| Show SOUND LONG GRAINED WOODS NEEDED IN SAFE TIMBERING OF MINE WORKINGS the kinds of timber used in mining operations are as varied as the localities in which the mines occur states the department of the interior as a result of a study of the timbering berin b of metal mines just completed by the bureau of mines in some districts in which there is a scarcity ot of good Z 15 timber such as in the southwest the prospector and small mine operator use the dwarf varieties usually found in these arid regions such as mesquite sage brush juniper cottonwood pinon etc long b grained timbers such as pine fir spruce oak and chestnut are preferred because they will crack and split when pressure comes on them and thus give warning long before they break although timbers should be long grained strong and elastic they should not be too heavy oak and chestnut and other long grained hardwoods are strong but many hardwoods are heavy to handle short grained woods are often unreliable as an indicator of dangerous pressure because they may break without warning the bureau of mines advises that the use of such flexible woods as hickory eucalyptus and willow be avoided if possible as they bend easily under tinder pressure and do not offer in proportion to their size much resistance to the movement of the rock the willow especially lacks both strength and durability those timbers of the pacific coast that are best adapted to mining users are douglas fir california fir white fir sitka and white spruce and yellow pine bull pine but western hemlock cedar and redwood also oak maple chestnut and other hard woods are used where most easily available sometimes the scorched timbers of burned over districts are used when the heart of the timber is sound these have proved acceptable they are cheaper than timber and are practically as strong in alaska there have been many objections given to the use of native spruce and native hemlock for mine timber some mining companies have preferred to ship in douglas fir from washington and oregon instead of using the native woods at present the amounts of alaskan timber being used in the mines there are much larger than formerly experiments peri ments by the forest products laboratory on sitka spruce and alaskan hemlock indicate that the better grades of these woods compare favorably with lodgepole lodge pole pine and douglas fir A fundamental principle to be kept in mind is that mine timbering should afford adequate support at least expense enough timber should be used to insure safety t to 0 the workings and to the men but as timbering is often one of the chief items of cost in mining the excessive use of timber is an economic waste timbering serves primarily by the prevention of caving and to keep the workings open for such time tirzie as is necessary for extracting the ore or for purposes of transportation por tation and ventilation when the workings are aban boned the timber therein has fulfilled its purpose and is so much waste material although some of it may perhaps be recovered for reuse in other parts of the mine because timber suitable for use in mines is becoming increasingly scarcer in nearly all mining districts and at many places must be shipped in and because of the labor cost involved and the further fact that most mine timber can not be recovered there is greater and greater need for exercising good judgment in utilizing timber to the best advantage the most important principle of mine mine timbering is to timber in time that is immediately after excavation and before the rock inside the natural rock arch becomes brok and begins to settle if this principle is followed irwill it J en save time money and many lives the ventilation of a mine has considerable effect anth the s life of the timber damp stagnant air will cause mold arid ans fungus growth which will be followed by decay and rot all timbered active places in mines should be well ventilated and special provision should be made for the removal of the damp hot air which is commonly found underground in in pumping stations and around steam lines timbers used in mines are subject to destruction from decay and insect attack breakage mechanical wear and fire it is estimated that under average conditions 50 per cent of the total timber used is destroyed by decay and insect attack decay and its accompanying evil boring by insects the most destructive agencies acting on underground timber can be retarded by peeling and seasoning the timbers before use and by treatment with a suitable preservative while it may not always be feasible for the small mine operator to use preservatives peeling and seasoning timbers is always possible bark when left on the timber retards regards the evaporation of moisture leaving timber more easily attacked by fungus growths and various vadous wood boring insects the average life of green nn unpeeled peeled and untreated timber used in amine is from one to three years but by peeling alone the life of timber when used in dry mine workings may be increased 10 to 15 per cent there are several kinds of wood preservatives which have been used successfully on mine timbers creosote zinc chloride and sodium fluorite are the ones most commonly used the bark should always be removed from the timbers before treatment |
