The Sector That Cannot Spray: Collection Pest Management and What It Knows

1. Introduction: a sector with every constraint

This journal has argued repeatedly that pest control is limited by what a client will pay and what a label permits. Here is a sector limited by more than either.

1.1 Two sentences containing the whole argument for physical control

The chemicals did not solve the problem and are still there.¹

1.1b And the sector is closer to ours than it looks

Its problems are our problems in a smaller box: the same insects, the same materials they feed on, the same question of whether a treatment reached the place the animal actually is.

1.2 What this article argues

That a sector forbidden the usual tools produced better-specified protocols than the sector that has them, and that its two central technical warnings are ones structural work keeps rediscovering. Sections 9, 14 and 17 are the case.

2. What the constraints are

Our summary, since no single source lists them.

A residue cannot be left on an object that is itself the thing being preserved. An infested item cannot be discarded, because keeping it is the entire purpose. And there is no threshold below which damage is acceptable, because the object is not replaceable.

2.0b And the objects are also the food

Keratin in furs and feathers, cellulose in paper, starch in bindings and adhesives: a collection is assembled from exactly the materials our clothes moth and carpet beetle article identified as the larval diet.

That observation is ours and it explains why the problem is chronic rather than occasional.

2.0c And there is no option of moving the asset

A warehouse can relocate stock and a household can discard a mattress. Neither move exists here.

2.1 Which inverts the logic our threshold article described

An economic injury level presumes a value that can be compared against a control cost. Where the item cannot be replaced at any price, the comparison has no second term.

2.1b And the damage is cumulative rather than episodic

A crop is harvested and a building is repaired. A collection accumulates every loss it has ever had, so the standard is not annual damage but total damage over an indefinite period.

2.2 And the people are a constraint too

Conservators handle the objects continuously, so a treatment safe for the material but not for the handler is not available either.¹

3. So what is left

Physics.

The two most common procedures at the specimen or collection level are low-temperature freezing and low oxygen anoxia treatments, with the most common physical treatments using temperature extremes, heat above about forty degrees and cold below about ten, alongside controlled or modified atmospheres.¹³

3.0b Both also leave nothing behind

Which is the property that made them acceptable, since the objection in §1 was to residue as much as to toxicity.¹

3.1 And both work on the whole organism at once

Neither method has a target site, a mode of action or a class. An insect denied oxygen or held below its lethal temperature has nothing to be resistant with, which is why our resistance articles have no counterpart to this section.

3.2 With one qualification from §17

Cold tolerance varies and can be conditioned, so physical treatment is not free of biological variation even if it is free of resistance.⁶

4. Where the methods came from

Not from conservation.

Atmospheres with low concentrations of oxygen had been used for the control of pests in stored food products for several decades before this method was adapted to the treatment of museum artifacts in the late 1980s, with considerable research on modified atmospheres in stored food conducted since about 1970.⁷

4.1 Which is unusual for a conservation method

Most preventive conservation practice was developed inside the field for its own materials. This one arrived from an industry whose concern was the price of wheat.

5. Which is a lineage worth noticing

Our observation.

Grain storage developed controlled atmosphere treatment because it had sealed structures, a tolerance for long exposures and a reason to avoid residues in food. Museums inherited it because they had the same three properties.

5.0b And the transfer was of a method rather than a product

Nothing was registered, nothing was formulated and nothing was sold. An approach developed for grain was read, adapted and tested against a different set of species, which is a route into practice that this journal has rarely seen.

5.0c And the receiving sector had a reason to look

A field already worried about what its old chemistry had done to its objects was unusually motivated to find a method that leaves nothing, which is a precondition most sectors do not have.¹

5.1 Structural pest control has none of them

Buildings are not sealed, occupants will not wait three weeks, and the objection to residues has never been strong enough to force an alternative.

5.2 Which is why the method did not travel here

And our fumigation article described the one structural case where sealing is attempted, along with how difficult and expensive it is.

