ANOXIA - TREATMENT BY OXYGEN DEPRIVATION :
OPTIMIZING TREATMENT TIME OF MUSEUM OBJECTS
Michèle Gunn1*, Houri Ziaeepour2, Fabrice Merizzi3, Christiane Naffah4
1 Musee Quai Branly, 55 quai Branly, 75007 Paris, France.
2 Mullard Space Science Laboratory, University College London, Holmbury, St.
Mary, Dorking, RH5 6NT, Surrey, UK.
3Department of Islamic art, Louvre Museum, 34 quai Louvre 75001 Paris,
4 Centre de Recherche et de Restauration des Musées de France
14 Quai François Mitterrand 75001 Paris, France.
ANOXIA, treatment by oxygen deprivation is largely used for decontamination and
disinfestation of cellulose and protein-based organic materials. More specifically this method
is applied to more than one hundred thousand of objects destinated for a new museum in
Paris, "Musee du Quai Branly". We describe the anoxia installation in this museum and
report the result of a study regarding the efficiency of this method and the optimum treatment
time, crucial for treating a large collection. We show that the standard 21 days of exposure is
not always the optimal choice. Temperature plays a crucial role for hastening the death of
insects found within objects. At a temperature of 25°C, it is entirely possible to reduce
exposure times to 10 or 15 days for the insect species commonly found in museums. The
oxygen drop times is between 1 and 2 days for most objects, depending on type and porosity
of materials. This corresponds to a treatment time between 15 and 16 days. The effect of
humidity is less clear. It can increase the necessary treatment time both for larvae and for
Correspondence should be addressed to M.G. (firstname.lastname@example.org)
A large part of the collection of the future Musée du quai Branly - currently under
construction near the Eiffel Tower in Paris - is composed of cellulose and protein-based
organic materials. Such materials are favourable media for the development of micro-
organisms and insects, leading to their degradation.
This collection is presently being treated in a series of steps which include cleaning,
the taking of photographs, packaging and biological decontamination in the Le Berlier
building which has been especially equipped for this purpose.
The collection of the Musée du quai Branly, numbering about 275000 objects1,
comprises on the one hand collections from the Musée National des Arts d’Afrique et
d’Océanie (MNAAO) and the Musée de l’Homme (MH), and on the other hand has been
enriched by new acquisitions.
Studies of the general state of conservation of these collections in their original
institutions by experts, demonstrated the existence of infestation by Anobiidae, Dermestidae
and Tineidae, to name just a few. Infestation was found to be more or less serious depending
on the institution and departments in question. Given that it is difficult to reconstruct an
accurate case history of the infestation and the steps that have been taken to counter it, it was
decided to proceed with treatment of all objects containing organic materials, without
This prudent choice was made in view of the fact that the treated objects were not
destined to return to the site from which they came, but were going to be housed in a new
museum: a « complete overhaul » of the objets in order to reduce the level infestation to zero
is advisable under such circumstances. Furthermore, the objects are treated by oxygen
deprivation (anoxia), which minimises the risk of chemical degradation, althought some
discolorations of some pigments have been reported (TOSHICO, K., 1980); this cannot be said of
classical fumigation treatments even though the treatment times are much shorter in the latter
Heritage institutions currently employ oxygen deprivation treatment times (Tt) of 21 days.
This duration appears to have been adopted in the light of the results of experiments carried
out on a particularly resistant species, the rice weevil, an important pest in the food
industry : 500 hours (21 days) at 26°C, 12% relative humidity, in a nitrogen atmosphere
containing 1% oxygen. The exposure time is extended to 1000 hours (6 weeks) if the
temperature is lowered to 20°C (SELWITZ, C. et al, 1998).
Of more relevance in the museum field, the old house borer, Hylotrupes bajulus, is also a
species resistant to treatment by oxygen deprivation. Its favourite medium is resinous wood.
Eradication of this insect necessitated 20 days in somewhat different conditions: 20°C and
40% relative humidity. The duration can be reduced to 10 days if the temperature is raised to
30°C (VALENTIN, N., 1993).
It has gradually become standard practice to use a treatment time of 21 days. The
recommended conditions are in general as follows: less than 0.1% oxygen, a temperature
above 20°C and relative humidity of 50%.
