Effect of Fire-Retardant Treatments on ... - ACS Publications

6 Effect of Fire-Retardant Treatments on Performance

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Properties of W o o d CARLTON A. HOLMES Forest Products Laboratory, Forest Service, U.S. Dept. of Agriculture, P.O. Box 5160, Madison, Wis. 53705

The one m i l l i o n f i r e s i n buildings in the United States account for about two-thirds of the 12,000 people who die each year in f i r e s . The property loss i n building f i r e s i s about 85 percent of the t o t a l annual $3 billion property loss i n f i r e s (1). Building contents are often a primary source of f i r e and are usually responsible for fire-related deaths before struct u r a l members become involved. Nevertheless, wood and wood-base products, extensively used both as structural members and as interior f i n i s h i n housing and buildings, can be contributors to fire destruction. To reduce the contribution of wood to fire losses, much research through the years has gone into development of fire– retardant treatments for wood. A t o t a l of 21.3 m i l l i o n pounds of fire-retardant chemicals were reported used i n 1974 to treat 5.7 m i l l i o n cubic feet of wood products (2). The amount of wood treated was about one tenth of 1 percent of the t o t a l domestic production of lumber and plywood and has increased ninefold i n 20 years. How does our research stand i n rendering wood f i r e retardant? What i s the effect of fire-retardant treatments on the f i r e performance properties of wood and on the physical and mechanical properties of wood that are important to i t s u t i l i t y ? Discussion w i l l be limited to f i r e retardancy obtained by pressure impregnation, which i s currently the most effective method. F i r e retardant coatings, wood-plastic combinations, and chemical modi f i c a t i o n s of wood w i l l not be considered. Fire-Retardant Chemicals Past research on f i r e retardants, including those for wood, from about 1900 to 1968 i s reviewed i n John W. Lyons' comprehensive reference book, "The Chemistry and Uses of F i r e Retardants" (3). A more recent review by Goldstein (4) gives additional information on fire-retardant chemicals and treatment systems for wood and also discusses some of the topics of this 82

In Wood Technology: Chemical Aspects; Goldstein, Irving S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


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present paper more thoroughly. These two r e f e r e n c e s , together w i t h the o l d e r review by Browne (5) , a r e recommended t o t h e reader as b a s i c reviews on s e l e c t i o n and chemistry of f i r e r e t a r d a n t s f o r wood. The chemistry of s y n e r g i s t i c e f f e c t s between chemicals i n a f i r e - r e t a r d a n t system i s presented by Lyons ( 3 ) ; i t was a l s o d i s cussed more r e c e n t l y by Junej a (6,7) and recommended by him as an area of needed i n v e s t i g a t i o n . F i r e - r e t a r d a n t chemicals used by the commercial wood-treating i n d u s t r y a r e l i m i t e d almost e x c l u s i v e l y to mono- and diammonium phosphate, ammonium s u l f a t e , borax, b o r i c a c i d , and z i n c c h l o r i d e (4 . I t i s b e l i e v e d t h a t some use i s a l s o made of the l i q u i d ammonium polyphosphates ( 9 ) . Some a d d i t i v e s such as sodium dichrornate as a c o r r o s i o n i n h i b i t o r a r e a l s o used. Aqueous f i r e r e t a r d a n t treatment s o l u t i o n s a r e u s u a l l y formulated from two o r more of these chemicals to o b t a i n the d e s i r e d p r o p e r t i e s and c o s t advantages. For l e a c h - r e s i s t a n t type treatments, the l i t e r a t u r e shows t h a t some or a l l o f the f o l l o w i n g a r e used : urea, melamine, dicyandiamide, phosphoric a c i d , and formaldehyde (10-12). E f f e c t of F i r e - R e t a r d a n t Treatment on F i r e Performance P r o p e r t i e s What a r e t h e f i r e performance p r o p e r t i e s of untreated wood and how a r e these p r o p e r t i e s a l t e r e d by f i r e - r e t a r d a n t treatments? Ignition Wood, l i k e a l l o r g a n i c m a t e r i a l s , c h e m i c a l l y decomposes— p y r o l y z e s — w h e n subjected t o h i g h temperatures, and produces char and p y r o l y s a t e vapors or gases. When these gases escape to and from the wood s u r f a c e and a r e mixed w i t h a i r , they may i g n i t e , w i t h o r without a p i l o t flame, depending on temperature. I g n i t i o n — t h e i n i t i a t i o n of c o m b u s t i o n — i s evidenced by glowing on the wood s u r f a c e or by presence of flames above the s u r f a c e . The temperature of i g n i t i o n i s i n f l u e n c e d by many f a c t o r s r e l a t e d t o the wood under thermal exposure and the c o n d i t i o n s of i t s environment (5,13,14). F a c t o r s i n c l u d e s p e c i e s , d e n s i t y , moisture content, t h i c k n e s s and s u r f a c e a r e a , s u r f a c e absorpt i v i t y , p y r o l y s i s c h a r a c t e r i s t i c s , thermoconductivity, s p e c i f i c heat, and e x t r a c t i v e s content. Environmental c o n d i t i o n s a f f e c t i n g temperature of i g n i t i o n i n c l u d e d u r a t i o n and u n i f o r m i t y of exposure, heating r a t e , oxygen supply, a i r c i r c u l a t i o n and v e n t i l a t i o n , degree of confinement or space geometry surrounding the exposed wood element or member, temperature and c h a r a c t e r i s t i c s of an adjacent or c o n t a c t i n g m a t e r i a l , and amount of r a d i a n t energy present. Reviews c o v e r i n g i g n i t i o n of c e l l u l o s i c s o l i d s by Kanury ( 1 3 ) , B e a l l and E i c k n e r (15), Browne Ç5), and Matson e t a l . (14) r e p o r t a wide range o f i g n i t i o n temperatures obtained on wood, and dependence on r a d i a n t or c o n v e c t i v e nature of heat. For r a d i a n t



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heating of c e l l u l o s i c s o l i d s , Kanury (13) r e p o r t s spontaneous t r a n s i e n t i g n i t i o n a t a c r i t i c a l temperature of 600°C w i t h p i l o t e d t r a n s i e n t i g n i t i o n a t 300°C to 410°C. P e r s i s t e n t f l a m i n g i g n i t i o n i s r e p o r t e d a t a temperature g r e a t e r than about 320°C. With c o n v e c t i v e h e a t i n g of wood under l a b o r a t o r y c o n d i t i o n s , spontaneous i g n i t i o n i s r e p o r t e d as low as 270°C and as high as 470°C (5,14,15). Spontaneous i g n i t i o n of wood c h a r c o a l , which has e x c e l l e n t a b s o r p t i o n of oxygen and r a d i a n t heat, occurs between 150°C and 250°C ( 5 ) . I n one experiment on i g n i t i o n , oven-dried s t i c k s of n i n e d i f f e r e n t species were i g n i t e d by p i l o t flame i n 14.3 t o 40 minutes when held a t 180°C, i n 4 to 9.5 minutes when held a t 250°C and i n 0.3 to 0.5 minutes when held a t 430°C (16). Many f i e l d r e p o r t s c o l l e c t e d by U n d e r w r i t e r s L a b o r a t o r i e s , Inc. (UL) (14) show i g n i t i o n o c c u r r i n g a t or near 212°F (100°C) on wood next to steam pipes or other hot m a t e r i a l s . Laboratory experiments have not been a b l e to c o n f i r m these low i g n i t i o n tempe r a t u r e s (5,14,16,17). To p r o v i d e a margin of s a f e t y , Underw r i t e r s ' L a b o r a t o r i e s , Inc. suggests that wood not be exposed f o r long p e r i o d s of time a t temperatures g r e a t e r than 90 F (32°C) above room temperature or 170°F (77°C). The N a t i o n a l F i r e P r o t e c t i o n A s s o c i a t i o n handbook (18) g i v e s 200°C as the i g n i t i o n temperature of wood most commonly quoted, but g i v e s 66°C as the h i g h e s t temperature to which wood can be c o n t i n u a l l y exposed w i t h out r i s k of i g n i t i o n . McGuire (17) of the N a t i o n a l Research C o u n c i l of Canada suggests that 100°C would be a s a t i s f a c t o r y c h o i c e of an upper l i m i t i n g temperature f o r wood exposure. U s u a l l y the f i r e - r e t a r d a n t treatment of wood s l i g h t l y i n c r e a s e s the temperature a t which i g n i t i o n w i l l take p l a c e . There i s evidence, however, that wood t r e a t e d w i t h some chemical r e t a r d a n t s a t low r e t e n t i o n l e v e l s w i l l i g n i t e (flame) or s t a r t glowing combustion a t s l i g h t l y lower temperatures or i r r a d i a n c e l e v e l s than does untreated wood (19,20), though sustained comb u s t i o n i s u s u a l l y prevented or hindered. 1