6. The oxygen protocol

The recommended protocol suggests an oxygen percentage below 1% for at least three weeks.²

6.1 Three weeks is the striking figure

Longer than any structural treatment this journal has described, and available only because the item being treated has nowhere else to be.²

7. How it was arrived at

Over three decades.

A 1991 report determined that atmospheres low in oxygen but rich in nitrogen, at 0.4 per cent oxygen, were effective in killing laboratory cultures of webbing clothes moths, cigarette beetles, drugstore beetles and a carpet beetle species.⁵ Work the same year proved the efficacy of nitrogen with less than 0.1% oxygen to kill all life stages of the ten commonly found museum insects studied.⁴

7.0b And the species list is the domestic one

Webbing clothes moth, cigarette beetle, drugstore beetle and a carpet beetle are the same insects our stored product and fabric pest articles cover, so a protocol built for collections was built against the pests of an ordinary cupboard.⁵

7.0c Ten species is also unusual

Most efficacy work this journal has examined tests one or two, and a protocol validated against ten can be applied to a mixed collection without knowing which insect is present.⁴

7.1 All life stages is the demanding phrase

Eggs and pupae are the stages that survive treatments aimed at adults, which our flea and cockroach articles both described as the reason a single application fails.⁴

8. And why it moved upward

For an operational reason.

Although it is possible to maintain a 0.1 per cent oxygen concentration, this may not be easily achievable in museums for large applications such as a large enclosure, so research was extended to higher oxygen concentrations.⁴

8.0b And the constraint is enclosure volume rather than chemistry

Holding a gas concentration gets harder as the sealed space gets larger, so the limit on the method is the same limit our fumigation article found: how well you can seal what you are treating.⁴

8.1 Which is the right direction to move a protocol

From what works in a laboratory toward what can be held in a room, with the efficacy question re-asked at each step rather than assumed.

That assessment is ours.

8.2 And the practical problems are named

The major practical problems of controlled atmospheres are connected to treatment time and low oxygen percentage, which is why more flexible protocols at higher oxygen or shorter times are sought.²

9. The factorial study

The extension evaluated the effect of relative humidity on mortality of two common museum insects at 33, 55 and 75 per cent relative humidity, in a nitrogen atmosphere with oxygen concentrations of 0.3, 0.6 and 1.0 per cent.⁴

9.1 The species chosen are informative

Two beetles, one a stored product pest and one a fabric pest, which are the two damage routes a mixed collection faces.⁴

10. Which is more design than we usually see

Our comparison.

Three oxygen levels crossed with three humidity levels against two species is nine conditions per species, which is a dose-response surface rather than a demonstration that a treatment works.

10.0b Nine conditions is not a large experiment

By the standards of agricultural trials it is modest. By the standards of the efficacy data our registration article examined, where a single exposure at one condition can satisfy a requirement, it is generous.

10.1 And the reason for it is stated

At oxygen percentages higher than those commonly used, temperature and relative humidity are very critical to insects' development and success.²

10.1b And the direction of the research is worth contrasting

This programme asked how far a working protocol could be relaxed before it stopped working. Most efficacy testing we have examined asks only whether a proposed treatment works at the condition proposed.⁴

10.2 Which is the same structure as our fumigation article's concentration and time product

Except with two more axes, because at the margins of a treatment the conditions surrounding it start to matter more than the treatment itself.

11. Gas choice matters

Which we had not expected.

A study of modified atmospheres against the larvae and adults of two named museum species determined lethal times for different exposure periods at twenty and thirty degrees, and argon atmosphere achieved higher mortality than nitrogen for both insect species.²

11.0b And the practical difference is cost

Nitrogen is cheap and can be generated on site. Argon is neither, which means a result favouring argon is a result that has to be worth paying for.

That is our reading and the source draws no such conclusion.²

11.0c And temperature moved the result as well

Mortality was generally higher at thirty degrees than at twenty, so the gas comparison sits inside a treatment where warmth is already doing part of the work.²

11.1 Both gases are inert

So a difference between them is a difference in how the insect responds rather than in chemistry acting on it, which is a result worth an explanation we do not have.

