• flRE-PROCflNC WOOD WITH CHEMICALS 1933 ORY Nc. R1141 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin II] ; FIRE PROOFING T /OCD "I7H CHEMICALS* By G. M. HUNT In Charge, Section of Wood Preservation and T. R. 7RUAX Senior Wood Technologist She need for increasing the resistance to fire of lumber and structural timber is obvious, While it is true that the fire hazard of wooden structures of v/idely different types can be reduced by proper methods of design and construction to the point where they are reasona": safe, it is also true that effective and economical treatments of wood to reduce its inflammability would increase the fire safety of wood struc- tures and permit the use of wood in places where its combustibility now excludes it. Tho- problem has been recognized for centuries and hundreds of different fire-retarding coatings and impregnating soulutions have been proposed within the last 200 years k The majority of the proposals have been based upon inadequate knowledge, and are ineffective, too expensive, or fcr some other reason impractical. Some of the impregnation methods, however, have sufficient effectiveness and practicability to have found commercial use. It is possible now to buy commercially fire-proofed wood so resistant that it will not of itself support combustion. Effective 1 , treated wood can be destroyed only by continuous exposure to heat from an outside source; when the heating is discontinued the burning ceases. In contrast with untreated wood the difference is of the greatest prac- tical significance. Fire-Proofed Wood Defined The term w f ire-proof as applied to structural materials is technically incorrect. Even stone, concrete, and metals are destroyed when exposed continuously to sufficiently high temperatures* Wood treated by the moat effective methods known is destroyed in time by chemical de- composition if the surrounding temperatures are kept sufficiently high. Popular usage, however, employs the terms "fire-proof", "fire-proofed", . i "fire-proof ing" in connection with wood in the sense that the treated v/ood will not support flame or contribute to its own destruction. Con- v. nient words that arc technically correct are lacking, especially as substitutes for "fire-proofed" and "fire-proofing." The popular terras will, therefore, be used in this article with the meaning defined above. •Publish Proc. of the 5th Pacific Science Congress, 1933* HllU5 ,1_ Commercial Impregnation Treatment:; Although good quality, commercially fire-proofed wood, treated "by impregnation processes is available, it is not extensively employed. Its use in North America is limited for the most part to wooden floors, doors, and trim in largo office buildings of fire-proof construction in the city of New York,— Its limited use is due not to lack of fire resistance, but to its relatively high cost. A contributing limitation is the fact that fire-proofing processes are not standardized and generally known, The various fire-proofing companies presumably use different formulas although it is not possible to be certain of this for the formulj s r kept secret. There is also considerable secrecy as to their methods of impregnating the wood and of drying it afterwards. A further limit! i factor is the lack of accepted standard methods of measuring the effective- ness of the treatment. The obvious advantages that would accrue from the widespread use of adequately fire-proofed wood justify considerable effort to overcome these obstacles. Research in Fire-Proofing Research has not been entirely lacking in the field of fire-prooj ing wood, as a review of the literature on the subject "ill show.fi'l'- The various investigations reported have contributed much to the genera}. knowledge of th subject and have laid foundations for further progress, but none have resulted ir. a sufficiently convenient satisfactory and inex- pensive method of fire-proofing wood, nor have any produced testing and control methods that are generally accepted and satisfy the needs of prospective purchasers of fire-proofed wood. Unless the benefits of a more extensive use of fire-proofed wood are to be abandoned much addi- tional research must be done. The. U. S. Forest Products Laboratory at Madison, Wig., early recognized the importance of f ire-procf ing studies and undertook some work in this field. The results of its findings in these earlier studies were published in 1315.2 The continual demand for information on the subject ilngberg, S. E. Shf ety Eng. , V.53, No f 1 , pp. 29-35. 1927. ^.Truax, T. R. and Harrison, C. A. Trans. Amer. Soc. Mech. Engrs Uarratt, G-. A. Araer. Lbrman. , N0.2713, pp. 56-7; No.271^, pp. 52-3, 1927, gberg, S. E. Safety Eng. , V.53, JTo,i; 3 uax, T. R. \nc\ Harrison, C. A. Trans. A Wood Ind. , 7.52, No. 17, pp.33-^0, 1930. u -Woolson, I. I-!. Rot;. Froc- Inter. Fire Prev. Congr. , p. 257, 190^. -Prince, R. 3. Proceedings of the. Natl. Fire Protect. Assn., pr^.lOS- 58. 1915. R11^5 -2- and th obvious need for improvement in fire-proofing and fire-testing technic Causotf the Laboratory to take up the- investigation again in I927. it Products Laboratory ont rtalns no delusion that its studies will the obstacles to the extensive use of fire-proofed wood, but hopes that its contribution^ , added to those of other investigate. , will bri -ired objective definitely nearer. Sever--.] reports_«2»Z of the pr raad.e in the recent investigations have thus far b published. The work will undoubtedly continue for several years. ?ire-Rctnri?nt Chemicals Although fire-proofing companies do not make public their fermul there is reason to believe that the monobasic and dibasic phosj. I of aannonl quite generally used in impregnation processes throughout t world and that one or the other constitutes an Important part of mos* commercial formulas used in fire-proofing by impregnation. Other ch mic-ls r added for different purposes according to the ideas of the respective companies or inventors and there may be some good formulas in use that contain no ammonium phosphates. The chief advantage of the ammonium phosphates is th effectiveness in retarding the combustion of wood, coupled with the fact that they do not give the wood undesirable properties to a sufficient degree to make the use of the treated wood impracticable. There