Rigid Chambers Homemade Containers

While a number of institutions carry out treatments in rigid and substantial plastic or metal containers, there are no units commercially available in the sense of

being listed specifically for nitrogen anoxia. However, there are many commercial chambers or containers for other uses that could readily be adapted for anoxia. Museum personnel, with considerable skill and ingenuity, have built anoxia chambers out of pipes, boxes, water tanks, and units designed for use with toxic pesticides. Chambers formed from a single molded piece of plastic and an easily attached cover have generally worked well, while boxes assembled from flat panels and joined by gasketed rims have not. Koestler (1992) even built

a treatment system out of a heavy-gauge polyethylene utility storage cart. A

Chapter 7

Figure 7.5

Diagram of custom-made anoxia chamber used by Alan Johnston. (Courtesy of Alan Johnston.)

Side elevation

End elevation

Plan of chamber rim

Plexiglas cover was sealed to a polyethylene chamber with silicone adhesive to create a container with an oxygen leak rate of only 50 ppm per day, which could

be brought to an initial oxygen concentration of 50 ppm. Unfortunately, a new seal had to be prepared for each application.

Alan Johnston, of the Hampshire County Council Museum Service in the United Kingdom, put together a similar container (Fig. 7.5) using inexpensive off-the-

shelf materials. It consisted primarily of a commercial polypropylene water tank, measuring 1 × 0.5 × 1 m, and an oval lid cut from a 10 mm thick sheet of cast polycarbonate. Johnston (1996) was able to solve the sealing problem with ordi- nary woodworking C-clamps, a large neoprene O-ring designed for aircraft

doors, and a smooth rim on the water tank. Nitrogen, humidified by passage through a three-bottle bubbler system, is fed into the chamber through a one- way truck tire valve set into the polycarbonate lid. This is connected to perfo-

rated rubber tubing that coils around the base of the tank and distributes the nitrogen. The gas leaves the chamber through a simple valve system either

directly to the atmosphere or through a Teledyne oxygen monitor. The valve arrangement allows either evacuation or purging. Although the system can be

brought to an oxygen concentration of 200 ppm when the unit is closed tightly, oxygen levels will climb to 1% over 168 hours. The system is most conveniently operated with the exit valves slightly open to allow a small flow of nitrogen to move through the tank. RH and temperature readings are made using a Meaco

radio telemetric sensor within the chamber that transmits data to a central envi- ronmental monitoring computer. RH is also followed in the third mixing jar of

the bubbler system with a simple digital Meaco meter. Steven Pine, of the Museum of Fine Arts in Houston, has also designed and con-

structed several different types of rigid chambers for special applications. He converted a 20 ft (6.1 m) length of standard 15 in. (38 cm) diameter PVC pipe into a treatment chamber for long and awkward objects like spears and rolls of fabric (Fig. 7.6). Building this unit required a section of SDR 35 PVC gasketed sewer pipe, two 15 in. (38.1 cm) PVC caps, two 0.5 in. (1.27 cm) diameter

Reusable Anoxia Systems

Figure 7.6

Anoxia chamber made of PVC sewer pipe. (Photo courtesy of Steven Pine, The Museum of Fine Arts, Houston.)

silicone O-rings, and eight latches. First, the flange end of the pipe was cut off, then each PVC cap was cut perpendicular to the axis to provide both a collar and

a half cap. Collars were mounted at each end of the pipe with PVC cement, and the half caps were attached with latches and made gastight to the collars with the O-ring gaskets. Humidified nitrogen is brought in at one end of the pipe through a cap and out the other end through the second cap, either directly to the outside or through an oxygen monitor (Fig. 7.7).

Figure 7.7

Diagram of improved PVC prototype. (Courtesy of Steven Pine, The Museum of Fine Arts, Houston.)

Usual humidification system

A cap cut in half yields a half cap and a collar, which is welded onto the pipe with PVC cement.

Digital hygrometer placed in third jar allows for RH reading of the N 2 entering the tube.

Large end of pipe is cut off.

Humidified N 2

Half cap

Four latches on each cap

O 2 monitor

T-valve N 2 outlet Input

O-ring gasket made of silicone Materials

(1) 15 in. × 20 ft (38 cm × 6.1 m) SDR35 PVC gasketed sewer pipe (2) 15 in. (38 cm) PVC gasketed sewer caps (two)

(3) 0.5 in. (12 mm) silicone gasket O-rings (two) (4) Teledyne oxygen monitor

Chapter 7

Any tightly sealable container with substantial walls that allow the installation of gas and utility lines should be convertible to an effective anoxia chamber. Hardigg Industries makes such reusable containers in a range of sizes, and Pine

3 has converted a 9 ft 3 (0.3 m ) case, shown in Figure 7.8 with gas ports and sensor connections, into a compact system with nitrogen supply and humidification

(Fig. 7.9). This is easy to build and effective for the disinfestation of small objects in a standard dynamic process of allowing nitrogen to flow through the container for 5-20 days as needed, after the oxygen content has been lowered

below 1000 ppm.

Rigid Chambers Homemade Containers