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(3) BEST METHOD OF FIREPROOFING WOODEN BRIDGES
AND TRESTLES C. S. HERITAGE, Chairman; E. M. LEWIS, C. H. BLACKMAN, 0. C. BADGER, Sub-Committee.
Fire protection on all classes of railway structures is of utmost importance. This is especially true of bridges. The loss to a railroad on account of a burned bridge usually far exceeds the value of the bridge itself, because the line of traffic is obstructed and the railroad does not fully function until traffic can be resumed over the burned structure.
Wood is an inflammable material and a fire hazard always exists when wooden bridges are used. This hazard can, however, be reduced to a minimum.
Your Committee has, through a questionnaire, endeavored to ascertain the practice of the various railroads in regard to fireproofing wooden bridges and the results obtained from the use of different forms of fire protection, as well as the advantages of and objections to the various forms of fire protection that had been tried.
Answers were received from fifty roads, aggregating approximately 139,000 miles.
It is well established that the great majority of railway bridge fires are started from sparks or from hot coals dropped from locomotives. From the best information available, we believe this source to cover fully ninety per cent of all bridge fires.
Other sources of bridge fires are: Fires from brush or weeds burning around bridges; forest fires; tramps; lightning; fires from oil burning on water under bridges; incendiary; fires from dropping lighted cigarettes; tires from hot coals thrown out of dining cars and fires spreading from burning buildings or other outside sources. Of these sources, other than fires from locomotives, fires from burning brush and weeds are most frequent.
From this it appears that the principal sources of fires to guard against are fires starting from locomotives and to a less degree, fires starting from burning brush and weeds.
Fires from locomotives will be guarded against if the deck is so protected that if hot coals should drop from the engines, they cannot reach the timber. Fires from burning brush and weeds will be guarded against if the ground is cleared of this growth for a sufficient distance around the bridges. If these two precautions are taken, the bridge is reasonably protected from ordinary sources of fire.
Various forms of fire protection are used on the decks of bridges to keep hot coals from setting fire to the timber, such as ballasted decks, sheet metal over ties or both over ties and guard timbers, sheet metal over stringers and caps, gravel or rock covered decks and by the use of fireresisting paint.
Of these the ballasted decks is the most favored. It has other advantages as well as being a very efficient protection against fires and its use is increasing among roads that maintain a considerable amount of timber trestles. Twenty-four roads reported using ballasted deck trestles. It is standard construction for seven roads and used extensively on several others. It is the most generally favored construction for furnishing an effective fire protected deck.
Covering decks with sheet metal was reported in use on seventeen roads, of which seven used it extensively and two reported having discontinued the use of it. It is effective when well maintained. The objections are that it is difficult to hold in place and makes inspection difficult. Also the life is not as great as the life of the structure when ordinary thin sheets are used.
Covering caps and stringers with sheet metal was reported in use by twenty-one roads. It is standard construction on seven roads. Four roads have discontinued the use of it. It is effective when well maintained but does not protect the ties. It is generally considered to lengthen the life of the timbers by keeping moisture out as well as protecting them from fire caused by dropping coals, althought one road reports that the timbers do not last as well when covered with sheet metal. If thin metal is used it does not last as long as the structure. It is subject to destruction from brine drippings. It is difficult to hold in place and makes inspection of timber difficult.
The use of a solid floor covered with gravel or crushed rock was reported in use by twenty roads but only three used it extensively. It was standard on one road and had been discontinued on one road. It protects the deck effectively when well maintained. The opinions of the various roads were divided, some claiming good results and others unsatisfactory results. The objections are that it is difficult to keep the gravel evenly spread over the floor, the vibration and draft from moving trains causing it to shift leaving bare places on the floor; it holds moisture, hastening the decay of the floor timbers; it gets under the rails and cuts the timbers, especially at the joints; it will not stay spread properly over the floor when the track has a superelevation to provide for curves.
The use of fire resisting paint was reported by 16 roads. It is used extensively on three roads and is standard on one road. It has been tried experimentally on ten roads and discontinued on one road. The general opinion is that it is effective against ordinary fires for a period of three or four years after its application, although some roads reported that it was not effective and of little value. It is probably a good protection to the timber, but to be entirely effective must be applied every three or four years. It will also keep the timber in better condition, thereby lessening the likelihood of its catching fire.
Other forms of fire protection, such as the covering of decks with roofing material, sanding or grouting the tops of ties or timbers were mentioned, but reports were too meager to draw any conclusions as to the value of these treatments.
To prevent fire starting from burning brush and weeds it is necessary to keep the right-of-way clear of undergrowth in the vicinity of wooden bridges. All brush and weeds should be kept cut at least 25 feet away from the bridges both underneath and on the embankments around the ends of the bridges and the sod removed under the bridge to a distance of at least three feet outside of any timber in the structure.