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Thermal Degradation An e x t e n s i v e review of the l i t e r a t u r e to 1958 on thermal degradation of wood i s g i v e n by Browne ( 5 ) . B e a l l and E i c k n e r (15) and G o l d s t e i n (4) add a d d i t i o n a l review i n f o r m a t i o n on t h i s complex s u b j e c t . S h a f i z a d e h s (21) review of the p y r o l y s i s and combustion chemistry of c e l l u l o s e g i v e s a b a s i s f o r understanding these processes i n wood and the e f f e c t of f i r e - r e t a r d a n t treatment on these processes. Browne (5) d e s c r i b e d the p y r o l y s i s r e a c t i o n s and events which occur i n each of four temperature zones or ranges when s o l i d wood of a p p r e c i a b l e t h i c k n e s s i s exposed to heat i n absence of a i r . Zone A i s below 200°C; Zone B, 200° to 280°C; Zone C, 280° t o 500°C; and Zone D, above 500°C. These zones may be present s i m u l taneously. When wood i s heated i n a i r , events o c c u r r i n g i n these 1



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temperature zones i n c l u d e o x i d a t i o n r e a c t i o n s and, a f t e r i g n i t i o n , combustion of the p y r o l y s i s and o x i d a t i o n products. G o l d s t e i n (4) more simply d i v i d e d the thermal degradation processes i n t o those o c c u r r i n g a t low temperatures, below 200°C, and those a t h i g h temperatures, above 200°C. Decomposition of wood exposed to temperatures below 200°C i s slow but measurable (22,23). For example, the average l o s s i n weight of 11 s p e c i e s of wood was 2.7 percent i n 1 year a t 93°C and 21.4 percent i n 102 hours a t 167°C (22). Sound wood w i l l not g e n e r a l l y i g n i t e below 200°C s i n c e products evolved a r e mostly carbon d i o x i d e and water vapor. High temperature degradation processes above 200°C i n c l u d e r a p i d p y r o l y s i s of the wood components, combustion o f flammable gases and t a r s , glowing of the char r e s i d u e , and e v o l u t i o n of unburned gases, vapors, and smoke. The most w i d e l y accepted theory of the mechanism of f i r e r e t a r d a n t chemicals i n reducing flaming combustion of wood i s that the chemicals a l t e r the p y r o l y s i s r e a c t i o n s w i t h formation of l e s s flammable gases and t a r s and more char and water (4,5,8,21,24-29). Some f i r e r e t a r d a n t s s t a r t and end the chemical decomposition a t lower temperatures. Heat of combustion of the v o l a t i l e s i s r e duced. Shafizadeh (21) suggests that a primary f u n c t i o n of f i r e r e t a r d a n t s i s to promote dehydration and c h a r r i n g of c e l l u l o s e . The normal degradation of c e l l u l o s e to the flammable t a r , levoglucosan, i s reduced and the c h a r r i n g of t h i s compound i s promoted. Shafizadeh and coworkers used thermogravimetric (TG) and thermal e v o l u t i o n a n a l y s i s (TEA) data, to conf irm two d i f f e r e n t mechanisms i n v o l v e d i n flameproofing c e l l u l o s i c m a t e r i a l s : 1) d i r e c t i n g the p y r o l y s i s r e a c t i o n s to produce char, water, and carbon d i o x i d e i n p l a c e of flammable v o l a t i l e s , and 2) p r e v e n t i n g the f l a m i n g combustion of these v o l a t i l e s ( 2 7 ) . F i r e Penetration The property of a wood m a t e r i a l or assembly t o r e s i s t the p e n e t r a t i o n of f i r e or to continue to perform a g i v e n s t r u c t u r a l f u n c t i o n , or both, i s commonly termed f i r e r e s i s t a n c e . The measure of elapsed time that a m a t e r i a l or assembly w i l l e x h i b i t f i r e r e s i s t a n c e under the s p e c i f i e d c o n d i t i o n s of t e s t and performance i s c a l l e d f i r e endurance. Large furnaces a r e used t o measure f i r e endurance of w a l l s , f l o o r s , r o o f s , doors, columns, and beams under the standard ASTM E119 (30) time-temperature exposure c o n d i t i o n s . Wood has e x c e l l e n t n a t u r a l r e s i s t a n c e to f i r e p e n e t r a t i o n due to i t s low thermal c o n d u c t i v i t y and to the c h a r a c t e r i s t i c of forming an i n s u l a t i n g l a y e r of c h a r c o a l w h i l e burning. The wood beneath the char s t i l l r e t a i n s most of i t s o r i g i n a l s t r e n g t h properties. In wood c h a r r i n g s t u d i e s by S c h a f f e r a t the F o r e s t Products Laboratory (FPL) (31), 3 - i n c h - t h i c k p i e c e s of wood were v e r t i c a l l y


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exposed to f i r e on one s u r f a c e . Rate of char development a t three constant f i r e exposure temperatures, 1,000°F (538°C) 1,500°F (816 C), and 1,700°F (927°C), was described by an equation w i t h an Arrhenius temperature-dependent r a t e constant. When specimens were exposed to the uniformly i n c r e a s i n g f i r e temperatures of ASTM E119 ( e a r l i e r l i n e a r p o r t i o n of timetemperature curve) (30), the r a t e of char development was constant, a f t e r the more r a p i d l y developed f i r s t 1/4 i n c h o f char. Under the standard ASTM f i r e exposure, temperatures 1/4 i n c h from the specimen s u r f a c e reached 1,400°F (760°C) a t 15 minutes, 1,700°F (927 C) a t 1 hour, and 1,850°F (1,010°C) a t 2 hours (31). When wood i s exposed to these c o n d i t i o n s , the f i r s t v i s u a l e f f e c t of thermal degradation (Figure 1) i s i n d i c a t e d by browning of the wood a t about 350°F to 400°F (175°C to 200 C). The temperature which c h a r a c t e r i z e d the base of the char l a y e r was 550°F (288°C). A f t e r the f i r s t 1/4 i n c h of char development, the r a t e that t h i s char l a y e r moved i n t o the s o l i d wood—the r a t e o f f i r e penet r a t i o n — w a s about 38 m i l l i m e t e r s per hour (1-1/2 i n / h r ) . Schaffer (31) found some d i f f e r e n c e s i n char development r a t e i n the three species s t u d i e d , D o u g l a s - f i r , southern pine, and white oak. Charring r a t e decreased w i t h i n c r e a s e i n dry s p e c i f i c g r a v i t y and w i t h i n c r e a s e i n moisture content. He a l s o found that growth-ring o r i e n t a t i o n p a r a l l e l to the exposed f a c e r e s u l t e d i n higher c h a r r i n g r a t e s than when o r i e n t a t i o n was perpendicular to the exposed f a c e . I n s t u d i e s a t the J o i n t F i r e Research Organi z a t i o n i n Great B r i t a i n (32) on r a t e of burning, increased p e r m e a b i l i t y along the g r a i n was found to i n c r e a s e r a t e of char. S c h a f f e r (33) found that impregnations of southern pine w i t h c e r t a i n f i r e - r e t a r d a n t and other chemicals d i d not s i g n i f i c a n t l y change the r a t e of c h a r r i n g . B o r i c a c i d , borax, ammonium s u l f a t e , monosodium phosphate, potassium carbonate, and sodium hydroxide v a r i o u s l y reduced the r a t e of c h a r r i n g a f t e r 20 minutes of f i r e exposure by about 20 percent over untreated wood. Only p o l y ethylene g l y c o l 1,000 reduced the r a t e of c h a r r i n g over the e n t i r e period of f i r e exposure by about 25 percent over untreated wood. T e t r a k i s (hydroxymethyl) phosphonium c h l o r i d e with urea, d i c y andiamide w i t h phosphoric a c i d , monoammonium phosphate, z i n c c h l o r i d e , and sodium c h l o r i d e had no e f f e c t on c h a r r i n g r a t e . Commercial f i r e-r etardant treatments g e n e r a l l y do not add s i g n i f i c a n t l y to the f i r e endurance of assemblies. I t i s o f t e n more advantageous from the cost standpoint, e i t h e r to use t h i c k e r wood members or to s e l e c t species w i t h lower c h a r r i n g r a t e s , than to add the cost of the f i r e - r e t a r d a n t treatment. In some a s semblies, however, i t has been found worthwhile to use some f i r e r e t a r d a n t - t r e a t e d components i n order to g a i n the extra time which w i l l b r i n g the f i r e endurance time up to the g o a l d e s i r e d . For example, t r e a t e d wood studs i n w a l l s and treated r a i l s , s t i l e s , and cross bands i n s o l i d wood doors have been used.


