Andy Spate1, Elery Hamilton-Smith2, Lana Little3 , Ernst Holland4
1NSW National Parks and Wildlife Service, P O Box 733, Queanbeyan, NSW 2620, Australia
2Rethink Consulting, P O Box 36, Carlton South, Victoria 3053, Australia
3Queensland National Parks and Wildlife Service, P O Box 38, Chillagoe, Qld 4871, Australia
4Jenolan Caves Reserve Trust, P O Box  1495, Bathurst, NSW 2787, Australia

I think that we have opened Pandora’s box, taken out a can of worms and thrown it at a hornet’s nest (Anon, NSW NPWS, 1996).

The term ‘Best Practice’, or even ‘World’s Best Practice’ has become the latest buzzword of industry.  Often, it is clearly just a lot of hype to try and convince us that the same old mediocrity has been magically changed by using the right words. People are rightly beginning to be very suspicious and even contemptuous of the term.

However, we use it in our title for good or bad, simply because there is a real possibility that it might lead to better practice if we really confront the quality of management issue. David Weston (1996) of Parks Victoria recently argued that World Best Practice is a ‘goal out on the horizon’.  This leads to the notion that best practice is not the current operation of any organisation, nor is it a product, but rather it is the process of continual enhancement of standards. 

Thus, a number of the practices which we will reject in the course of this paper are practices which various or all of us have supported or used in earlier years. But we have learned from those mistakes, and from the mistakes of others (which are, of course, much easier to see) and so have embarked on the search for ‘best practice’. It is now clear that much of what has been done in the past cannot be tolerated if we are to strive for ‘best practice.’  We trust that our efforts will inspire others to become more creatively and positively critical of standards in everyday practice.

This paper was originally entitled “The Use of Foreign Materials for Tourist Cave Furniture” and its origins arose from observations of the destruction of lichen and other lower plants by zinc, and perhaps cadmium, from galvanised steel pipes and wires. These observations were direct, visual qualitative assessments and plant death was seen on a variety of rocks including granite and sandstone as well as limestone. Sometimes the effects of metal sterilisation were stunning as on the extensive bleached streaks below the galvanised lookouts on Mount Buffalo in Victoria and at Davies Creek in Far North Queensland and under electric power transmission towers at Wee Jasper, New South Wales. These observations generated some concerns about the use of zinc based products in caves which were reinforced by a paper on the issue published in the United States (Jameson and Alexander 1996). 

All this prompted us to produce a paper which sets out to review briefly some best practice principles based on Charters developed to guide the use and management of cultural (the Burra Charter) and natural resources (the Australian Natural Heritage Charter) and to suggest where these are relevant to the tourist cave situation in Australia. The principles are also relevant to New Zealand and elsewhere but are not necessarily enshrined in statute or formal guidelines outside Australia. The paper also briefly reviews the pluses and minuses of a variety of materials. Additionally there is some discussion of the chemistry behind corrosion which, in cave environments, very much reduces the range of materials suitable for use in our show caves.

Much more investigation into the extensive range of materials potentially available for use in caves is required and we hope to expand on the material presented here in future publications. We welcome any and all comments and feedback on the discussions presented herein.

When the paper was presented at Waitomo it was clear that some listeners were regarding our comments as proscriptive and as policy statements on behalf of the Association. This is not the case — they are the views of the present authors. The ideas are in the nature of advice and it is up to individual managements to evaluate what impacts they are prepared to accept. These ideas are expanded below. 

Some Principles in Heritage Presentation.

The Australian ICOMOS Charter for Conservation of Places of Cultural Significance, commonly known as the Burra Charter, has laid down a standard set of definitions and a series of guidelines for conservation practice for use by conservation architects and others. As a result there is now a set of widely recognised principles which are increasingly observed in the maintenance, repair or restoration of built heritage properties. 

Various agencies and many individuals working in nature conservation became concerned that a parallel set of principles should be enunciated to guide practice in management of the natural heritage. This has now been achieved, and the Australian Natural Heritage Charter (1996) has been published. Even though it has provoked some criticism from those who believe it should have said more (or less) about some issues, or that it has copied some clauses directly from the Burra Charter without adequately relating them to the natural environment, the fact remains that it provides a valuable starting point for better practice. There is not time or space to summarise the whole document here, but we can at least draw attention to aspects which are especially relevant to the thrust of this paper. Tourist Caves are, of course, also places of cultural significance, so we will also draw upon Burra Charter experience.