All wooden bridges should be provided with some form of fire fighting apparatus. It is usually impracticable to provide elaborate equipment for fighting a fire that has gained great headway. Our efforts along this line should be directed toward fighting fires in their incipiency, thus preventing the larger fires. For this purpose, it will usually be sufficient to provide water barrels and buckets for all wooden bridges, using one barrel for each bridge 50 feet long or less and one additional for each 150-foot length of bridge. In freezing weather the water in the barrels must be treated with salt or calcium chloride to prevent freezing: Fire buckets having round or conical shaped bottoms with a small hole in the bottom should be used. These are of less general utility than ordinary buckets and are not so likely to be stolen. On freshly creosoted structures, sand boxes with shovels can be substituted for water barrels and buckets to advantage. The sand must be kept dry to prevent freezing in cold weather. More elaborate fire-fighting facilities such as fire extinguishers, hose where water supply is available and watchman service may be provided in special cases where conditions warrant.
On overhead wooden roadway bridges, general precautions against fire should be taken as on wooden railroad bridges; that is, keep weeds and brush cut away from the timber and protect the timbers over the track where they are likely to catch fire from locomotives, by covering with sheet metal or painting with fire resisting paint.
The fire hazard on long wooden bridges can be reduced by introducing fire walls, one or more panels of concrete slab trestle, or other suitable barriers, at intervals along the bridge.
The use of creosoted timbers for railroad bridges is increasing. Timber when freshly creosoted is more inflammable than untreated timber, however, after it has been in service one or two years and the surface oils have dried out, it becomes a safer material than untreated timber.
On old bridges where timbers have started to decay, all loose and decayed timbers should be adzed off. Such conditions not only furnish a place for loading of hot cinders but timber in this condition is more easily ignited than good timber. Such conditions have been the direct cause of the beginning of many bridge fires.
Your Committee offers the following recommendations as good practice for fire protection on wooden bridges and trestles:
Recommendations on Fireproofing All locomotives shall have adequate and well maintained spark screens in the front end and ash pans shall be maintained with a tight fit so that fires and hot coals cannot drop out.
The decks of wooden bridges shall be protected from fires starting from hot coals dropped from locomotives, preferably by adopting Lallasted deck trestles; otherwise, by covering the deck with rust resisting sheet metal or covering the stringers and caps with rust resisting sheet metal.
When ties or other timbers are exposed, all decayed timber shall be kept trimmed off.
All brush and weeds shall be kept cut down for a distance of at least twenty-five feet from the bridge, both underneath and on the embankment at the ends of the bridge. Also all sod shall be removed from under timber bridges for a distance of three feet outside of the timber.
Water barrels with buckets shall be maintained on all timber briilges. one barrel each for structures up to 50 feet long and one additional barrel for each additional 150 feet.
On long bridges it is advisable to protect the bridge by introducing fire barriers at intervals of about 400 feet. This will reduce the hazard by preventing loss of the entire structure in case of fire.
Special fire fighting apparatus and watchman shall be employed in unusual cases where conditions warrant.
Bibliography on Fireproofing Trestles Fire Protection on Wooden Bridges and Trestles. Report of Committee.
Proceedings, A.R.E.A., 1913, pp. 690-697. Fireproofing for Wooden Bridges. Report of Committee and discussions.
Proceedings, Am. Ry. B. and B. Assn., 1911, pp. 47-81. Fire Resisting Coatings for Timber. Report of Committee and discus
sions. Proceedings, Am. Ry. B. and B. Assn., 1912, pp. 37-42. Railway Fire Protection Equipment Report of Committee and discus
sions. Proceedings, Am. Ry. B. and B. Assn., 1919, pp. 131-138. Fire Protection on all classes of bridges and trestles. Report of
Committee and discussions. Proceedings, Railway Fire Protection
Assn., 1920, pp. 40-49. A Manual on Fire Protection for Railroad Properties. Recommendations
for safeguarding the fire hazard at track and overhead bridges.
United States Railroad Administration Bulletin No. 8, 1919, p. 94. Discussion of paper on Fire Proofing. Transactions A.S.C.E., Vol. 65,
1909, p. 274. Fire Protection and Prevention on Railroads, W. H. Hoyt. Bulletin
Affiliated Engineering Societies of Minnesota, Vol. 5, May, 1919. Preliminary work in Fireproofing Wood by R. E. Price. American Wood
Preservers Association, June, 1914. Discussion of Inventions for rendering wood fireproof. California Jour
nal of Technology, September, 1909. Maintenance of Way and Structures, p. 294, by Wm. C. Willard (1915). How wood is destroyed by fire and most effective methods of fireproofing,
by James Scott. Railway Engineer, November, 1916. Watch the Wooden Bridge (Editorial). Railway Maintenance Engineer,
September, 1918, p. 289. Different types of fireproofing for wooden trestles, by Wm. H. Sellew.
Railway Maintenance Engineer, 1915, p. 62.
Report of Committee, Am. Ry. B. and B. Assn. on Fire Protection of
Bridges and Trestles. Railway Maintenance Engineer, November,
1919. Protection of Wooden Bridges from Fire, from report of Amer. Ry. Fire
Protection Association. Railway Maintenance Engineer, January,
1920, p. 29. Report of unusual fire on N. C. & S. L. bridge, p. 335-337; A Fire Wall
for Trestle Bridges, p. 332. Railway Maintenance Engineer, Septem
ber, 1921. Protection of temporary bridges against fire, from report of Operating
Officers Association of the C. & N. W. Ry. Railway Age Gazette,
May 19, 1911, p. 1173. Protection of Wooden Bridges from Fire. Railway Age Gazette, Decem
ber 15, 1911.