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Flame Spread In the ASTM E84 25-foot t u n n e l furnace t e s t (34) f o r measuring flame spread of b u i l d i n g m a t e r i a l s , an i g n i t i n g p i l o t flame i s a p p l i e d to the underside of a h o r i z o n t a l l y mounted specimen. The flame heats the combustible m a t e r i a l to p y r o l y s i s , and the flammable gases g i v e n o f f a r e i g n i t e d by the p i l o t flame. I f the p y r o l y s i s - c o m b u s t i o n process becomes exothermic, the flaming on the specimen becomes s e l f - p r o p a g a t i n g . A flame-spread c l a s s i f i c a t i o n or r a t i n g number i s c a l c u l a t e d from the timed i s t a n c e progress of the flame along the l e n g t h of the specimen surface. The flame-spread number i s d e r i v e d r e l a t i v e to red oak (with an a r b i t r a r y flame-spread r a t i n g of 100) and to asbestos-cement board (rated zero)· N a t u r a l wood products ( 1 - i n c h lumber) u s u a l l y have flame-spread r a t i n g s of 100 to 150 i n the t e s t furnace of U n d e r w r i t e r s L a b o r a t o r i e s , Inc. (35). Some exceptions are poplar (170-185), western hemlock (60-75), redwood (70), and n o r t h e r n spruce (65). Wood w e l l t r e a t e d w i t h c u r r e n t commercial f i r e - r e t a r d a n t impregnation treatments w i l l have flame-spread r a t i n g s of 25 or l e s s . Many t r e a t e d wood products have obtained a s p e c i a l marking or d e s i g n a t i o n "FR-S" from UL (36) f o r having a flame-spread, f u e l c o n t r i b u t e d , and smoke-developed c l a s s i f i c a t i o n of not over 25 and no evidence of s i g n i f i c a n t p r o g r e s s i v e combustion i n an extended 30-minute ASTM E84 (34) t e s t procedure. The f u e l - c o n t r i b u t e d and smoke-developed c l a s s i f i c a t i o n s are a l s o c a l c u l a t e d r e l a t i v e to performance of red oak and asbestos-cement board. Eickner and S c h a f f e r (10) found t h a t monoammonium phosphate ( F i g u r e 2) was the most e f f e c t i v e of d i f f e r e n t f i r e - r e t a r d a n t chemicals i n reducing the flame-spread index of D o u g l a s - f i r plywood. They used the 8-foot t u n n e l furnace of ASTM E286 (37). The untreated plywood had a flame-spread index of 115. This was reduced to about 55 at a chemical r e t e n t i o n of 2 pounds per c u b i c f o o t , to 35 at 3 pounds, 20 a t 4 pounds, and to about 15 a t r e t e n t i o n s of 4.5 pounds and h i g h e r . Zinc c h l o r i d e was next i n e f f e c t i v e n e s s but r e q u i r e d higher r e t e n t i o n l e v e l s to reduce the flame-spread index v a l u e s e q u i v a l e n t to monoammonium phosphate. I t r e q u i r e d 5.5 pounds of z i n c c h l o r i d e to reduce flame spread to 35, and 7 pounds to reduce flame spread to 25. Ammonium s u l f a t e and borates were as e f f e c t i v e as z i n c c h l o r i d e a t r e t e n t i o n s of about 4.5 pounds per c u b i c f o o t and lower but not as e f f e c t i v e a t higher r e t e n t i o n l e v e l s . B o r i c a c i d had some e f f e c t i v e n e s s i n reducing flame spread. I t was e q u i v a l e n t to z i n c c h l o r i d e , ammonium s u l f a t e , and the borates at a r e t e n t i o n of about 2 pounds per c u b i c f o o t , but much l e s s e f f e c t i v e a t h i g h r e t e n t i o n l e v e l s . A r e t e n t i o n of 6 pounds per c u b i c f o o t reduced the flame-spread index of the plywood to o n l y 60. In many l a b o r a t o r i e s , flame-spread t e s t s of d i f f e r e n t types have c o n s i s t e n t l y shown t h a t the c u r r e n t acceptable treatments w i l l 1



WOOD TECHNOLOGY:

C H E M I C A L ASPECTS

Figure 1. Fire penetration into wood and formation of char hyer under the fire exposure conditions of ASTM E119 120

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Figure 2. Relationship of flame spread to level of chemical reten tion in 3/8-in. Douglas-fir plywood evaluated by the 8-ft tunnel furnace method


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p r e v e n t f l a m i n g c o m b u s t i o n o f t h e wood a n d p r e v e n t s p r e a d o f f i r e over the s u r f a c e . Wood, p r o p e r l y t r e a t e d , w i l l b e s e l f e x t i n g u i s h i n g o f b o t h f l a m i n g and g l o w i n g o n c e t h e p r i m a r y s o u r c e o f h e a t a n d f i r e i s removed o r e x h a u s t e d .


Glowing Glowing i s the v i s u a l evidence of combustion of the carbon i n t h e c h a r l a y e r o f t h e b u r n i n g wood. I f flaming of the released combustible gases has ceased, the glowing of the char i s u s u a l l y termed a f t e r g l o w . Of t h e s e v e r a l p o s s i b l e o x i d a t i o n r e a c t i o n s i n g l o w i n g c o m b u s t i o n , b o t h Browne (5) and L y o n s (3) i n t h e i r r e v i e w s show one p o s s i b i l i t y t o be a t w o - s t a g e r e a c t i o n : (1)

C + %0

(2)

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CO + 2 6 . 4 3 k i l o c a l o r i e s p e r m o l e

2

2

·+ C 0

2

+ 67.96 k i l o c a l o r i e s p e r mole

The f i r s t r e a c t i o n o c c u r s o n t h e s u r f a c e o f t h e char and t h e second i s a g a s - p h a s e r e a c t i o n . Wood t h a t h a s b e e n e f f e c t i v e l y t r e a t e d s h o u l d n o t e x h i b i t a n y afterglowing. Reviews C3,5) c o v e r i n g t h e s u b j e c t o f g l o w i n g p o i n t out t h a t t h e mechanism i n v o l v e d i n glow r e t a r d a n c e i s n o t c l e a r . B o t h p h y s i c a l and c h e m i c a l t h e o r i e s have been s u g g e s t e d . Physical methods i n c l u d e t h e e x c l u s i o n o f oxygen from t h e carbonaceous char by f o r m a t i o n o f c o a t i n g s o f t h e f i r e r e t a r d a n t d u r i n g t h e comb u s t i o n p r o c e s s o r by a c o o l i n g e f f e c t due to t h e f i r e r e t a r d a n t . The c h e m i c a l t h e o r y w i t h t h e most s u p p o r t i n g e v i d e n c e i n d i c a t e s t h a t e f f e c t i v e g l o w r e t a r d a n c e i n c r e a s e s t h e r a t i o o f CO t o C 0 . 2

I f t h e r e a c t i o n c a n b e d i r e c t e d m o s t l y t o t h e m o n o x i d e , s t e p (1) a b o v e , t h e h e a t l i b e r a t e d i s o n l y 28 p e r c e n t o f t h a t g i v e n o f f when the r e a c t i o n continues to the d i o x i d e . Thus g l o w i n g may b e e l i m i n a t e d b y a n i n s u f f i c i e n t amount o f h e a t t o c o n t i n u e combustion. E f f e c t i v e g l o w r e t a r d a n t s f o r wood a r e t h e ammonium p h o s p h a t e s , ammonium b o r a t e s , b o r i c a c i d , p h o s p h o r i c a c i d , a n d compounds t h a t y i e l d p h o s p h o r i c a c i d d u r i n g p y r o l y s i s 0 3 , 5 ) . Some c h e m i c a l s t h a t a r e r e p o r t e d t o s t i m u l a t e g l o w i n g a r e chromâtes, m o l y b d a t e s , h a l i d e s o f chromium, manganese, c o b a l t and c o p p e r , a n d f e r r i c and s t a n n i c o x i d e s ( 5 , 1 0 ) . Chemicals found to be i n e f f e c t i v e i n r e t a r d i n g a f t e r g l o w i n a l i m i t e d s t u d y were ammonium s u l f a t e and s o d i u m b o r a t e s (10). Combustion Products T h e c o m b u s t i o n p r o d u c t s o f b u r n i n g wood—smoke a n d g a s e s — a r e becoming o f i n c r e a s e d Importance. Code and b u i l d i n g o f f i c i a l s , b u i l d e r s , p r o d u c e r s o f b u i l d i n g m a t e r i a l s and f u r n i s h i n g s , and a l l



