA had a burgeoning infestation problem. One of the historic houses under its management had become infested with webbing clothes moths. In addition, the house accidentally received an internal covering of soot from a malfunctioning furnace. Cleaning away the soot, exposure to a cold New England winter, and some contact spraying with insecticide eliminated about

95% of the infestation. However, rolls of textiles in the society's storage facility were also infested, and a standard Rentokil bubble was purchased and

Fumigation with Carbon Dioxide Fumigation with Carbon Dioxide

Only two weeks of treatment are required to eradicate powderpost beetles and clothes moths in textiles, even when these are wrapped in plastic film. However, on three occasions adult carpet beetles survived two weeks of fumigation, and the standard run time is now three weeks when this species is found. Very heavily infested objects may be subjected to two treatments. Longer run times and repeated treatments might have been avoided by operating the system at 25-30 °C. About four to six T-cylinders of gas are used per run. The carbon dioxide goes through a system of two gauges and a heat exchanger, which was obtained from the gas supplier. The carbon dioxide concentration in the room outside the bubble is monitored by an infrared analyzer, which is set to trigger an alarm and turn on a powerful ventilation system when safe levels are exceeded. The ventilation system is also used to exhaust carbon dioxide from the bubble and draw in air at the end of a run. Over a four-year period leading into 1996, thirty-five treatments, averaging about one hundred objects each, had been put through the three-week process without any apparent failure. SPNEA also does work for other institutions. Perhaps the most unusual assign- ment was the treatment of bales of hay used to make a sculpture for display in the Portland Museum, in Maine.

Old Sturbridge Village