12. And the stage that matters is the tougher one

From the same work.

The adults were more sensitive than larvae, with mortality generally higher at elevated temperature.²

12.0b And it is the opposite of the usual assumption

Adults are the visible stage and the one most treatments are aimed at. Here they are also the easier one to kill, so a result that looks like success may leave the stage doing the damage untouched.²

12.1 Which is the wrong way round for a collection

Larvae do the feeding damage in both of the groups this journal has written about in a domestic context, so the resistant stage is also the destructive one.

12.1b And it is the reverse of the pattern for gases in grain

Where our phosphine article found eggs and pupae the tolerant stages. A result placing larvae above adults in tolerance is specific enough to matter and specific enough to want confirming.²

12.2 And it explains the length of the protocol

Three weeks is a duration set by the hardest stage rather than by the average.

Both are ours.

13. The cold protocol

Practical low temperature guidance falls in the range of roughly minus twenty to minus thirty degrees, with exposure periods commonly around one to two weeks depending on the protocol.⁶

13.1 Speed is why institutions choose it

One comparison notes that a common reason to consider freezing is speed, with published museum protocols often using about one to two weeks of low temperature exposure against three weeks for the gas method.⁶

13.1b Which is an unusually honest framing for a supplier page

Since the same source sells equipment for both, and declining to name a winner is not the commercially obvious move.⁶

13.2 And neither method is presented as generally better

The choice is described as depending on the object, the pest, treatment time, available equipment and the institution's workflow, with the decision meant to start from collection risk rather than from the equipment already owned.⁶

14. The warning inside it

The guidance stresses that treatment success depends on reaching the required temperature throughout the object, not just in the freezer air, and that if the centre remains warm the treatment may not be complete even though the freezer display shows the target temperature.⁶

14.1 It is phrased as a condition of success

Depends on, rather than should ideally include, which is the difference between a requirement and a recommendation.⁶

15. Which this journal has made about heat

In the other direction.

Our articles on whole-room heat treatment found the same problem: air temperature reaches target long before the interior of a mattress, a wall void or a piece of furniture, and the insects are in the interior.

15.0b And the failure mode is the same too

A treatment that reads as complete and is not, with the operator having no indication that anything went wrong until the insects reappear.

15.1 The physics is identical and the sign is reversed

An object has thermal mass, thermal mass resists change, and the measurement that matters is the one you cannot easily take.

15.2 The difference is that this sector says so in its guidance

Prominently, as a condition of the treatment rather than as a caveat.⁶

16. Do not trust the display

Stated as a recommendation.

It is recommended that performance be monitored with a separate thermometer, along with ensuring the freezer is well insulated and providing adequate air circulation inside it around the objects.⁸

16.0b And the loading of the chamber is part of the treatment

Air circulation around objects determines how fast each one cools, so packing a freezer tightly changes the exposure every item receives.⁸

16.0c And the equipment recommended is ordinary

A commercial hardening freezer is a food industry product, not a conservation instrument, which puts the method within reach of institutions with no specialist budget.⁸

16.1 Three requirements, none of them about the insect

Independent measurement, insulation and air movement are all properties of the equipment and its loading.

17. The variable that should unsettle anybody

Listed among the things affecting outcome.

Species, life stage and previous temperature history can affect cold tolerance.⁶

17.1 It sits in a list of three

Alongside species and life stage, which are fixed properties of the animal. Previous temperature history is a property of what happened to it beforehand.⁶

18. Which our bed bug article measured

And found in numbers.

That article reported rapid cold hardening: an hour at zero degrees improved survival at much lower temperatures afterwards, an asymmetry in which the insect could prepare for cold but not for heat.