90

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

engaged i n f i r e r e s e a r c h are being d i r e c t e d by p u b l i c i n t e r e s t and s c r u t i n y toward a g r e a t e r concern f o r the r e a l hazard to l i f e s a f e t y of b u i l d i n g m a t e r i a l s i n a f i r e s i t u a t i o n . A study conducted by the N a t i o n a l F i r e P r o t e c t i o n A s s o c i a t i o n (18) of 311 f a t a l f i r e s i n one- and two-family d w e l l i n g s , i n c l u d i n g mobile homes and r e c r e a t i o n a l v e h i c l e s , r e v e a l e d that 73.6 percent of the deaths were caused by products of combustion r e s u l t i n g i n a s p h y x i a t i o n or a n o x i a . I n a study of f i r e f a t a l i t i e s that occurred i n the s t a t e of Maryland, a Johns Hopkins U n i v e r s i t y group (38) found that carbon monoxide was not o n l y the predominant f a c t o r i n h i n d e r i n g escape from the f i r e scene but was a l s o the primary agent i n the cause of death i n 50 percent of the 129 cases. I t was a l s o a major c o n t r i b u t o r to death i n another 30 percent of the cases i n combination w i t h heart d i s e a s e , a l c o h o l i n the b l o o d , and burns. V i s i b i l i t y i n a burning b u i l d i n g i s extremely important. Smoke can obscure v i s i o n and e x i t s , thereby r e t a r d i n g escape and r e s u l t i n g i n p a n i c . I t a l s o h i n d e r s the work of f i r e f i g h t e r s . The p a r t i c u l a r f r a c t i o n of smoke, e x c l u s i v e of any combustion gases, a c t s as an i r r i t a n t to the r e s p i r a t o r y system and may a l s o r e s u l t i n hypoxia and c o l l a p s e (39). Smoke from untreated wood.—For r e s e a r c h purposes, t h e r e a r e s e v e r a l methods used f o r measuring smoke developed by burning b u i l d i n g m a t e r i a l s (40). These t e s t s g e n e r a l l y measure the v i s i b l e smoke products. One method of smoke d e t e r m i n a t i o n being used f o r b u i l d i n g code purposes i s the 25-foot t u n n e l furnace method of ASTM E84 which y i e l d s a smoke-developed r a t i n g r e l a t i v e to red oak. Because the t e s t i s conducted under a s t r o n g flame, the r e s u l t s are not always i n d i c a t i v e of performance i n a b u i l d i n g f i r e where m a t e r i a l s may have some high-temperature exposure without the presence of flames. During the l a s t decade, the N a t i o n a l Bureau of Standards (NBS) and other l a b o r a t o r i e s worked to develop a meaningful t e s t method f o r measuring the smoke development p o t e n t i a l of burning wood and other b u i l d i n g m a t e r i a l s . The method developed a t NBS i s now e x t e n s i v e l y used (41,42). This method t h e r m a l l y exposes a s m a l l sample i n a closed chamber and s u p p l i e s a s p e c i f i c o p t i c a l d e n s i t y based on l i g h t t r a n s m i s s i o n , l i g h t path l e n g t h , burning a r e a , and volume of e n c l o s u r e . I t i s intended to r e l a t e to l i g h t o b s c u r a t i o n and the hindrance i n f i n d i n g e x i t s . This method has been accepted as a standard by the N a t i o n a l F i r e P r o t e c t i o n A s s o c i a t i o n (43) and i s expected to be accepted by others and more w i d e l y used f o r r a t i n g b u i l d i n g m a t e r i a l s f o r r e g u l a t o r y purposes. The chemical makeup of the combustion products, i n c l u d i n g a e r o s o l s and p a r t i c u l a t e s , w i l l change w i t h burning c o n d i t i o n s and the complex processes r e s u l t i n complex mixtures of products (28). More smoke i s produced under nonflaming combustion than under flaming combustion. The complexity of the smoke i s i n d i c a t e d by the f a c t that over 200 compounds have been found i n the d e s t r u c t i v e d i s t i l l a t i o n of wood by Goos (45).



6.

HOLMES

Fire-Retardant

Treatment

91

In complete combustion, the products from burning wood a r e carbon d i o x i d e , water, and ash. Other gases and vapors that may be present due to incomplete combustion i n c l u d e carbon monoxide, methane, formic a c i d , a c e t i c a c i d , g l y o x a l , and saturated and unsaturated hydrocarbons (46) . The a e r o s o l s can a l s o c o n t a i n v a r i o u s l i q u i d s such as levoglucosan and complex mixtures. The s o l i d s can c o n s i s t of unburned carbon p a r t i c l e s and high-molecularweight t a r s . There i s no standardized t e s t method f o r determining the combustion products g i v e n o f f from wood or other m a t e r i a l s dur ing a r e a l f i r e s i t u a t i o n . The gases and products obtained and t h e i r estimated hazard to l i f e w i l l depend on the experimental cond i t i o n s of any t e s t method s e l e c t e d . Most s t u d i e s on the t o x i c i t y of combustion products show that the dominant hazardous gas from burning wood i s carbon monoxide f o l l o w e d by carbon d i o x i d e and the r e s u l t i n g oxygen d e p l e t i o n (46-50). Considerable r e s e a r c h i s underway by v a r i o u s i n s t i t u t i o n s and agencies and by i n d u s t r y on the p h y s i o l o g i c a l and t o x i c o l o g i c a l e f f e c t s of smoke and gaseous products. Of p a r t i c u l a r note are the e x t e n s i v e r e s e a r c h programs at the U n i v e r s i t y of Utah under the d i r e c t i o n on I . N. Einhorn (44,48), at Johns Hopkins Unive r s i t y under R. M. F r i s t r o m (38,50), and a t the N a t i o n a l Bureau of Standards under M. M. B i r k y ( 5 1 ) . Smoke from t r e a t e d w o o d . — F i r e - r e t a r d a n t - t r e a t e d wood a l s o produces smoke and gaseous combustion products when burned. Many commercial f i r e - r e t a r d a n t - t r e a t e d wood products showed g r e a t l y reduced smoke development when t e s t e d i n the 25-foot tunnel furnace used f o r r a t i n g purposes by UL (36). This t e s t , however, does i n v o l v e flaming exposure, r e g a r d l e s s of the f l a m m a b i l i t y of the specimen. I n a recent study a t the FPL (52), r e s u l t s of t e s t s w i t h the NBS smoke chamber show that plywood t r e a t e d w i t h s p e c i f i c f i r e - r e t a r d a n t chemicals may g i v e o f f more or l e s s smoke than untreated wood depending on the chemicals employed and t h e c o n d i t i o n s of burning. Eickner and Schaffer (10) examined the e f f e c t s of v a r i o u s i n d i v i d u a l f i r e - r e t a r d a n t chemicals on f i r e performance of D o u g l a s - f i r plywood ( F i g u r e 3 ) . Using the 8-foot tunnel furnace t e s t method (37), they found that monoammonium phosphate and z i n c c h l o r i d e g r e a t l y increased the smoke d e n s i t y index v a l u e s f o r the plywood when treatment l e v e l s were above 2.0 pounds per c u b i c f o o t . B o r i c a c i d , a t r e t e n t i o n s above 5 pounds per cubic f o o t , a l s o increased smoke development. Sodium borates and sodium dichrornate c o n s i d e r a b l y reduced smoke development. A t low r e t e n t i o n l e v e l s of about 1 to 3-1/2 pounds per cubic f o o t , ammonium s u l f a t e was a l s o found e f f e c t i v e i n reducing smoke. I n the 8-foot furnace, e f f e c t i v e f i r e r e t a r d a n t s produced a lowflaming combustion and t h i s c o n d i t i o n g e n e r a l l y r e s u l t e d i n more smoke development than i n the flaming combustion of untreated wood.



WOOD TECHNOLOGY:

DRY

CHEMICAL

RETENTION

(POUNDS

C H E M I C A L ASPECTS

PER CUBIC FOOT)

Figure 3. Relationship of smoke density to level of chemical retention in 3/8-in. Douglas-fir plywood evaluated by the 8-ft tunnel furnace method



6.

HOLMES

Fire-Retardant

Treatment

93

Satonaka and I t o (53) obtained reduced smoke from f i r and oak t r e a t e d w i t h e i t h e r ammonium s u l f a t e or diammonium phosphate, or w i t h the commercially used f o r m u l a t i o n s p y r e s o t e or m i n a l i t h . (Pyresote c o n s i s t s of z i n c c h l o r i d e 35 p e r c e n t , ammonium s u l f a t e 35 percent, b o r i c a c i d 25 p e r c e n t , and sodium dichromate 5 percent. M i n a l i t h c o n s i s t s of ammonium s u l f a t e 60 percent, diammonium phosphate 10 p e r c e n t , b o r i c a c i d 20 p e r c e n t , and borax 10 percent.) They a l s o obtained r e d u c t i o n s i n carbon monoxide and carbon d i o x i d e l e v e l s compared to the untreated wood w i t h each of the four treatments at the two p y r o l y s i s temperatures employed, 400°C and 700°C. The p o s s i b i l i t y of t o x i c gas f o r m a t i o n can o c c a s i o n a l l y be p r e d i c t e d from the chemical composition of f i r e - r e t a r d a n t f o r m u l a t i o n s . Chemicals c o n t a i n i n g c h l o r i n e may produce c h l o r i n e gas, hydrogen c h l o r i d e , or other c h l o r i n a t e d products. Ammonia gas may a l s o be a noxious gas from ammonia-containing compounds. The trend i n r e c e n t years has been toward increased i n v e s t i g a t i o n and use of o r g a n i c compounds as f i r e r e t a r d a n t s f o r wood. The thermal decomposition products from wood t r e a t e d w i t h these compounds i s not c l e a r l y understood, p a r t i c u l a r l y i n regard to t h e i r t o x i c o l o g i c a l and p h y s i o l o g i c a l e f f e c t s . I n f o r m a t i o n on r e s e a r c h i n t h i s area i s l a c k i n g . Heat C o n t r i b u t i o n At some time a f t e r the i n i t i a l exposure of wood to heat and flames i n a f i r e s i t u a t i o n , the burning process becomes exothermic and heat i s c o n t r i b u t e d to the surroundings. The t o t a l heat of combustion of wood v a r i e s w i t h species and i s a f f e c t e d by r e s i n content. I t v a r i e s from about 7,000 to 9,000 Btu per pound, but not a l l of t h i s p o t e n t i a l heat i s r e l e a s e d during a f i r e . The degree to which the t o t a l a v a i l a b l e heat i s r e l e a s e d depends on the type of f i r e exposure and the completeness of combustion. During the i n i t i a l stages of a f i r e , f i r e - r e t a r d a n t - t r e a t e d wood c o n t r i b u t e s l e s s heat than does untreated wood, e s p e c i a l l y from the flammable v o l a t i l e s (8,26). This means that the spread of f i r e to nearby combustibles i s slow. The f i r e tends to be confined to the primary source. I n the ASTM E84 t e s t f o r b u i l d i n g m a t e r i a l s , t r e a t e d specimens produce about 75 percent l e s s heat than untreated red oak. I n a t o t a l combustion t e s t , however, such as the N a t i o n a l Bureau of Standards " p o t e n t i a l heat method (54), both t r e a t e d and untreated wood r e l e a s e about the same t o t a l heat. Heat r e l e a s e r a t e i s another r e l e v a n t measure of the c o m b u s t i b i l i t y of a m a t e r i a l along w i t h ease of i g n i t i o n and flame spread. Smith (55) p o i n t s out that the r e l e a s e r a t e d a t a , obtained under d i f f e r e n t t e s t exposures, w i l l be u s e f u l i n p r e d i c t i n g the performance i n a c t u a l f i r e s under d i f f e r e n t f u e l l o a d i n g . Release r a t e data can thus be u s e d — a l o n g w i t h other 11