arc many chemicals that have sufficient fire-retarding ability to be used,— if it were net for their undesirable properties. Calcium chloride, fcr exampl , attracts moisture end under conditions of high humidity would tend to keep the wood too damp if used in sufficient quantities to get good fire resistance. Some chemicals attack the wood and reduce its strength, so destroy or interfere with paint and varnish adhesion, some discolor the wood or make it too hard to work with edged tools, some interfere with gluing, or are poisonous or too expensive, and practically all that ar in commercial use are too easily leached from thowood to remain permanently effective when used out of doors. Altogether, the requirements are so rigid that no single chemical thus far meets them. Mixtures of ehemiei offer greater promise of meeting these requirements than single chemicals and it is quite possible that, in due course, highly effective, nonl .g, and otherwise acceptable treatments will be possible at moderate cost. In many places where fire-resistant wood is desired, resistance to dec- jts is also important. In developing fire-proofing formulas this should be taken into consideration. It should not be difficult to include in the mixture some tcxic chemical which by adding ^ _____ _ -Truax, Hun . n, Baechler. Proc. Amor. '.\ T ood-Pres. Assn.. 726, | . 130-6U, 19305 V.27, pp.loU^Ul, 1931; V.28, pp. 71-93. 1932. 7.29, 19 7 1 ■^Pruax, T. R. Ihc fire-proofing of wood, Proc. ffatl* Fir pp. 18 _ , 1931. RI1U5 resistance to decay and insects would materially increase the value of the treated wood and thus help justify the cost of treatment. One of the chief disadvantages of the more desirable of the present fire-retarding chemicals is their cost. The quantity required per cubic foot of wood is so large that the cost of the chemical has probably been the largest single item of cost in the production of commercially fire-proofed wood. For a high degree of effectiveness approximately four pounds of the more effective chemicals are required per cubic foot of wood, or perhaps 300 pounds per thousand feet board measure. The cost of the chemical alone may, therefore, increase the cost of the lumber from $1^ to $25 per thousand feet. When the necessary treating, drying, and handling costs, plant depreciation, and profit are added, the selling- price of thoroughly fire-proofed wood may, even under present conditions, easily exceed that of similar untreated wood by $Uo to $50 per thousand foot board measure. The cost of the treated wood then becomes so high that it sharply limits the extent to which fire-proofed wood is used. Application of Fire-Proofing Chemicals Methods of applying fire-proofing chemicals to wood vary from simple surface applications and coatings to thorough impregnation. Obviously there can be a wide range in the costs of such treatments, the degree of effectiveness obtained, the ease of application, and the equipment required. At the one extreme is wood that ignites and burns almost as easily as though untreated and at the other extreme wood that ignites at higher temperatures and burns only when a considerable quantity Of heat is supplied from an outside source. There are intermediate treatments which reduce the hazard of untreated wood and which may ultimate! 1 / find a largo field of usefulness. The choice of a method of protecting wood against fire must be based upon the requirements of the use and such practical considerations as cost and convenience. Surface applications vary considerably in effectiveness, but are not dependable where severe fire exposure continues for some time. A thick coating of suitable composition may delay ignition and spread of flames for a long time when the fire source is small, but when exposed to a large fire their retarding ef fee t is only temporary* On the other hand, coatings can be applied to wood in place, or to fabricated products, by brush, spray, or dipping methods with very little equipment. They are relatively cheap and their use requires no technical training or experience. Coatings offer the opportunity of reducing the hazard of wood by decreasing the number of fires starting from small sources and by decreasing the rate of spread in the early stages of a fire. The methods and apparatus used for injecting fire-proofing chemicals into wood arc practically the same as for injecting preservatives. The wood is scaled within a treating cylinder and the treating solution forced in b->- means of pressure. If the treated wood is to be used for purposes that require no cutting after treatment, a moderate degree of RHU5 _1|_ ^er.etration may "be sufficient even though a core of wood la the center of each piece nay remain un impregnated. T fhen the lumber must be cut up o smaller pieces after treatment, or must he moulded or shaped In such a way that a considerable depth of wood is removed from the surface, complete penetration is a necessity. The effectiveness of the chemical would be largely dissipated if the subsequent cutting exposed any con- siderable areas of untreated wood. The deep-penetration requirement complicates considerabl problem of the commercial fire-proof er, for wood i3 generally much more resistant to deep impregnation than is commonly supposed. The sapwood of most commercial woods is not difficult to treat and when all-sapwood lumber is available it offers no serious treating problem. Most lumber, however, contains some boards that are all heartwood and many boards of mixed sapwood and heartwood. Such material, especially in species wi1 highly resistant heartwood like white oak or red gum, thoroughly tests the skill of the most experienced treating engineer. Complete ! tion of the heartwood in lumber over one inch in thickness requires great care and watchfulness as well as skill. The temperatures and pressures used may easily be made so severe that the lumber is rui during the treating process. These strict limitations naturally affect the treating costs. Evaluating ?ire-proof Treatments Two of the difficulties in the way of more extensive use of fire-proofing treatments for wood are the lack of standard methods of test and the difficulty of interpreting the results of tests In terms of performance standards. Until adequate progress is made alon