18.0b And the object's own thermal mass sets the cooling rate

Which means a large or dense item necessarily descends slowly through the moderate cold that §18 identifies as a conditioning range, whatever the freezer is set to.⁶

18.1 So an object cooled slowly may be harder to treat than one cooled fast

Because the descent through moderate cold is itself a conditioning exposure.

18.2 Which is a reason to want a colder freezer rather than a longer one

And may be part of why equipment operating at minus forty-two degrees appears in the guidance.⁸

Sections 18.1 and 18.2 are our inference, and neither source connects the two findings.

19. The handling details

Which are about the object rather than the insect.

Objects are normally enclosed in a suitable vapour barrier bag or equivalent container before freezing, and after treatment the sealed object is allowed to return to room temperature before the bag is opened.⁶

19.0b Which is a treatment step aimed entirely at the object

Nothing about bagging or slow warming affects the insects. Both exist to keep the treatment from damaging what it is protecting, which is a category of protocol step that structural work does not have.⁶

19.1 Condensation is the reason

Which we state from general knowledge rather than from the source, since a cold object exposed to warm air collects water.

20. Heat, and its limit

The third physical method.

Thermal treatment is limited to museum objects that contain thermally robust materials.⁷ One method developed at a national conservation institute uses sunlight to produce temperatures lethal to insects, and buildings and large installations can also be heated with hot air.⁸

20.0b And one method uses no equipment at all

Producing lethal temperatures from sunlight, which is a treatment whose entire cost is a bag and patience.⁸

20.1 Which is the constraint our heat treatment articles describe from the other side

Where the question was whether a building's contents would survive, rather than whether an object would.

21. What the chemical era left

The passage quoted in §1 is the sector's own account of what preceded the physical methods.¹

21.1 The sequence took the same shape as everywhere else

Heavy metals first, then fumigants, then a search for something that does not leave anything behind, which is the arc our own chemistry articles trace across agriculture and structural work.¹

22. The objects are the hazard now

Which is the part we find most striking.

Material applied to preserve a collection remains in that collection and must be known about by the people who handle it, decades later.¹

22.0b Which is a hazard with no expiry

Arsenic and mercury compounds do not degrade into something harmless, so a treatment applied a century ago is present in the same quantity today.

We state that from general chemistry rather than from any source here.

22.1 A bibliography entry makes the same point

Describing an article on the history of pest control techniques in one major collection as helping conservators understand that a variety of materials may have been used historically on the objects in their care, and supporting recommendations for improved documentation of treatments and health safety precautions for people working with collections.⁵

22.1b And the documentation recommendation follows from that

Improved documentation of treatments is recommended alongside health safety precautions, as a pair rather than as two separate good practices.⁵

22.2 So the record of treatment became a safety document

Which is an argument for documentation that no commercial pest control contract has ever had to make.

That observation is ours.

23. And it did not even work

Which is the other half of §1.

The heavy metal treatments and the later fumigants do not fully protect them from infestation.¹

23.0b And an open collection keeps receiving material

New acquisitions, loans returning and objects moving between institutions all arrive with whatever they carry, which is why quarantine of incoming material sits alongside treatment in every account we read.

That framing is ours.

23.0c Which is the strongest case for prevention in the whole article

If the most aggressive chemistry ever applied to these materials did not keep them clean, then nothing applied episodically will, and the cabinet and the humidity control are doing the work.¹

23.1 Because a treatment is an event and exposure is continuous

A fumigation kills what is present and leaves nothing against what arrives next, which is the distinction our residual chemistry articles turn on.

24. Prevention is the rest of the programme

And it is recognisably exclusion.

Recommendations include using inert materials for specimen storage, such as polyethylene foam rather than cotton wool, using well-sealed storage cabinets, keeping relative humidity low, and using micro-environments where collections must be stored in damp places.¹

24.0b With one item that has no structural equivalent

Choosing the storage material itself for whether it feeds anything, which a building owner cannot do about a building.¹

24.1 Which is our own advice at a smaller scale

Seal the container, remove the food material, control the humidity. A cabinet is a building and a specimen tray is a room.