94

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

f i r e performance c h a r a c t e r i s t i c s — f o r s p e c i f y i n g m a t e r i a l s and products i n a p a r t i c u l a r l o c a t i o n i n an occupancy w i t h a given f u e l load r a t i n g . The r a t e of heat r e l e a s e during the i n i t i a l stages of f i r e exposure i s c o n s i d e r a b l y l e s s , however, f o r t r e a t e d wood than f o r untreated wood. Brenden (56), using the FPL r a t e of heat r e l e a s e method, obtained a maximum heat r e l e a s e r a t e of 611 Btu per square f o o t per minute f o r untreated 3/4-inch D o u g l a s - f i r plywood, w i t h an average r e l e a s e r a t e of 308 B t u per square f o o t per minute f o r the f i r s t 10 minutes. F i r e - r e t a r d a n t - t r e a t e d D o u g l a s - f i r plywood, w i t h 3.6 pounds per cubic f o o t d r y chemical and a r e ported flame spread of 25 to 28, had a maximum heat r e l e a s e r a t e of 132 B t u per square f o o t per minute a t 42 minutes and an average r a t e of 16 Btu per square f o o t per minute f o r the f i r s t 10 minutes. Treatment-Related P r o p e r t i e s of Fire-Retardant-Treated Wood Strength Gerhards (57) reviewed the r e s u l t s of 12 separate s t u d i e s on s t r e n g t h p r o p e r t i e s of f i r e - r e t a r d a n t - t r e a t e d wood conducted a t the FPL and other l a b o r a t o r i e s . He concluded that modulus of rupture (MOR) i s c o n s i s t e n t l y lower and modulus of e l a s t i c i t y (MOE) and work to maximum load a r e g e n e r a l l y lower f o r f i r e r e t a r d a n t - t r e a t e d wood than f o r untreated wood i f f i r e - r e t a r d a n t treatment i s followed by k i l n d r y i n g . The e f f e c t may be l e s s or n e g l i g i b l e i f the f i r e - r e t a r d a n t - t r e a t e d wood i s a i r d r i e d i n s t e a d of k i l n d r i e d . The most s i g n i f i c a n t l o s s was i n work to maximum l o a d , a measure of shock r e s i s t a n c e or brashness, which averaged 34 percent r e d u c t i o n . The l o s s e s from t r e a t i n g and k i l n drying f o r s m a l l c l e a r specimens averaged about 13 percent f o r MOR and 5 percent f o r MOE. Losses i n s t r u c t u r a l s i z e s were about 14 percent f o r MOR and 1 percent f o r MOE (57). Losses due to h i g h temperature k i l n d r y i n g , above 65°C may be c o n s i d e r a b l y greater ( 5 8 ) . The N a t i o n a l Forest Products A s s o c i a t i o n recommends that t h e a l l o w a b l e s t r e s s e s f o r f i r e - r e t a r d a n t - t r e a t e d wood f o r design purposes be reduced by 10 percent as compared to untreated wood; the a l l o w a b l e loads f o r f a s t e n e r s a r e a l s o reduced 10 percent ( 5 9 ) . The 10 percent r e d u c t i o n i n design s t r e s s e s was confirmed prov i d i n g the s w e l l i n g of the wood r e s u l t i n g from treatment i s taken i n t o account (57,60). Treated wood i s s l i g h t l y more hygroscopic than untreated, t h e r e f o r e the d e n s i t y of e q u i v a l e n t cross s e c t i o n s of the t r e a t e d t e s t samples was s l i g h t l y lower. B r a z i e r and Laidlaw (58) a t the P r i n c e s Risborough Laboratory have w r i t t e n t h a t , u n t i l more research i s done i n t h i s area, i t i s wise t o assume a l o s s i n bending s t r e n g t h of 15 to 20 percent f o r t r e a t e d wood d r i e d a t 65°C.



6.

HOLMES

Fire-Retardant

Treatment

95

In a d d i t i o n t o s t r e n g t h l o s s due to k i l n d r y i n g a t h i g h temperatures (above 65°C), p r o g r e s s i v e l o s s of s t r e n g t h i n t r e a t e d wood members can be caused by a c i d i c degradation of the wood by some treatment chemicals (58). There i s evidence t h a t phosphate and s u l f a t e s a l t s may be broken down t o a c i d i c r e s i d u e s w i t h i n the wood. The degradation and r e s u l t a n t l o s s i n s t r e n g t h may continue at a slower r a t e under use a t normal temperatures. The f i r e - r e t a r d a n t treatment of l a r g e s t r u c t u r a l members f o r a p p l i c a t i o n s where s t r e n g t h i s a predominant f a c t o r i s u s u a l l y not recommended. The adverse e f f e c t s of treatment chemicals on s t r e n g t h and other p r o p e r t i e s such as h y g r o s c o p i c i t y outweigh any b e n e f i t obtained by the treatment. Large wood members have good f i r e r e s i s t a n c e and i f treatment i s r e q u i r e d f o r reducing flame spread, i t would be b e t t e r to use f i r e - r e t a r d a n t c o a t i n g s or other protection. Hygroscopicity Wood t h a t has not been t r e a t e d w i l l absorb moisture from the surrounding a i r u n t i l i t s moisture content reaches an e q u i l i b r i u m c o n d i t i o n . The h y g r o s c o p i c i t y of wood t r e a t e d w i t h i n o r g a n i c f i r e r e t a r d a n t chemicals i s u s u a l l y g r e a t e r than that of the untreated wood and i s dependent on s i z e and species of wood, temperature, r e l a t i v e humidity, and type and amount of chemicals used (8,60). The i n c r e a s e i n e q u i l i b r i u m moisture content i s n e g l i g i b l e a t 27°C and 30 to 50 percent r e l a t i v e humidity. A 2 to 8 percent i n c r e a s e i n moisture content occurs i n the t r e a t e d wood a t 27°C and 65 percent r e l a t i v e humidity, and a t 80 percent r e l a t i v e humidity the moisture content may i n c r e a s e 5 to 15 percent and cause exudation of the chemical s o l u t i o n from the wood. In an unpublished study a t the U.S. F o r e s t Products Labo r a t o r y , the moisture content of wood t r e a t e d w i t h two commercial f o r m u l a t i o n s reached 48 to 58 percent (based on ovendry weight of t r e a t e d sample) i n 4 weeks exposure a t 27°C and 90 percent r e l a t i v e humidity. Continuous exposure of wood t r e a t e d w i t h waters o l u b l e s a l t s to c o n d i t i o n s above 80 percent r e l a t i v e humidity can r e s u l t i n l o s s of chemicals and i n adverse e f f e c t s on dimensional s t a b i l i t y and p a i n t c o a t i n g s . C o r r o s i o n of some metals i n contact w i t h the wood w i l l a l s o occur. Zinc c h l o r i d e w i l l add c o n s i d e r a b l y t o the e q u i l i b r i u m moisture content of wood i n the range of 30 to 80 percent r e l a t i v e humidity ( 8 ) . Ammonium s u l f a t e w i l l add a t r e l a t i v e h u m i d i t i e s exceeding 65 percent, and borax and b o r i c a c i d w i l l a t t r a c t water at lower h u m i d i t i e s . Phosphate s a l t s a f f e c t h y g r o s c o p i c i t y mostly when r e l a t i v e humidity exceeds 80 percent ( 5 8 ) . Most commercial treatment f o r m u l a t i o n s a r e developed f o r use under c o n d i t i o n s not g r e a t e r than 80 percent r e l a t i v e humidity. An e x t e r i o r type, l e a c h - r e s i s t a n t treatment t h a t i s not hygroscopic i s a v a i l a b l e (61). 1