The exact number will be established at the end of the collection treatment programme
There are a very large number of objects to be treated (more than 80% of the collection).
The deadline for completion of the collection treatment programme leads to constraints, in
view of which time is of the essence. It is therefore appropriate to analyse the time given to
each stage of the object treatment process in order that none be wasted.
If a reduction in the duration of oxygen deprivation treatment turns out to be possible, this
would enable a good speed to be maintained during the progress of the collection treatment
Consequently the key conclusion awaited from this study is the answer to the following
question: is the anoxia treatment efficient for an exposure time less than 21 days ?
Each anoxic treatment installation has its own characteristics. Thus, since the installation
we have used, named EPMQB (named according the name of the musée, Etablissement
Public Musée du quai Branly2), was specially designed for the Musée du quai Branly
treatment site, and was of a new and as yet untried form in the field of heritage and
conservation, it was necessary to carry out a study in order to optimize the conditions of
treatment for objects, in particular as regards oxygen drop times and exposure times.
The feasibility of treating infested museum objects by oxygen deprivation, either through
the use of oxygen scavengers, or in a controlled atmosphere of an inert gas such as nitrogen
(N2) or argon (Ar)) or carbon dioxide (CO2) is now well established. Resistant species such as
H. bajulus or A. punctatum (cellulose) can be totally eradicated, and this is also possible in
the case where insects are at the egg or larval stage which renders them more resistant to
treatment (Rust, M. et al, 1996 ; Selwitz, C. ; Maekawa, S., 1998). Many studies have already
been carried out by teams in the USA (Getty Conservation Institute) and Australia
(Australian Museum) for exemple. These studies have enabled the evaluation of influence of
different parameters, such as the level of oxygen (O2), temperature and relative humidity, on
the exposure times needed to achieve 100% mortality whatever the life cycle stage of the
Therefore, the goal of the study is to determine the efficiency of the EPMQB equipment
and the effectiveness of the traitement in the case of insects buried deep within an object.
This phase of the study should enable the degree to which oxygen is removed from the inside
of treated objects to be evaluated.
We report and discuss results obtained in the following areas :
1) the exposure time, Te, in the new EPMQB installation, leading to 100% mortality
irrespective of life cycle stage of the insects present in infested objects. The treatment
conditions are based on previous literature reports. They must be optimized from a mortality
viewpoint whilst avoiding endangering at the same time the physical structure of the treated
objects: an atmosphere with highly reduced oxygen content is used, between 1000vpm and
30vpm, a temperature of 25°C± 1°C and hygrometry of 50%± 5%.
2) the oxygen drop time, Ti33, defined as being the time taken to lower the oxygen
content in the treatment unit to the required level (0.1 %), and to study the effect of the
degree of loading with museum objects.
3) the oxygen desorption time of the objects Td. The Td value depends intrinsically on
the nature of the materials and the volume of the objects to be treated and the volume of the
Public Institution Musée du quai Branly
Ti, i for inert
anoxia chamber. The Td varies as a function of the permeability of the materials to gases, i.e.
nitrogen and oxygen in this case.
A - PROGRESS IN OXYGEN DEPRIVATION TREATMENT: MAIN RESULTS
OBTAINED BY OTHER INSTITUTIONS
I-TESTS ON INSECTS: EXPOSURE TIMES AND CLIMATIC CONDITIONS OF
The experiments carried out cover a very wide range of insects at all life cycle stages, i.e.
eggs, larvae, nymphs and adult insects. Atmospheres were modified through the use of the
three most frequently used gases: carbon dioxide (CO2), nitrogen (N2) and argon (Ar). The
anoxia treatment was performed in bubble chambers (VALENTIN, N.,1994; RUST, K. et al., 1996).
In some cases in order to simulate their being buried, insects were prepared in glass tubes
closed by a system allowing gaseous exchange. The tubes were subsequently left fixed within
blocks of wood. Other experiments were with sections of pine wood and with books of
dimensions which were artificially infested with the insects to be studied. The main results
show that :
- the most resistant life cycle stages of insects are eggs and larvae;
- not all the insects react in the same way, the old house borer is the most resistant;
- the treatment is more effective with argon than with nitrogen;
- temperature is an important factor whatever the other conditions.