24.2 And humidity control does double duty

Keeping relative humidity low addresses insects and the fungal problems that arrive with damp storage at the same time, which our own moisture articles found to be the general case.¹

25. What transfers to buildings

Three things, in our view.

Measure inside the thing you are treating. Sections 14 to 16.⁶

Treat prior thermal history as a variable. Section 17.⁶

And document what was applied, for the next people. Section 22.¹

25.0b And one that transfers to our own records

Keeping a treatment history that would still be useful to somebody in thirty years, which costs almost nothing and which §22 shows can matter enormously.

25.1 With one that transfers to a client conversation

That a treatment which cannot be verified at the point where it has to work is a treatment whose success is being assumed, which is a thing worth saying out loud before doing it.

26. And what does not

Most of the rest.

Three weeks in a sealed enclosure at controlled humidity is available for an object and not for a house. The methods are excellent because the constraints permitted them, not because anybody chose rigour over convenience.

26.0b And the treatment unit is the difference

Collections treat objects. Structural work treats spaces, and a space cannot be lifted into a chamber, which is the single fact that separates the two sets of options.

26.0c And their monitoring problem is easier too

A sealed chamber can be instrumented completely. A building cannot, which is why our detection articles keep arriving at probabilities rather than certainties.

26.1 Which tempers the whole argument

A sector that can put the problem in a bag has options a sector working in occupied buildings does not, and comparing the two on protocol quality alone would be unfair.

27. Our own position

The disclosure.

We do not work on collections and have no commercial interest here. An article praising another sector's rigour is also an article implying our own is weaker, and §26 is where we say why that comparison is not entirely fair to us.

27.1 And the comparison in §25 is the useful part

Not that conservators are more careful than pest control technicians, but that their constraints forced them to write down things this trade has been content to leave implicit.

28. The Manitoba position

28.1 The guidance we relied on is Canadian

The low temperature figures and the object core warning come from a national conservation institute's published advice, which is the domestic source in this article.⁶⁸

28.1b And the national institute is the relevant authority

A Canadian conservation body produced both the low temperature guidance and the solar heat method described in §20, which makes this one of the few areas where the domestic guidance is the one everybody cites.⁶⁸

28.2 What we could not find

Any account of collection pest management at institutions in this province, and any local record of what treatments were historically applied here.

28.2b Which does not make an outdoor winter a treatment

Ambient cold is uncontrolled, fluctuates, and descends slowly, which §18 says is the condition under which tolerance improves rather than fails.⁶

28.3 And the climate is relevant for once in a useful direction

A place with a long deep winter has ambient conditions closer to a treatment temperature than most places do, which we note as an observation rather than a recommendation.

29. Limitations and open questions

We read no primary study in full. The anoxia and cold tolerance results reach us through a review abstract, a bibliography entry, a newsletter article and institutional guidance, none of which is the work itself.²⁴⁵⁶

That is the most important limitation because §§7 to 12 report specific concentrations, species counts and comparative mortality from summaries, and a summary is a poor basis for a claim about what an experiment showed.

One key source is a trade page. The cold temperature range, the object core warning and the previous temperature history variable, which together carry §§13 to 18, come from a commercial supplier's article describing a conservation institute's guidance rather than from that guidance directly.⁶

The argon result has no mechanism. Section 11 reports a difference between two inert gases and we found no explanation for it.²

The dates are uneven. Some of this work is from the early 1990s and we did not establish what has superseded it, so a protocol described as current may have moved.⁴⁵

And the chemical legacy is one institution's statement. Section 21 rests on a single page, supported by a bibliography entry about one collection.¹⁵

Sections 2, 5, 10, 12, 15, 18.1, 18.2, 22.2, 24.1 and 26 are our reasoning. The account of the constraints, the lineage argument, the comparison with heat treatment practice, the connection to rapid cold hardening and the qualification in §26 are ours rather than sourced positions.