96

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS


Gluing G e n e r a l l y , the bonding o b t a i n a b l e w i t h f i r e - r e t a r d a n t - t r e a t e d wood i s s a t i s f a c t o r y f o r d e c o r a t i v e purposes. Treated wood members can be bonded i n t o s t r u c t u r a l assemblies w i t h s p e c i a l l y formulated adhesives under optimum bonding c o n d i t i o n s ( 8 ) . However, the q u a l i t y of bonds i s not u s u a l l y equal to that o b t a i n a b l e w i t h untreated wood, p a r t i c u l a r l y i n e v a l u a t i o n a f t e r exposure t o c y c l i c wetting and d r y i n g ( 6 2 ) . Corrosivity Current treatment s o l u t i o n s c o n t a i n i n g c o r r o s i v e i n o r g a n i c s a l t s u s u a l l y a l s o c o n t a i n c o r r o s i o n i n h i b i t o r s such as sodium dichromate o r ammonium thiocyanate or a r e formulated t o a more n e u t r a l pH (60). However, s o l u b l e - s a l t - t r e a t e d wood i n contact w i t h metals should not be exposed t o high r e l a t i v e h u m i d i t i e s f o r prolonged p e r i o d s . The treatment chemicals can a t t a c k and det e r i o r a t e metal f a s t e n e r s . The c o r r o s i o n products i n t u r n d e t e r i o r a t e the wood. For example, under humid c o n d i t i o n s , ammonium s u l f a t e w i l l a t t a c k the z i n c and i r o n of galvanized punched-steel n a i l p l a t e s used i n t r u s s e s (58). A l k a l i n e and a c i d i c areas a r e developed i n the wood next to the attacked metal f a s t e n e r , and cause degradation of the wood (58,63). Paintability P a i n t a b i l i t y i s g e n e r a l l y not a problem under d r y normal c o n d i t i o n s . Unusually h i g h r e l a t i v e humidity c o n d i t i o n s can a f f e c t adhesion of the p a i n t f i l m or cause chemical c r y s t a l blooming on the p a i n t surface due to the increased moisture content of the wood. N a t u r a l or c l e a r f i n i s h e s a r e g e n e r a l l y not used f o r t r e a t e d wood because the chemicals may cause darkening or i r r e g u l a r s t a i n i n g . Machining The a b r a s i v e e f f e c t of treatments w i t h i n o r g a n i c s a l t c r y s t a l s can reduce t o o l l i f e . Where machining i s necessary, t h i s can be minimized by u s i n g t o o l s of abra s i v e-r es i s tant a l l o y s . Durability F i r e - r e t a r d a n t - t r e a t e d wood i s durable and s t a b l e under normal exposure c o n d i t i o n s . Treatments using i n o r g a n i c waters o l u b l e s a l t s , however, a r e not recommended f o r e x t e r i o r exposures to r a i n and weathering unless the treatment can be adequately protected by w a t e r - r e p e l l e n t c o a t i n g . E x t e r i o r - t y p e treatments i n which the chemicals a r e " f i x e d " i n the wood i n some manner a r e l e a c h r e s i s t a n t and nonhygroscopic.


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Current Research The l a t e s t " D i r e c t o r y of F i r e Research i n the United States 1971 to 1973," by the N a t i o n a l Research C o u n c i l (64), shows that only a few of the l i s t e d f e d e r a l , u n i v e r s i t y , p r i v a t e , and i n d u s t r i a l l a b o r a t o r i e s a r e doing research i n v o l v i n g f i r e - r e t a r d a n t impregnation treatments f o r wood. Published r e s e a r c h i n d i c a t e s that the current e f f o r t i s i n the development of l e a c h - r e s i s t a n t types of f i r e - r e t a r d a n t treatments f o r both e x t e r i o r and i n t e r i o r uses. Major emphasis i s on r e d u c t i o n of flame spread as determined by ASTM E84 (34), and r e d u c t i o n of flaming and f i r e p e n e t r a t i o n as determined by ASTM E108 (65). Development i s a l s o d i r e c t e d toward enhanced p r o p e r t i e s of the t r e a t e d wood i n nonh y g r o s c o p i c i t y , g l u a b i l i t y , p a i n t a b i l i t y , s t r e n g t h , and preserva t i o n against biodégradation. Some a t t e n t i o n — b u t not e n o u g h — i s being g i v e n to r e d u c t i o n of smoke and noxious gases. The c u r r e n t r e s e a r c h emphasis on the t o x i c o l o g i c a l and p h y s i o l o g i c a l e f f e c t s from the combustion products of n a t u r a l and s y n t h e t i c polymers i s expected to e v e n t u a l l y i n c l u d e f i r e - r e t a r d a n t - t r e a t e d wood. FPL Research At the U.S. Forest Products Laboratory, many of the r e s e a r c h programs i n v o l v e f i r e - r e t a r d a n t - t r e a t e d wood. This has i n c l u d e d extensive b a s i c study of p y r o l y s i s and combustion r e a c t i o n s of wood and i t s components and the e f f e c t s of chemical a d d i t i v e s on these r e a c t i o n s (15,24-26,28,29,66). A cooperative study (9) w i t h the D i v i s i o n of Chemical Development of the Tennessee V a l l e y A u t h o r i t y , showed the e f f e c t i v e n e s s of l i q u i d ammonium p o l y phosphate f e r t i l i z e r s as f i r e r e t a r d a n t s f o r wood. The commercial use of these products, made from e l e c t r i c furnace superphosphoric a c i d , has been shown t o be economically f e a s i b l e . Work has been completed by Schaffer (33) on the r a t e of f i r e p e n e t r a t i o n i n wood t r e a t e d w i t h d i f f e r e n t types of chemicals. Some r e s u l t s of t h i s study a r e reported elsewhere i n t h i s paper. Studies a r e c u r r e n t l y being conducted on smoke development and heat r e l e a s e r a t e from t r e a t e d and untreated wood and wood products (52,56). An e v a l u a t i o n of the a v a i l a b l e treatment systems f o r wood s h i n g l e s and shakes was completed using a r t i f i c i a l weathering (11). A f u r t h e r development from t h i s work was a new ASTM Standard Method D2898 (67,68) f o r t e s t i n g d u r a b i l i t y of f i r e - r e t a r d a n t treatment of wood. Other I n s t i t u t i o n s Using f u l l - s c a l e f i r e t e s t f a c i l i t i e s of the I l l i n o i s I n s t i t u t e of Technology-Research I n s t i t u t e ( I I T R I ) , C h r i s t i a n and Waterman (69) studied f i r e and smoke behavior of i n t e r i o r f i n i s h m a t e r i a l s i n c l u d i n g f i r e - r e t a r d a n t - t r e a t e d wood products. The authors found that the m a t e r i a l s performed according to a



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" r e l a t i v e hazard" p o s i t i o n , but that the t u n n e l t e s t flame-spread number does not q u i t e p l a c e them i n the proper o r d e r . They s t a t e that "attempts to d i s t i n g u i s h between hazards of m a t e r i a l s whose tunnel t e s t flame-spread numbers d i f f e r by 25 or l e s s do not seem j u s t i f i e d . " These same IITRI r e s e a r c h e r s (70) a l s o found t h a t i n some s i t u a t i o n s a s i g n i f i c a n t amount of m a t e r i a l w i t h a flame spread of 90 can be s a f e l y used on w a l l s of c o r r i d o r s wider than 6 f e e t when the c e i l i n g m a t e r i a l has a r a t i n g of 0 to 25. E f f e c t i v e f i r e - r e t a r d a n t treatments f o r wood f o r e x t e r i o r uses under c o n d i t i o n s of l e a c h i n g and weathering have been needed f o r many y e a r s . For wood s h i n g l e or shake r o o f i n g , a commercial treatment system has been developed (61) i n the United S t a t e s t h a t meets acceptance requirements of U n d e r w r i t e r s L a b o r a t o r i e s , Inc. Lumber and plywood are a l s o a v a i l a b l e w i t h t h i s e x t e r i o r - t y p e treatment. The success of t h i s treatment system i n d i c a t e d a breakthrough i n the development of a commercially s u c c e s s f u l system whereby f i r e - r e t a r d a n t chemicals are pressure impregnated i n t o the wood and f i x e d or converted to a l e a c h - r e s i s t a n t s t a t e without s e r i o u s impairment of the d e s i r a b l e n a t u r a l wood p r o p e r t i e s . This d e v e l opment has s t i m u l a t e d research w i t h l e a c h - r e s i s t a n t type treatments. Chemicals employed u s u a l l y i n v o l v e o r g a n i c phosphates and compounds t h a t can r e a c t w i t h phosphorous-containing chemicals or w i t h the wood c e l l u l o s e s t r u c t u r e to g i v e permanence of treatment. The E a s t e r n F o r e s t Products Laboratory (12,71) a t Ottawa, Ontario, has been a c t i v e i n development of l e a c h - r e s i s t a n t t r e a t ments u s i n g melamine or urea w i t h dicyandiamide, formaldehyde, and phosphoric a c i d . Decay r e s i s t a n c e i s a l s o shown f o r a ureabased treatment (72). One stystem has met the requirements f o r C l a s s C wood r o o f i n g under ASTM El08 by Underwriters' Labora t o r i e s of Canada (12,73). This treatment, or one s i m i l a r , i s expected to be introduced i n t o the United States w i t h i n the year as an approved e x t e r i o r - t y p e l e a c h - r e s i s t a n t treatment. McCarthy and coworkers (74) a t the A u s t r a l i a n F o r e s t Products Laboratory reported t h a t a pressure treatment f o r p i n e posts w i t h zinc-copper-chromium-arsenic-phosphorus p r e s e r v a t i v e produced a l e a c h - r e s i s t a n t treatment having both f i r e retardancy and p r e s e r v a t i o n a g a i n s t decay. This treatment system i s r e p o r t e d to have commercial a p p l i c a t i o n i n A u s t r a l i a . B a s i c r e s e a r c h on the chemistry of c e l l u l o s i c f i r e s i s being s t u d i e d by Shafizadeh at the U n i v e r s i t y of Montana (75,76). Working w i t h model compounds, he has shown how thermal r e a c t i o n s a f f e c t the cleavage of the g l y c o s i d i c bond w i t h breakdown of the sugar u n i t s through a t r a n s g l y c o s y l a t i o n mechanism which event u a l l y r e s u l t s i n formation of combustible t a r and v o l a t i l e p y r o l y s i s products. I n t e r f e r e n c e of the t r a n s g l y c o s y l a t i o n process by a c i d i c a d d i t i o n s , amino groups, and phosphate and halogen d e r i v a t i v e s has been demonstrated to r e t a r d combustion by producing more water and char. 1