The exposure time is reduced when the temperature increases; for example in the case of
H. bajulus (old house borer), when the temperature increases from 20°C to 40°C, the
exposure time is reduced from 21 days to 2 days. The studies carried out in the museum
environment show exposure times much lower than the standard of 21 days when the
climatic conditions are chosen appropriately, including for the most resistant species; for
- for the Anobiidae
or 5 days with 50% relative humidity, 30°C et 0.03% oxygen. One exception to this
range has been reported; this is Lasioderma serricorne (cigarette beetle), which
required 8 days at 25°C with 50 % relative humidity, or 9 days at 20°C and 40 %
relative humidity. (VALENTIN, N., 1993);
(e.g. : furniture beetle), complete elimination was achieved after 3
- for Hylotrupes bajulus (old house borer) of the Cerambycidae family, which has
shown itself to be rather more resistant, the exposure time was 10 days at 30°C with
40 % relative humidity or 20 days at 20 °C. (VALENTIN, N., 1993);
-for the Tineidae (e.g. clothes moths), 4 days at 25.5°C, 55% relative humidity and an
oxygen level below 0.1 % have been reported (RUST et al, 1996).
More recently in 2000, a Japanese team proposed a practical protocol for anoxia treatment
according to the type of insect. They advise 25°C or 30°C for one to three weeks. When the
temperature is 20°C exposure time should be extended to 10 weeks with an oxygen level of
0.2%. In evidence, in this case the high level of the oxygen makes the treatment time longer
than in the previous experiments (KIGAWA, R. et al, 2000).
The experimental parameters for treatment, according to the infestation, are actually
well known. The key questions which now remain to be answered are whether or not the
experimental conditions are really achieved within the treated objects.
II-DEMONSTRATION OF OXYGEN DESORPTION OF TREATED OBJECTS
The results outlined above were obtained by simulating the burial of insects within
objects in order to mimic as closely as possible a real situation. However, it is difficult from a
technical point of view to directly evaluate the desorption time Td of oxygen from objects,
since to do this would in principle necessitate the positioning of detectors within the objects.
Td depends on the porosity of the objects studied, and on the permeability of the materials to
the gas used. The duration of treatment therefore depends on the desorption time. Various
methods were used to evaluate desorption such as calculation of the time needed for the
oxygen level to reach its equilibrium value, and comparison of the treatment times of infested
objects with the treatment times of reference samples.
II-1 calculation of the time needed for equilibrium to be reached.
Simulation was carried out with fresh, non-infested wood from different sources: poplar,
oak, walnut, having fixed dimensions. The wood samples were bare or covered by a thick
protective coat. They were enclosed in a pocket of volume 32 litres (0.032m3) until
equilibrium was reached. The initial experimental conditions were:
23°C, 0.1% to 0.2% oxygen. Equilibrium was reached with 0.4% oxygen. Oxygen desorption
was found to be more difficult with painted wood than bare wood. The difficulty increase in
the way poplar, oak, walnut, with a maximum desorption time of 120 hours (5 days).
The same experimentrepeated for infested walnut wood showed a shorter desorption time:
equilibrium was reached more quickly, in one hour for the bare wood and in 4 hours for the
painted wood. This result is a consequence of the greater porosity of infested wood in
comparison to healthy wood on account of the tunnels hollowed out by the infesting insects
(SELWITZ, C., 1998).
II-2 Comparison of treatment time of infested objects with treatment time of reference
samples (test samples)
Treatments carried out on museum objects using readily available test samples as
references and performed in a controlled argon atmosphere showed similar exposure times
for the objects and the reference samples, the differences in exposure times being one day or
This result was not always observed. Wooden objects (pianos, sculpture and panels of
wood) infested by Anobium punctatum (furniture beetle) had to be treated over 10 to 14 days,
compared to only 4 for the reference samples. Similarly, 7 days were needed for a textile
sample of dimensions 135x87x43cm infested by Attagenus megatoma (black carpet beetle) as
compared to 2 days for the corresponding reference sample. The treatment conditions were as