30. Conclusion

A sector that cannot leave a residue on the thing it is protecting, cannot discard what becomes infested, and has no threshold of acceptable damage, was left with physics. Its two main methods are low temperature and low oxygen, both adapted in the late 1980s from stored product protection, where modified atmosphere research had been running since about 1970.¹⁷ The oxygen protocol was built over three decades: nitrogen at 0.4 per cent oxygen killing four named species, then under 0.1 per cent killing all life stages of ten, then, because 0.1 per cent is hard to hold in a large enclosure, research upward through higher concentrations crossed against three relative humidity levels, landing at under one per cent for at least three weeks.⁵⁴² That is a dose-response surface rather than a demonstration, and the reason for the extra axes is stated: at higher oxygen, temperature and humidity become very critical.

Two of its warnings belong in this trade and are not in it. The first is that treatment success depends on reaching temperature throughout the object rather than in the freezer air, that a warm centre means an incomplete treatment however the display reads, and that performance should be monitored with a separate thermometer.⁶⁸ Our own articles on heat treatment describe exactly this problem with the sign reversed, and this sector puts it in the protocol rather than in the caveats. The second is that previous temperature history affects cold tolerance, which our bed bug article measured as rapid cold hardening and which implies that how an object is cooled may matter as much as how cold it gets. Neither source connects those two findings.⁶

And there is the part that is not a lesson but a warning. Collections were treated for decades with heavy metal pesticides and later with fumigants. Those treatments did not fully protect them from infestation, and they are still in the objects, so anybody working with the material has to know what was applied for their own safety.¹ The pesticides outlasted the pests. A record of treatment became a safety document, which is an argument for documentation that no commercial pest control contract has ever had to make. None of this makes the sector better at pest control than anyone else; it makes it a sector whose constraints forced a rigour that convenience has not forced elsewhere.