Most basically, a place is defined as ‘a site or area with associated ecosystems, which are the sum of its geodiversity, biodiversity and natural processes’.  In brief, consideration of any cave should therefore also involve consideration of the total context within which it is located and the total of its various contents. Rolan Eberhard (1996, p.8) nicely expressed something of this in saying that karst is an integrated and dynamic system of ‘. . . component landforms as well as life, energy, water, gases, soils and bedrock.’  The kind of practice which has developed under the Burra Charter always endeavours to preserve the context of a building, and although this may be more complex in respect to the natural heritage, it is far more important.

We should also emphasise the term ‘process’. We must recognise that caves are not static, but are subject to on-going processes and ensure the continuing integrity of these.  The various definitions relating to the act of conservation all emphasise the maintenance of natural significance through protection, maintenance and monitoring. 

But to turn to engineering: 

Cl. 1.28 of the Charter states that ‘Modification means altering a place to suit proposed uses which are compatible with the natural significance of the site’ (our emphasis). A basic principle in any alteration (doors, steps, pathways, etc.) has to be therefore assessed in terms of compatibility and the absence of impact upon natural significance. 

One can only shudder at the wholesale destruction of floor deposits which has characterised tourist cave development in the past. More importantly, it means that there are many caves or parts of caves which should not have been opened to the public, and that in the future we may have to accept that it is inappropriate to open others.

Article 10 insists that elements of the natural heritage should not be removed ‘. . . unless this is the sole means of ensuring their survival, security or preservation and is consistent with the conservation policy’.  A note to this article deals with legitimate scientific collecting. Then Article 11 further states that destruction of any elements is unacceptable ‘. . . unless it is the sole means of ensuring the security of the wider ecosystem.’. 

The articles dealing with enhancement, modification and maintenance all emphasise the integrity of the natural elements and processes. In particular Article 22 argues that records must be kept of any unavoidable damage, loss or replacement to allow their future reinstatement or to guide restoration. 

Turning to the kinds of practice which have developed under the Burra Charter (NSW Department of Urban Affairs and Planning 1995) :

•  Repair but not replace. In simple terms, if a stalagmite is broken, it may be repaired to maintain aesthetic quality, but must not be replaced with another.
• All alterations must be readily reversible. For instance, all pathways and steps should be able to be easily removed without any damage to the original structure of the cave.
• Any new development must be able to be clearly distinguished from the original. There is a parallel here with the archaeologist backfilling an excavation — today this is done using clearly different or clearly ‘labelled’ soils so that any future investigation will be able to ready determine the extent of the excavation. Similarly, in a cave we should not introduce soil or rock in construction which is not readily distinguishable from that which occurs naturally, simply because it introduces confusion. Rather, we should use different or clearly ‘labelled’ materials. Further, we should not transfer materials from a ‘hidden’ or any other place in the same cave. 
• Avoid precise imitation — again a new development of any kind should be able to be distinguished easily from the original. The classic example in caves is that lighting should use, for example, metal shades rather than building rock basins to look like part of the cave. 
• At the same time, alterations or additions should be sensitive in design and compatible with the cave. Making things clearly distinguishable is no excuse for ugliness and bad taste. Thus, a further working principle under the charter is that in any work, design excellence should be sought in any new construction.
• Respect natural change and ageing. This can be extremely tricky. Dust in caves is often perfectly natural and changes which result from settling out of dust should remain. However, settling out of lint and skin flakes is not part of the natural system, but if we clean away this intrusive material with all its impacts upon the biology of the cave, we will also clean away the natural deposition. Judgement and wisdom must be used in any one specific situation — we can usefully ask which is the lesser evil?
• Respect previous alterations. If inappropriate, previous alterations would be removed if this can be done without serious damage. However, some alterations may well have assumed a cultural and/or historic significance and in this event should stay. 
• Discontinue previous unsound practices. As a simple example, it is now clear that significant pollution in caves results from previous unsound practice, such as fabrication of steps, protective railing, etc. within the cave, leaving behind a residue of metal flakes, sawdust, and other scrap materials. 

