Vacufume Chambers

Conversion of commercial metal fumigation chambers originally designed for use with gaseous pesticides can provide a unit in which anoxia with high-purity nitrogen is effectively carried out. An example of this is the Vacufume Fumigator-36, which was manufactured by the Vacudyne Company. Several thousand have been sold, mostly to hospitals for sterilization treatments, but a few were acquired by cultural institutions like the Los Angeles County Museum of Art (LACMA) and the Royal Ontario Museum in Toronto. Conversion of this chamber for anoxia treatments consists primarily of installing a humidification system and providing gastight entry to the box for humidity and oxygen moni-

Figure 7.8

toring cables. Vacudyne offers conversion kits, and a number of museums have

Hardigg case with taps. (Photo courtesy of

made the change. LACMA purchased a Vacufume chamber in 1983 for use with

Steven Pine, The Museum of Fine Arts,

ethylene oxide at about the time that this fumigant fell out of favor. Conse-

Houston.)

quently, the unit was never used with ethylene oxide. Researchers at the Getty Conservation Institute proposed that the Vacufume chamber be converted to operate by anoxia. Shin Maekawa and Vinod Daniel of the GCI, along with Steve Colton of LACMA, designed and made the necessary modifications. The

Vacufume Fumigator-36 is a large metal box with an inner capacity of about

1.02 m 3 . It measures 0.91 m square at the base and is 1.22 m high. The large gasketed door is sealed with four wheel latches, one at each corner, and when

tightly closed, the chamber has an oxygen leak rate of about 200 ppm per day. The ability to keep oxygen inflow to this level is a major reason that the Vacu- fume unit is an attractive candidate for conversion.

Figure 7.9

Anoxia system based on Hardigg case. (Photo courtesy of Steven Pine, The Museum of Fine Arts, Houston.)

Reusable Anoxia Systems

Infestations in the LACMA collection are not common, but the chamber finds frequent use treating new acquisitions and incoming pieces on loan with no fumigation history. In a typical treatment carried out in April 1996, the chamber was loaded with a large, well-wrapped, papier-mache construction held in a cardboard box and a small painting in a wooden frame that showed signs of infestation. After the door was closed, the latches were secured tightly, and a vacuum of 5 psig was pulled. The purpose of the vacuum is to remove some oxygen, to determine if the seal is holding, and to ensure that the chamber is made as gastight as possible. The reading on the oxygen monitor fell to 17.5%. This showed that there was a good seal and that it was possible to turn and tighten the latches just a bit more. The humidification system, consisting of three stout, half-gallon, polypropylene bottles, was attached to the left outside wall of the chamber as shown in Figure 4.1. Humidification is provided and measured as described in chapter 4. Nitrogen first sweeps out the air in the bubbler system via the purge line just before the entry valve to the chamber. Then the nitrogen is sent into the chamber, bringing it up to atmospheric pressure. A vent from the chamber is then opened to allow the unit to be flushed with nitrogen to achieve the required level of oxygen. In a typical run, the RH in the humidification system would quickly rise to 65%. This is higher than the RH in the chamber because the pressure there is higher. After the gas streams in the bubbler system were adjusted to send less nitrogen through the water bottle, the RH in the third bottle fell to 57%, and the RH in the chamber leveled at about 50%. The chamber is typically operated with the RH at 45-55%. Flushing the system over three eight-hour shifts with 99.995% nitrogen brought the oxygen concentration to 600-800 ppm. The chamber allows 200 ppm oxygen to leak in over twenty-four hours, so sealing it at this level means that the oxygen level will drift up to under 3000 ppm, or 0.3 %, over ten days. This is within the allowable increase in oxygen concentration for an effective anoxia treatment.

