B.T. TATHAMB.T. TATHAM is a member of the Alginate Industries Ltd., London.
Fire has always been both a friend and an enemy of the forester. Uncontrolled, it can ruin the work of years and cause great financial loss. Controlled, it can be a valuable tool for clearing operations and the establishment of fire breaks.
The technique of controlled burning against a secure base line has long been known and practiced. However, it is the problem of providing a sufficiently secure base line when no natural one exists which has made this method so risky and which has inhibited its use.
The use of so-called chemical fire retardants has lessened, if not entirely removed the risk, and now firecol sodium alginate solutions - viscous water - have improved the situation to such an extent that the technique can be used far more widely and safely.
The principle of viscous water is to make ordinary water into an effective fire retardant. Ordinary water is an adequate fire extinguisher but a poor fire retardant. As a result of its low viscosity, most of the water applied to a potential fuel runs to the ground and only a small proportion is retained on the vegetation or brash. Relatively little heat is therefore required to dry the fuel again. The result is a barrier which is only effective for a matter of minutes and even then will only contain fires of very low intensity. If, however, the viscosity of the water is raised, as it is in viscous water, the quantity retained by the fuel is greatly increased and almost all the water applied is actually doing work by lowering the temperature of the fire. The result is a safer and more persistent barrier.
Sodium alginate, the basic component of viscous water, is a long chain polymer which is extracted from seaweed, where it is present in an insoluble form. Dissolved in water, processed sodium alginate has great thickening power, the degree of which depends among other things on the concentration and the particular grade used. In solution it is nontoxic to animals or plants, nonabrasive and noncorrosive. It is generally sold as a dry powder, of which Firecol D.P. is an example, but it is also sold as Firecol Suspension which is a special, very readily soluble suspension of sodium alginate in a nonaqueous liquid; both of these grades are high viscosity types.
From 1958 to 1961 the Forestry Commission of Great Britain carried out exploratory trials with several potential fire retardants and came to the conclusion that monammonium phosphate and sodium alginate solutions were eminently suitable materials. This work has been described by Connell and Holmes (1963).
Since 1961 the commission has carried out further investigations of the economic and technical aspects of these two chemicals, with emphasis on sodium alginate solutions made from Firecol brand sodium alginate.
The policy has been to carry out all trials, on whatever scale, in the field on natural fuels in natural conditions. No attempt has been made to qualify the results, as this would be almost impossible; however, many replicated experiments have been carried out in which comparisons of what might be termed "stopping power" have been made between solutions of sodium alginate and water.
The main variables examined have been viscosity, rate of application in terms of volume of liquid per unit area of fuel of approximately equal depth, and fuel type, though the latter has been largely confined to heather, gorse, and molinia grass, which are the worst fuels with which the British forester has to con" tend. Some testing on brash has also been carried out.
This programme of comparatively small-scale testing was carried out during 1962-64. When it was concluded, it became possible to specify fairly closely all the conditions relevant to the use of the material in practice.
During this period of testing, machinery suitable for making up solutions in the field was also being developed, and at the end of the period had reached a sufficiently advanced state to be issued to five specially selected and trained teams of foresters for full-scale field trials in England, Scotland and Wales. These machines used the more expensive Firecol Suspension.
A detailed account of every controlled burn carried out by each of these teams for the three seasons was obtained and the results studied.
Viscous water made from Firecol sodium alginate is undoubtedly an effective, convenient, and relatively cheap fire retardant, and its use for controlled burning will now become standard practice in many of the com mission's forests. It is also the intention of the Forestry Commission to perfect techniques for using viscous water for the control of wild fires as a natural extension of the use of the material.
It was found that the cost of the retardant was offset by the savings accruing from faster working, and that some of the previously necessary provisions of the commission's fire code, which had slowed work in the interests of safety, could be modified. This has, in fact, now been done.
Since this conclusion was reached, further machinery developments have made it possible to use conveniently the cheaper Firecol D.P. with the result that an overall saving will be made by using the fire retardant.
Although attention was paid to the development of suitable machinery from the early stages of the investigation, it was not until the testing of viscous water itself was fairly far advanced that any firm ideas about the matter could be formulated. Eventually it became evident that ideal machinery for the purpose would have to be selected by considering several sometimes conflicting criteria, the relative importance of which might vary from country to country, and from district to district.
The most important of these criteria are:
1. The machine must rapidly make solutions from the cheapest form of sodium alginate.2. It must be easily transportable or even portable.
3. It should be entirely self-contained, and not rely on outside power sources.
4. It should be designed to operate from, without being an integral part of, the smallest commonly available vehicle suitable for traversing difficult country.
5. Its water carrying capacity should be as high as possible within the limitations of (4).
6. The pump and engine should be suitably rated for conditions of work, and should not be unnecessarily large.
7. It should be robust, easily serviced, and use a minimum of special parts.
8. It should be reliable and simple to operate.
9. It should be cheap.
The first piece of operational equipment used by the Forestry Commission consisted of a petrol-driven centrifugal pump, fitted with a comparatively sophisticated metering system for injecting sodium alginate in the form of Firecol Suspension continuously into the water stream at a preset but variable rate. This machine, known as the Hathaway Continuous Viscous Water Pumping Unit, has given good service for the last three years.
Its main advantages are that it can deliver plain or viscous water at will from any water source and, though fairly heavy, can be carried by two men since no water tank is required. It may prove extremely useful for delivery by helicopter into areas which are otherwise inaccessible, and which have abundant natural water in the form of lakes or streams. On the other hand, to gain these advantages, the rather more expensive Firecol Suspension must be used.