PROBLEMS BETWEEN METALS

According to Chang (1994), "corrosion is the term usually applied to the deterioration of metals by an electrochemical process", and he goes on to point out examples of the many common occurrences of corrosion in the everyday world around us — rusting iron, tarnished silver, and patinated (green) copper and brass.

This electrochemical process requires the presence of an electrolyte in contact with the metal, and a (standard reduction) potential difference either within the metal, between two different metals, or between a metal and a non-metal.  The whole then acts as a galvanic cell, where electrons are lost by the metal at the anode, producing the characteristic pitting and deterioration of a corroded metal. The cathode reaction usually involves the consumption of oxygen, so the cathodic area is usually that exposed to air.  The electrolyte, which may be simply a moisture film, allows migration of ions, and completes the circuit. 
Thus, we can better understand what conditions are more likely to induce corrosion, and what strategies we may employ to control it.
For example, a common device is to paint an iron or black steel surface, in order to protect it from corrosion.  And while the paint layer remains absolutely intact, this method is successful.  However, once the integrity of the paint layer is compromised, severe corrosion can occur due to the high potentials being generated by a very large anode area (the metal under the paint) and a small cathode (the exposed bit).  Sense a high-maintenance schedule presenting itself here?  This may be OK — if you've got lots of bored sailors around.  Plastic or other coatings of metals may be another option, but the same rules apply once the coating is breached.
Galvanising is a more effective means of protection because the zinc in the galvanising material is more easily oxidised (has a lower potential) than iron or steel, so continues to be attacked even if the metal underneath is exposed by a scratch — i.e. in this case the zinc acts as the anode.  However, as we have seen/shall see, there are other problems associated with the use of zinc. 
It is interesting to note that although aluminium has an even greater tendency to oxidise than zinc, the layer of insoluble aluminium oxide which readily forms on the surface of this metal when exposed to air serves to protect it from further corrosion.  This general principle has been applied in the process of passivation, where a thin oxide layer is formed when the metal is treated with a strong oxidising agent such as a concentrated acid, followed by an increase in pH.  In this way, treated waterpipes can continue to be protected by maintaining a slightly alkaline (pH ~8) water supply.  This would seem to be the simple solution for many cave managers' problems, were it not for the inevitable mountain of complicating environmental factors.
As described, a potential difference is necessary for a galvanic cell to operate, and therefore for corrosion to occur.  Unfortunately for us, such differences in potential are ridiculously easily generated within the 'normal' environment of a cave.  If different areas of a piece of metal — let’s say a pipe handrail — are exposed to different conditions — say, partly set into the earth, and partly exposed — then a potential difference can occur. 

It cannot be stressed strongly enough that use of dissimilar metals in contact, within a moist environment, will always induce corrosion. 

This is so even down to the scale of different alloys of the same metal — e.g. different grades of aluminium.  However, if you've been caught by this one, don't despair — but do act quickly.  The first and best solution is not to use dissimilar metals; the next is to isolate the materials from each other using simple devices such as neoprene or nylon washers. this may only delay the inevitable if a water film is present across the barrier. If it's not possible to insulate the metals from each other, then consider the use of sacrificial anodes.  The anode will always be the most active metal — i.e., the lower potential, or the more readily oxidised.  In this way, strips of metal such as zinc or magnesium are often employed to protect the steel hulls of ships.  It is not necessary for the sacrificial material to completely cover the metal to be protected  — it must simply remain part of the circuit. But, remember that your sacrificial anode will be producing some sort of chemical compound(s) which may have adverse effects on the cave or its contents.
If you are fortunate enough to manage dry, or even seasonally dry caves, corrosion will be far less of a problem than for those who have predominantly damp conditions to contend with. But beware the sneaky threat — stray currents!  In this scenario, the electromotive force is provided by an external source, rather than being generated by differences in potential occurring naturally in the materials. (So in this case we actually have an electrolytic cell.)  If the leakage is great enough, the results will be out of all proportion to those expected to arise from purely environmental factors.  For instance, the problem is said to be severe in Melbourne waterpipes experiencing current leakage from tramlines.  While we are not aware of any cases within caves where accelerated corrosion can be attributed to this cause, it's probably another good reason to opt for low voltage supplies.  If you seriously think you've got a problem with this one, the quick-fix is to apply a DC current directly to the metal in the reverse direction to the leakage-induced flow, so converting the metal to a cathode.  Good luck with Work Place Health and Safety implications.
To sum up, corrosion prevention/control may be attained by use of corrosion-resistant material where feasible, maintaining metals in as dry an environment as possible, insulating them from contact with the air or other materials of differing potentials, and safeguarding them from stray currents.