References

1. Integrated pest management page for collections, published by a major natural history museum. Institutional guidance material. Source for the statement that the two most common procedures for dealing with infestations at the specimen or collection level are low-temperature freezing and low oxygen anoxia treatments; for the statement that many large collections have been treated in the past with heavy metal pesticides and in more modern times with fumigants but that these do not fully protect them from infestation; for the warning that researchers must be aware of the history of pesticide and fumigant use for their safety; and for the preventive recommendations to use inert materials for specimen storage such as polyethylene foam rather than cotton wool, to use well-sealed storage cabinets, to keep relative humidity low, and to consider micro-environments where collections must be stored in damp places such as basements. https://www.amnh.org/research/science-conservation/preventive-conservation/agents-of-deterioration/integrated-pest-management
2. Controlled atmospheres against insect pests in museums, a review, read as an abstract and associated summary text on a paper-sharing platform rather than in full. Source for the statement that controlled atmospheres using nitrogen represent a safe and effective method for both objects and human health; for the account that the recommended protocol suggests an oxygen percentage below one per cent for at least three weeks; for the observation that the major practical problems of controlled atmospheres are connected to treatment time and low oxygen percentage, making more flexible protocols at higher oxygen percentages or shorter times desirable by exploiting temperature or relative humidity; for the statement that at oxygen percentages higher than those commonly used, temperature and relative humidity are very critical to insects' development and success; and for the reported evaluation of modified atmospheres including argon and nitrogen against larvae and adults of two named museum species, determining lethal times at twenty and thirty degrees, finding that argon achieved higher mortality than nitrogen for both species and that adults were more sensitive than larvae with mortality generally higher at elevated temperature. https://www.academia.edu/31006786/Controlled_atmospheres_against_insect_pests_in_museums_a_review_and_some_considerations
3. Thermal methods of pest eradication and their effect on museum objects, read as summary text on the same paper-sharing platform alongside related abstracts. Source for the statement that the most common physical treatments use temperature extremes, heat above about forty degrees and cold below about ten, and that other physical treatments commonly include controlled or modified atmospheres. https://www.academia.edu/28317490/Thermal_methods_of_pest_eradication_Their_effect_on_museum_objects
4. Article on eradication of insect pests in museums using nitrogen, published in a regional conservation association newsletter. Professional association material. Source for the statement that work in 1991 proved the efficacy of using nitrogen with less than 0.1 per cent oxygen to kill all life stages of the ten commonly found museum insects studied; for the note that although it is possible to maintain a 0.1 per cent oxygen concentration this may not be easily achievable in museums for large applications; for the description of a sponsored extension of the insect mortality study at higher oxygen concentrations, evaluating the effect of relative humidity on mortality of two named common museum insects at 33, 55 and 75 per cent relative humidity in a nitrogen atmosphere with oxygen concentrations of 0.3, 0.6 and 1.0 per cent; and for the conclusion that using nitrogen gas to attain low oxygen atmospheres is a feasible alternative to toxic gases. https://cool.culturalheritage.org/waac/wn/wn15/wn15-3/wn15-307.html
5. Annotated integrated pest management bibliography hosted by a conservation information resource. Bibliographic and summary material rather than primary research. Source for the entry describing a 1991 report determining that atmospheres low in oxygen but rich in nitrogen, at 0.4 per cent oxygen with the balance nitrogen, were effective in killing laboratory cultures of webbing clothes moths, cigarette beetles, drugstore beetles and a carpet beetle species, with the method described as promising because it is relatively easy to accomplish, nitrogen is not toxic and it is considered to have little effect on museum materials; for the existence of a companion 1991 paper on the effects of low temperature on the drugstore beetle; and for the entry on an article covering the history of pest control techniques in a major collection, described as helping conservators understand that a variety of materials may have been used historically on objects in their care and as supporting recommendations for improved documentation of treatments and health safety precautions for people working with collections. https://cool.culturalheritage.org/byauth/jessup/ipm.html
6. Comparison article on nitrogen anoxia and freezing for museum pests, published by a commercial supplier of environmental control equipment. Trade material describing a national conservation institute's guidance, which we flag because several specifics in this article rest on it rather than on that guidance directly. Source for the statement that professional guidance from a national conservation institute treats both methods as established non-chemical pest control options; for the statement that species, life stage and previous temperature history can affect cold tolerance and that the object needs time to cool through its full thickness; for the low temperature guidance range of roughly minus twenty to minus thirty degrees with exposure periods commonly around one to two weeks depending on protocol; for the stress that treatment success depends on reaching the required temperature throughout the object and not just in the freezer air, with the note that if the centre remains warm the treatment may not be complete even though the display shows the target temperature; and for the handling practice of enclosing objects in a suitable vapour barrier bag or equivalent before freezing and allowing the sealed object to return to room temperature before opening. https://sinoalta.com/resources/blog/anoxia-vs-freezing-museum-pest-control/
7. Post on anoxia for museum collections, published by a heritage preservation practice. Professional blog material. Source for the statement that thermal treatment is limited to museum objects that contain thermally robust materials; and for the account that atmospheres with low concentrations of oxygen had been used for the control of pests in stored food products for several decades before the method was adapted to museum artifacts in the late 1980s, with considerable research on the efficiency of modified atmospheres for stored food pest control conducted since about 1970. https://heritagepreservationatelier.com/2017/06/15/anoxia-for-museum-collections/
8. Integrated pest management training document on remediation, prepared for a conservation training programme and published by a museum pest working group. Professional training material. Source for the note that commercial hardening freezers in vertical or horizontal configurations are designed to operate at about minus forty-two degrees and may not be much more expensive than standard commercial freezers; for the recommendation that performance be monitored with a separate thermometer, that the freezer be well insulated and that adequate air circulation be provided inside it around objects; for the reference to a heat treatment method developed at a national conservation institute using sunlight to produce temperatures lethal to insects; and for the note that buildings and large installations can also be heated with hot air. https://museumpests.net/wp-content/uploads/2017/07/08-IPM-Remediation-Winterthur-2017.pdf