The Vacudyne Company has been testing a prototype of another kind of rigid- chamber anoxia system, offering the possibility that a turnkey unit will be made available commercially. The system uses a conventional 50 gallon (190 liter) steel drum for the anoxia chamber and comes with a three-jar humidification system as well as the necessary gas and utility lines. The unit has been evaluated by Mark Roosa, chief preservation officer for the Huntington Library Art Collections and Botanical Gardens in San Marino, California. The system will purge down to an oxygen concentration of 2000 ppm in 6-8 hours using nitrogen containing

20 ppm oxygen. Treatment is generally run at 2000 ppm oxygen, 20 °C, and 45-50% RH for up to 7 days, depending on the nature of the infestation. At the Huntington Library, treatment is done only where infestation is seen or highly suspected. Pests have included silverfish, lice, beetles, and termites, which have attacked books, masks, papier-mache objects, photographs, and other archival material. This is a usable and relatively inexpensive system that can be trans- ported to sites as needed. The main limitation may be one of capacity.

Chapter 7

Chapter 8

Although cultural institutions use anoxia more widely than they do carbon dioxide fumigation to control infestations, the quantity of material treated by carbon

Fumigation with dioxide fumigation is larger. When big reusable chambers are employed to treat

large batches of material, carbon dioxide is the gas of choice because gas com-

Carbon Dioxide positions effective for killing insects are more readily and cheaply achieved with

it than with nitrogen. It is faster and easier to replace 60-80% of the air in a

30 m 3 bubble with carbon dioxide than it is to purge the chamber to an oxygen content of 500 ppm with high-purity nitrogen and hold it at that level. Carbon

dioxide is preferred over nitrogen because it requires less stringent sealing conditions and because fluctuations in concentration have much less influence on per- formance. Carbon dioxide is not used with pouches and small containers, where argon and nitrogen work well. Many institutions use both carbon dioxide fumigation in large reusable bubbles and nitrogen treatments in bags to deal with infestations. Other reasons for favoring carbon dioxide for large-volume opera- tions are its much lower cost than nitrogen on an equal volume basis and the lesser need for auxiliary humidification. A nitrogen purge sweeps out all ambient moisture from a treatment container, but at a 60% carbon dioxide level, 40% of the original water vapor remains. In addition, large chambers are often filled with objects in wooden and cardboard boxes packed with paper, which provides

a considerable amount of moisture buffering. There is some concern about the formation of carbonic acid when carbon dioxide encounters water during treatment as pointed out by Reichmuth (1987). The carbonic acid provides a pH of 4, which might damage sensitive materials such as metal filaments, zinc objects, and organic pigments. These could be harmed by the acidity, and conservators should be aware of this factor when planning treatment. However, no problems of this type were noted in the many reports on carbon dioxide fumigation reviewed for this chapter.

Effectiveness of Carbon Dioxide versus Nitrogen

To the extent that a direct experimental comparison can be made, nitrogen containing very low concentrations of oxygen appears to be the more lethal medium. In a study comparing nitrogen, argon, and carbon dioxide, Valentín (1993) observed that there was very little mortality among Hylotrupes bajulus,

especially old larvae and pupae, held in an atmosphere of 60% carbon dioxide at

30 °C for 3 weeks. Under the same conditions with nitrogen containing 300 ppm oxygen, total mortality of all life stages of the borer is achieved in 10 days. Valentín found that for most beetle pests found in museums, exposure to 60% carbon dioxide for 10-25 days at 30-35 °C was needed, while nitrogen contain-

ing 300 ppm oxygen required only 4-6 days. She concluded that when comparing nitrogen or argon with carbon dioxide under typical fumigation conditions,

the carbon dioxide atmosphere was ineffective for controlling populations of Cerambycidae (boring beetles), and elimination of species in the Anobiidae and Lyctidae families took more time than with nitrogen. Banks and Annis (1990)

attempted to make a comparison based on the limited available literature and concluded that none of the gases has a marked advantage. However, the two studies they cited (Jay 1984; Reichmuth 1987) both describe the use of nitrogen containing 10,000 ppm (1%) oxygen, which is essentially ineffective for anoxia. Therefore, conclusions that nitrogen is no more effective than carbon dioxide were erroneously based on studies made with high oxygen concentrations.

Vacufume Chambers