PROBLEMS BETWEEN NON-METALS

Interestingly, problems can also arise between non-metals if there are chemical inconsistencies. For example at Yarrangobilly caves there is a sandstone commemorative tablet attached to a pillar of limestone blocks cemented together with a mortar of unknown type. The limestone contributes calcium ions and sulphate ions come from the sandstone and perhaps the mortar. Repeated wetting and drying causes calcium sulphate (gypsum) to crystallise or redissolve in the tablet. This is causing breakdown of the tablet at a rapid rate. This sort of reaction between different rock types is a very common cause of breakdown of building stones (George Gibbons, NSW Dept of Mineral Resources, pers. comm. ) and may occasionally cause problems in karstic environments.

Some Structural Considerations

None of the present authors are engineers and thus we can give no guidelines for structural issues from safety, strength or durability viewpoints. However, we can suggest a few ideas for better engineering work practice from an aesthetic point of view. The following may be of value:
 

• Curves are better than straight lines and oblique and acute angles.
• Chains, wire ropes and the like look better when hung in catenary rather than being strained tight. Exceptions to this are “belly wires” and intermediate wires below handrails whether rigid or in catenary.
• Remember that tread meshes in platforms and steps will clean mud etc from footwear and those metal meshes that provide the best grip will also shave the rubber from visitors shoes. The next problem — rubber shavings! Consider using catch trays or not using such meshes.
• Remember that the cave tourist does not see (within reason) what the cave manager sees. Over-camouflaging can sometimes be counter-productive and equally as obtrusive as the original material.
• Colour correction can be a very great advantage. Matt surfaces in black, brown or grey markedly improve the aesthetics of installed structures ... but what are the environmental implications? Sometimes the strong visual impacts of the materials may add to the cave scene as evidenced by the very positive reactions of the visiting public to the aluminium handrails and stainless steel wires used in Jersey Cave, Yarrangobilly.

Here we discuss a range of materials used, or potentially useful, in show caves. The discussion is not exhaustive. Some of the pros and cons discussed here arise from experience; some from the literature; some are of the nature of hypotheses and others from an understanding of the chemistry of the materials.  It has proved difficult to obtain adequate technical data on many products and the comments here should be regarded as preliminary unless sources are quoted. Some of the materials are in common use; others have considerable potential to damage or enhance the cave environment. We welcome feedback on any experiences with old, new and potentially useful materials. Again we emphasise that these are ideas for managers to consider within the confines of their own operational constraints be they environmental or fiscal.

METALS
 

• Aluminium

A number of aluminium alloys are especially manufactured so as to be stable in alkaline environments and these may be able to be used successfully in caves. However, experience at Yarrangobilly has shown, in spite of the supplier’s claims to the contrary, that fittings said to be of the same alloy are quite different and electrolytic corrosion is destroying the much-admired aesthetics of the material and will ultimately destroy its structural integrity.

• Iron and steel

•  Black/mild steel

•  Galvanised steel

Observations of problems produced by the leaching of zinc and possibly cadmium and related toxic metals on lichens, other lower plants and on invertebrates have suggested that we should use such materials with caution in our sensitive underground environments. Jameson and Alexander (1996) have recently examined this issue quantitatively and suggested that leaching of galvanised coatings may have adverse impacts on invertebrate cave faunas and on calcite deposition. Certainly leachates from zinc structures have markedly affected the flora on many rock types in many environments ranging from Chillagoe to Mount Buffalo in Victoria.