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One area of c o n t i n u i n g research a t the Stanford Research I n s t i t u t e (SRI) i s concerned w i t h the e f f e c t s of flame r e t a r d a n t s on thermal degradation of c e l l u l o s e (77,78). The r e s u l t s of a recent study (78) f o r t r e a t i n g wood showed t h a t e x i s t i n g wood r o o f s can be g i v e n a s e l f - h e l p f i r e - r e t a r d a n t treatment equiva l e n t t o a C l a s s C (65) r a t i n g f o r a 5-year p e r i o d . To o b t a i n adequate depth of p e n e t r a t i o n , the treatment i s e f f e c t i v e o n l y on weathered s h i n g l e or shake r o o f s a t l e a s t 5 years o l d . The t r e a t ment c o n s i s t s of a spray a p p l i c a t i o n of a 20 percent aqueous s o l u t i o n of diammonium phosphate, f o l l o w e d by a 20 percent aqueous s o l u t i o n of magnesium s u l f a t e to form the w a t e r - i n s o l u b l e magnesium ammonium phosphate. Of p a r t i c u l a r i n t e r e s t i s the a p p l i c a t i o n of the P a r k e r L i p ska model f o r s e l e c t i n g f i r e r e t a r d a n t s (77). This model of p y r o l y s i s processes p r e d i c t s the e f f i c i e n c y of candidate chemical f i r e r e t a r d a n t s based on increased char y i e l d and e l i m i n a t i o n of f l a m i n g . E f f i c i e n t r e t a r d a n t s w i l l be those t h a t have h i g h oxygen content per molecule and c o n t a i n phosphorus or boron to prevent a f t e r g l o w . I n a d d i t i o n , the s t u d i e s a t SRI have shown thaj: the o p t i m a l add-on weight of a chemical r e t a r d a n t i s about 10 mole per gram of c e l l u l o s e . Areas of Needed Research From the v i e w p o i n t of l i f e s a f e t y , the most urgent area of f i r e-r etardant r e s e a r c h i s the development of treatments f o r wood t h a t w i l l reduce not o n l y flame spread but a l s o smoke and noxious gases. The treatments should not add or c r e a t e new noxious gases. B a s i c r e s e a r c h on the combustion of wood being conducted i n many l a b o r a t o r i e s should be s t u d i e d and c a r e f u l l y gleaned f o r c l u e s on treatment chemicals or other means to a l t e r the c e l l u l o s e and l i g n i n s t r u c t u r e t o reduce smoke and harmful gases. Because comb u s t i o n products have been shown to be the primary cause of death i n f i r e s , r e s e a r c h on the r e d u c t i o n of smoke and gases should take precedence over r e d u c t i o n of flame spread. Another area of necessary r e s e a r c h i s development of treatments t h a t w i l l i n c r e a s e r e s i s t a n c e of wood to f i r e pene t r a t i o n . The work done by Schaffer (31,33) and others i n t h i s f i e l d should be c a r r i e d f u r t h e r . The slow r a t e of f i r e penet r a t i o n i n t h i c k wood members i s one of the b a s i c a s s e t s of wood and has been accepted and u t i l i z e d f o r many years i n heavy timber c o n s t r u c t i o n . But t h i n wood members and p a n e l i n g have a cons i d e r a b l y higher f i r e p e n e t r a t i o n r a t e than t h i c k wood members under severe f i r e c o n d i t i o n s . A f i r e - r e t a r d a n t system t h a t w i l l g i v e slower f i r e p e n e t r a t i o n means more a v a i l a b l e s a f e t y time f o r f i r e f i g h t i n g personnel and f o r evacuation of occupants from a burning b u i l d i n g . Continuing b a s i c r e s e a r c h i s needed i n the p y r o l y s i s , combustion, and f i r e chemistry of wood l e a d i n g toward the



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s e l e c t i o n of f i r e - r e t a r d a n t chemicals and t h e i r more e f f i c i e n t a p p l i c a t i o n to wood. The h i g h l o a d i n g r e q u i r e d (2 to 6 pounds of dry chemical per cubic f o o t of wood) f o r chemicals i n present use puts a severe l i m i t a t i o n on cost of usable treatments. A higher cost t r e a t ment could be t o l e r a t e d i f i t proved more e f f i c i e n t . A l a r g e p a r t of t h e c o s t of t r e a t e d wood to the consumer i s the f u l l - c e l l pressure process r e q u i r e d by present-day f o r m u l a t i o n s . A l e s s c o s t l y method of g e t t i n g the chemical i n t o the wood i s needed. We need not l i m i t the choice of chemical candidates o n l y to those that can be used i n a w a t e r - t r e a t i n g s o l u t i o n . A p p l i c a t i o n w i t h hydrocarbon s o l v e n t s or l i q u i f i e d gases w i t h subsequent recovery of the c a r r i e r may prove p r a c t i c a b l e . Further research should be d i r e c t e d toward the development of t e s t methods to p r o p e r l y evaluate f i r e - r e t a r d a n t - t r e a t e d wood. Current methods have been c r i t i c i z e d (79) f o r not g i v i n g a t r u e hazard e v a l u a t i o n of m a t e r i a l s on t h e i r p o t e n t i a l performance i n a r e a l f i r e . The l i m i t a t i o n s of s m a l l - s c a l e t e s t methods should be understood as adequate only f o r products research and d e v e l opment . Even the 25-foot r a t i n g furnace of ASTM E84 (34) has been c r i t i c i z e d regarding i t s c o r r e l a t i o n w i t h f u l l - s c a l e f i r e s and the meaning of the numbers i t produces f o r flame spread and smoke d e n s i t y (40,69,80). There i s a trend toward more f u l l - s c a l e f i r e t e s t i n g w i t h the o b j e c t i v e of r e l a t i n g the r e s u l t s of s m a l l e r s c a l e t e s t s i n c l u d i n g the 25-foot furnace to performance i n r e a l f i r e s . F u l l - s c a l e t e s t s a r e too expensive, of course, to prove out b u i l d i n g products on a r o u t i n e b a s i s . Perhaps the c o r n e r - w a l l t e s t (80-82) i s adequately r e a l i s t i c and could be used i n conj u n c t i o n w i t h s m a l l - s c a l e t e s t s f o r determining product performance and f i r e hazard. As new c r i t e r i a a r e developed f o r d e f i n i n g c o m b u s t i b i l i t y , a method i s needed to r e a l i s t i c a l l y i n d i c a t e heat r e l e a s e r a t e of wood products exposed to b u i l d i n g f i r e s i n s t e a d of dependence on " t o t a l heat v a l u e s . " Continuing research must y i e l d i n f o r m a t i o n on t h e treatmentr e l a t e d p r o p e r t i e s of f i r e - r e t a r d a n t - t r e a t e d wood and methods f o r t h e i r improvement. The p r o p e r t i e s of the c o n v e n t i o n a l s a l t t r e a t ments which need improvement e s p e c i a l l y a r e h y g r o s c o p i c i t y , s t r e n g t h p r o p e r t i e s , g l u i n g , and f i n i s h i n g .


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Literature Cited


1.