Although many of the mountainous districts of Scotland and Wales can often be as inaccessible to wheeled or tracked vehicles as anywhere in the world, it was nevertheless found in practice that the importance of portability under British conditions had tended to be overstressed. Examination of the returns from the viscous water teams showed that, in the great majority of cases, the machine had been operated from a vehicle or trailer on which a temporary water tank had also been placed, and only rarely used in its fully portable role.
The use of trailers did not prove satisfactory, owing to their lack of manoeuvrability and tendency to get stuck in soft ground. It was therefore decided to develop an alternative piece of equipment which would consist of a pump and tank unit capable of rapidly making up batches of viscous water and which could be slid into the back of the short wheelbase Landrover, which is the smallest common cross-country vehicle available to the Forestry Commission. Any idea of a specialized, single-purpose fire control vehicle was discarded because of the low utilization rate to be expected. Designing on the smallest Landrover ensured that the unit could be used on any larger carrier which might be more easily available at any time, and therefore fit in better with the general work pattern.
Once the carrier vehicle was chosen, tank capacity was fixed fairly closely by weight limitations. Although the desirability of carrying as much water as possible at one time to the scene of operations was clear, it was equally clearly limited by the availability of suitable vehicles, and indeed by the sheer impracticability of transporting really large loads across rough country.
The unit which has been evolved on these lines, and which has now become standard equipment within the Forestry Commission, is known as the Firecol D.B.60. It has a tank capacity of 60 gallons (272 litres) and is fitted with a self-priming centrifugal pump rated at 4600 gallons per hour, 90 foot head (20880 litres per hour, 27 metre head). It will make a tankful of viscous water in under five minutes. It can pick up water from any source. The machine can also be used for spraying herbicides, and general pumping, both of which increase its utilization rate.
Although this is basically simple, consisting merely of wetting a continuous strip of vegetation with viscous water at a suitable volume per unit area, the skill of the nozzleman is of very great importance, and he must thoroughly understand the underlying principle and the limitations of the method.
First the chooses a general line in the vicinity of the area which is to be protected from the fire he is about to start, and which will become the inside edge of the final burnt-out fire brake.
He will make the end secure by starting, if possible, at a point where natural conditions prevent the spread of the fire, for example, on a rocky outcrop or a beaten track. The line he chooses will not necessarily be straight, but will take advantage wherever possible of areas of sparse vegetation, animal tracks running in the right general direction, and similar very local features. He will avoid going through dense vegetation if he can. The amount of viscous water laid down will be varied to suit the changing vegetation density, putting down more and increasing the "trace" width in dense fuel, and decreasing it in less dense areas.
He will choose a day for the operation when the wind is only light and blowing away from the area to be protected on the side he intends to burn. Where front fires have to be burnt, that is to say with the wind blowing across his intended line toward the plantation, a rather wider and heavier trace must be laid and normal precautions taken against flying sparks.
After about 20 yards or metres of trace have been laid, the fire is started at the end of the trace and as close to it as possible, on the side remote from the plantation. The firelighter then proceeds along the trace, lighting as he goes, at the same rate as the nozzleman is advancing in front of him. In this way maximum speed and minimum fire front are achieved, and the progress of the fire away from the trace can easily be controlled by hand or, if necessary, by the simultaneous laying of a parallel trace at the required distance from the first.
Eight to ten men, including the nozzleman and the firelighter, are generally present for safety purposes, though most of the time they are to some extent unemployed.
The final fire break will consist of a continuous burnt strip of land about 40 yards or metres wide according to need.
The same technique applies whatever machinery is being used, both within the forest during brash clearing operations, and outside for plantation protection.
It is clearly possible to extend the method both to larger and smaller scale operations than are common in the United Kingdom, though the details of equipment and technique may vary widely from one country to another. Only in areas where there is no water at all, or which are inaccessible even to helicopters, is the method likely to prove useless, though the difficulties may in some cases increase costs to a point where the gains in terms of insurance against the spread of wild fire are not sufficiently large. There is little doubt, however, that the more widespread use of precautionary measures of the kind described could save much valuable property.
Having described the development of viscous water as a fire retardant, it should be noted that there are other uses in forestry for solutions of sodium alginate, which are proving to be of considerable interest.
Recent work carried out in the United Kingdom and, more particularly, in the Federal Republic of Germany strongly indicates that, if the roots of transplants are dipped into an approximately 1 percent by weight solution of sodium alginate, thereby picking up a considerable weight of water, they can survive at least two days of exposure to strong drying conditions before being replanted. It is reported that the survival rate after planting of transplants treated in this manner was several times better than that of untreated controls, and also that growth was put on during the first year in the field. Nursery transplants similarly treated by the Forestry Commission of Great Britain, notably Sitka spruce 1 + 0, have survived when moved at the beginning of a complete drought of several weeks' duration, without any watering, at least as well as similar untreated controls which were given the equivalent of a ½ inch (1.25 cm) of rain per week throughout the period. Although recommendations about the use of sodium alginate solutions for this purpose can be made, details of the experiments are yet to be published by the workers concerned, and it is not the intention of this article to anticipate the publication of any such paper.
Sodium alginate can also be used to thicken solutions of certain herbicides with a view to reducing drift and increasing retention on the plant, particularly where "spraying to runoff" is necessary. Two such commonly used herbicides are 2.4.5.T and 2.4.D. Not all herbicides are compatible with alginate solutions, however, and small-scale laboratory testing should always be a preliminary to any larger scale trials.
CONNELL C.A. and D.G. HOLMES. 1963, Chemical aids in forest fire control, Forestry 36, No. 1.
DAVIS J.B., D.L. DIBBLE, C.B. PHILLIPS and R.S. McBRIDE. 1962, Viscous water and algin gel as fire control materials. Pacific S.W. Forestry and Research and Experiment Station, Technical Paper No. 71.