Cutting, bending or welding of galvanised products will destroy the integrity of the galvanised coating to a greater or lesser extent. As explained above once the coating is substantially breached the situation may well be worse than with uncoated steel because of the creation of electrolytic effects.

•  Stainless steel

However, we believe that cave managers will increasingly be using stainless steel for in-cave applications.

•  Wrought iron

•  Cast iron

• Non-ferrous metals

Lead and, to a lesser extent, brass fittings have also polluted cave environments in many areas. In most caves such metals are completely foreign to the cave environment and their use should be avoided.

• Metal coatings

TIMBER 

The use of timber in caves should normally be avoided although there are very many occasions when its use has been remarkably successful. It is often aesthetically effective (or perhaps less aesthetically impacting than concrete or metal). Almost all forms of timber break down relatively rapidly in cave environments; many will bring large quantities of nutrients into the cave ecosystem with possible far-reaching effects. Often the various slime-mould, fungi and similar lower plants which take advantage of the new-found bonanza of food are aesthetically unpleasant and can be very difficult to remove. As some timbers age they may exude sap and other liquids which can stain and perhaps be toxic.

If any form of timber is used for formwork, scaffolding and similar temporary purposes it should not be worked in the cave if at all feasible. It should be removed on completion of the job; care should be taken to remove any scraps or splinters resulting from working the timber or dismantling the structure.

• Hardwood timber

• Softwood timber

• Treated timbers

If CCA treated timbers are to be used in sensitive environments, above or below ground, they should be allowed to weather for several months in an exposed, but environmentally robust site. Comfort points out that material is very quickly, and more effectively, leached from shavings and drill cuttings than from the solid logs. Thus fine materials should be collected rather than allowing them to enter the environment inside or outside caves.

• Manufactured timbers

CLAY/STONE MATERIALS

Clearly this class of materials are most like the natural products within caves. However, this does not mean that they are entirely benign nor that their use does not need careful consideration.

• Cave earth

• Cement and gypsum stabilised earth floors

• Other earth stabilising agents

• Concrete

Concrete should never be poured onto raw rock, flowstone or other natural floor materials. A plastic or similar membrane should be used to cover the floor. Microgours or similar sharp surfaces should be covered in fine sand which can be vacuumed away if the concrete is later removed. It is possible in many cases to remove concrete masses or splashes from cave interiors but there will always be damage. The path covering the black flowstones in the rear of Jersey Cave, Yarrangobilly, is a stark lesson of the hazards of concrete use.

• Low density concrete

In New Zealand there are apparently low density concretes available which use pumice as the low density component. This would seem to be an excellent concept which would produce a strong and low density and wearproof product. It helps to have volcanoes around!

CERAMIC AND SIMILAR TILES

Ceramic, terracotta and similar tiles themselves are highly suitable materials for use in caves. Unfortunately they have to be fixed to a hard substrate below. The substrate would normally be concrete and its disadvantages have already been discussed. Cements or mortars will be relatively benign. Adhesives may well present problems.

BITUMEN/ASPHALT

The use of these substances is probably highly contra-indicated underground. Many of them will leach products which are toxic to biota and which may interfere in calcite deposition. Certainly some are more benign than others but the precautionary principle should apply here unless there are very compelling reasons for their use. Many of the disadvantages of concrete apply to these materials.

PLASTICS AND SIMILAR MATERIALS

There is an enormous range of plastic (polymer) materials available today. There are many profiles available many of which are specifically designed as tread patterns and so on for use in industrial situations. We have not investigated the range of plastic products in any detail. 

Products such as nylon, perspex, lexan and similar plastics are highly inert and easily worked. Many plastics will burn freely giving rise to a variety of unpleasant compounds. PVC is used extensively for electrical cable insulation but may depolymerise under certain conditions producing toxic gas. However, we are stuck with PVC for the foreseeable future.

Plastics such as fibreglass and the carbon-fibre reinforced plastics have a definite role in the provision of cave furniture in the future as have bulk materials manufactured from recycled PET bottles. However, we would recommend against the mixing of two part plastics (epoxies and fibreglass) in caves for human health reasons as well as for the protection of the cave resource.

Astroturf and similar plastic mattings certainly have a major role in protecting caves. Their use at Yarrangobilly has been very successful in reducing the transport of dirt through the caves. It also markedly reduces the splashing from pathways to cave surfaces produced by the heavy feet of visitors, is more comfortable to walk on and is probably more reassuring underfoot than is bare concrete.

If one examines catalogues of flooring materials for industrial kitchens and factories an immense range of products will be revealed. Some will not be useful in a cave environment or may have positive disadvantages. Others will be the materials of the future. As stated above we have not begun to explore the range of plastic products and forms available and would welcome feedback on any products.

GLASSES

The recent re-engineering to provide protection to the “Tuning Fork” in Maracoopa Cave, Mole Creek, Tasmania, using glass provides a wonderful example of how innovative use of materials thought to present too many difficulties in the past. Concerns have been raised about the condensation of moisture and electrostatic deposition of dust onto glass (and plastics). The “Tuning Fork” example appears to have worked brilliantly in that environment especially from an aesthetic viewpoint. 

Glasses with ultra-thin transparent metallic coatings may well be able to cope with both of these problems by allowing the passage of electric currents to either raise the temperature of the surface above the dew point or to destroy electrostatic potentials so that atmospheric dust, lint etc. does not adhere to the surface of the glass. There is much scope for experimentation here.

Discussion

The discussion which followed the spoken presentation at Waitomo suggested that there are five major factors that must be considered in tourist cave engineering best practice. These are:

• Public and worker safety considerations
• Removability of structures 
• Aesthetics of structures
• Avoidance of toxins/pollutants
• Durability of structures

Some of these factors have been addressed in the discussion of individual materials above. Our aim in producing this paper is to provide some information for managers so that they can adopt the precautionary principle in their cave engineering practices.

We are not advocating that managers immediately, or even in the short to medium term, undertake wholesale removal all of materials from within their caves. This may do more damage than good and much of any impact arising from the leaching of zinc from galvanised netting at Jenolan, Yarrangobilly, Wombeyan or Buchan, for example, has probably happened long, long ago. What is needed is an understanding that traditional practices may not be safe and that innovations, like the use of aluminium in Jersey Cave at Yarrangobilly, may still produce problems even if the cave “engineer” thinks he or she has considered all the angles of the underground Pandora’s box.

Acknowledgements

A number of people have made valuable comments during the preparation of this paper and during the discussion which followed its presentation at Waitomo. These include Richard Mackay, Tony Little, Van Watson, Neil Taylor and others. We thank these people for their input but must state that opinions expressed herein are those of the authors.

References

Australian Committee of the International Council on Monuments and Sites (ICOMOS), n.d., The Burra Charter.  See Appendix A in Yencken, D, The National Estate in 1981, Canberra: AGPS for the Australian Heritage Commission.

Australian Committee for the International Union for the Conservation of Nature  1996, Australian Natural Heritage Charter, Sydney: Australian Heritage Commission and the Committee.

Chang, R  1995, Chemistry, 5th ed., McGraw-Hill

Eberhard, Rolan  1996, Inventory and Management of the Junee River Karst System, Tasmania, Hobart: Forestry Tasmania.

Elliott, William R  1996, The evolution of cave gating, American Caves, 9(2): 9-15.

Comfort, Michael  1993, Environmental and occupational health aspects of using CCA treated timber for walking track construction in the Tasmanian wilderness world heritage area, Tasmanian Parks and Wildlife Service, Hobart

Jameson, Roy A & Alexander, E Calvin Jr  1996, Zinc Leaching from Galvanized Steel in Mystery Cave, Minnesota, in Proceedings of the 1995 National Cave Management Symposium, Indiana Karst Conservancy Inc, Indianapolis, pp. 178-186

NSW Department of Urban Affairs and Planning with NSW Heritage Council  1995, Principles of Conservation Work on Heritage Places, Sydney: The Department, ix + 7 pp. 

Weston, David  1996, Best Practice in Park Management, in Making a Difference, Proceedings of the New Zealand Recreation Association and International Federation of Parks and Recreation Administration Conference, eds M P Wrigley & T E Arthur,  Massey University, N.Z., pp. 1-38/1-43.