National Commission on Fire Prevention and Control "America burning: The report of the national commission on fire prevention and c o n t r o l . " 53 p. Washington, DC. 1973. 2. American Wood Preservers' Association "Wood preservation s t a t i s t i c s 1974." Compiled by Ernst & Ernst, In Am. Wood Preserv. Assoc. Proc. 71:225-263. AWPA, Washington, DC. 1975. 3. Lyons, J. W. "The chemistry and uses of f i r e retardants." WileyInterscience Div., John Wiley and Sons, New York. 1970. 4. Goldstein, I. S. Degradation and protection of wood from thermal attack. In "Wood Deterioration and Its Prevention by Preservative Treatment. Vol 1. Degradation and Protection of Wood," p. 307-339. D. D. Nicholas, ed. Syracuse Univ. Press. Syracuse, N.Y. 1973. 5. Browne, F. L. U.S.D.A. For. Prod. Lab. Rep. No. 2136, Madison, Wis. 1958. 6. Juneja, S. C. Synergism and fire retardance of wood and other c e l l u l o s i c materials. In "Advances in Fire Retardants, Part 2." V. M. Bhatnagar, ed. Technomic, Westport, Conn. 1973, 7. Juneja, S. C. Wood Sci. 7(3):201-208. 1975. 8. Eickner, H. W. J. Mater. 1(3):625-644. 1966. 9. Eickner, H. W., J. M. Stinson, and J. E. Jordan Am. Wood Preserv. Assoc. Proc. 65:260-271. 1969. 10. Eickner, H. W., and E. L. Schaffer Fire Tech. 3(2):90-104. 1967. 11. Holmes, C. A. Evaluation of fire-retardant treatments for wood shingles, Ch. 2. In "Advances i n F i r e Retardants, Part 1." V. M. Bhatnagar, ed. Technomic, Westport, Conn. 1971. 12. Juneja, S. C., and L. R. Richardson For. Prod. J. 24(5):19-23. 1974. 13. Kanury, A. M. Fire Res. Abstr. and Rev. 14(1):24-52. 1972. 14. Matson, A. F., R. E. Dufour, and J. F. Breen Bull, of Res. No. 51, p. 269-295. Underwriters' Lab. Inc., Northbrook, Ill. 1959. 15. B e a l l , F. C., and H. W. Eickner U.S.D.A. For. Serv. Res. Pap. FPL 130, For. Prod. Lab., Madison, Wis. 1970. 16. U.S. Forest Products Laboratory. U.S.D.A. For. Prod. Lab. Rep. No. 1464 ( r e v . ) , Madison, Wis. 1958.


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17.

McGuire, J. H. F i r e Technol. 5(3):237-241. 1969. 18. National Fire Protection Association "Fire protection handbook." 13th ed. pp. 1-7, 5-7. N a t l . F i r e Prot. Assoc. Boston, Mass. 1969. 19. Broido, A. Chem. Tech. 3(1):14-17. 1973. 20. Prince, R. E. "Tests on the inflammability of untreated wood and of wood treated with fire-retarding compounds". In Publ. Proc. of Annu. Meet. N a t l . Fire Prot. Assoc. Boston, Mass. 1915. 21. Shafizadeh, F. Pryolysis and combustion of c e l l u l o s i c materials. In "Advances i n Carbohydrate Chemistry." V o l . 23, pp. 419-474. M. L . Wolfrom, and R. S. Tipson, eds. Academic press, New York. 1968. 22. MacLean, J. D. Am. Wood Preserv. Assoc. Proc. 47:155-168. 1951. 23. Stamm, A. J . Ind. and Eng. Chem. 48(3):413-417. 1956. 24. B e a l l , F. C. Wood Sci. 5(2):02-108. 1972. 25. Brenden, J. J. U.S.D.A. For. Serv. Res. Pap. FPL 80, For. Prod. Lab., Madison, Wis. 1967. 26. Browne, F. L., and J. J. Brenden U.S. For. Serv. Res. Pap. FPL 19, For. Prod. Lab., Madison, Wis. 1964. 27. Shafizadeh, F . , P. Chin, and W. DeGroot J. F i r e & Flammability/Fire Retardant Chem. 2:195-203. Aug. 1975. 28. Tang, W. K. U.S. For. Serv. Res. Pap. FPL 71, For. Prod. Lab., Madison, Wis. 1967. 29. Tang, W. Κ., and H. W. Eickner U.S. For. Serv. Res. Pap. FPL 82, For. Prod. Lab., Madison, Wis. 1968. 30. American Society for Testing and Materials ASTM Design. E119-73. Philadelphia, Pa. 1973. 31. Schaffer, E. L . U.S. For. Serv. Res. Pap. FPL 69, For. Prod. Lab., Madison, Wis. 1967. 32. Great B r i t a i n Ministry of Technology and Fire Offices' Committee, Joint F i r e Research Organization "Fire research 1964." Rep. of the F i r e Res. Board with the Rep. of the D i r . of F i r e Res. p. 12. London. 1965. 33. Schaffer, E. L . J. Fire & Flammability, Fire Retardant Chem. Suppl. 1:96-109, A p r i l 1974.


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34.

103

American S o c i e t y f o r T e s t i n g and M a t e r i a l s ASTM Desig. E84-75. P h i l a d e l p h i a , Pa. 1975. 35. U n d e r w r i t e r s ' L a b o r a t o r i e s , Inc. " W o o d — f i r e hazard classification, card data s e r v i c e . " Serial No. UL527. U n d e r w r i t e r s ' L a b o r a t o r i e s , I n c . , Northbrook, Ill. 1971. 36. U n d e r w r i t e r s ' L a b o r a t o r i e s , I n c . " B u i l d i n g m a t e r i a l s d i r e c t o r y P a r t I." B u i l d . Mater. List. Underwriters' L a b o r a t o r i e s , I n c . , Northbrook, Ill. Jan. 1976. 37. American S o c i e t y f o r T e s t i n g and M a t e r i a l s ASTM Design. E286-69 (reapproved 1975). P h i l a d e l p h i a , Pa. 1969. 38. H a l p i n , Β. Μ., E. P. Radford, R. F i s h e r , and Y. Caplan Fire J . 69(3):11-13, and 98-99. 1975. 39. Thomas, D. M. Fire Command 38(4):23-27. 1971. 40. Yuill, C. H., e t . al. Task Group of Subcomm. IV of ASTM Comm. E-5 on Fire Tests of Mater, and C o n s t r . , Mater. Res. and Stand., MTRSA 11(4):16-23, 42. 1971. 41. Brenden, J . J . For. Prod. J. 21(12):22-28. 1971. 42. Lee, T. G. "The smoke d e n s i t y chamber method f o r e v a l u a t i n g the potential smoke g e n e r a t i o n of b u i l d i n g m a t e r i a l s , " U.S. Dep. Commer., Natl. Bur. Stand., Tech. Note No. 757. 1973. 43. N a t i o n a l f i r e P r o t e c t i o n A s s o c i a t i o n N a t l . Fire P r o t . Assoc. NFPA No. 258. Boston, Mass. 1976. 44. Einhorn, I. N., D. A. Chatfield, J . H. Futrell, R. W. M i c k e l s o n , K. J . Voorhees, F. D. Hileman, and P. W. Ryan "Methodology f o r the a n a l y s i s of combustion p r o d u c t s . " UTEC 75-073, FRC/UU49. Univ. of Utah, S a l t Lake C i t y , Utah. 1975. 45. Goos, A. W. The thermal decomposition of wood, Ch. 20. In "Wood Chemistry." L.E. Wise and E. C. Jahn, eds. 2nd ed. R e i n h o l d , New York. 1952. 46. Wagner, J. P. Fire Res. A b s t r . and Rev. 1 4 ( 1 ) : 1 - 2 3 . 1972. 47. B i r k y , M. M. Polymer P r e p r . 14(2):1011-1015. 1973. 48. Einhorn, I. Ν., M. M. B i r k y , M. L. Grunnet, S. C. Packham, J. Η. Petajan, and J . D. Seader "The p h y s i o l o g i c a l and toxicological aspects of smoke produced during the combustion of polymeric m a t e r i a l s . " Annu. r e p . 1973-1974. UTEC-MSE 74-060, FRC/UU26. Univ. of Utah, S a l t Lake C i t y , Utah. 1974.


104 49. J. 50.


51.

52. 53. J. 54. 55. 56. 57. 58.

59.

60.

61. 62. 63. 64.

WOOD TECHNOLOGY: CHEMICAL ASPECTS O'mara, M. M. F i r e & Flammability 5(1):34-53. 1974. Robison, Μ. Μ., P. E. Wagner, R. M. Fristrom, and A. G. Schulz F i r e Technol. 8(4):278-290. 1972. Birky, M. M. "Review of smoke and toxic gas hazards i n fire environment." Int. Symp. F i r e Safety of Combust. Mater., Univ. of Edinburgh, Scotland. Oct., 1975. Brenden, J. J. U.S.D.A. For. Serv. Res. Pap. FPL 249, For. Prod. Lab., Madison, Wis. 1975. Satonaka, S., and K. Ito Jap. Wood Res. Soc. 21(11):611-617. 1975. Loftus, J. J., D. Gross, and A. F. Robertson "Potential heat of materials i n building fires." U.S. Dep. Commer., N a t l . Bur. Stand., Tech. News Bull. 1962. Smith, Ε. E. F i r e Technol. 12(1):49-54. 1976. Brenden, J. J. U.S.D.A. For. Serv. Res. Pap. FPL 230, For. Prod. Lab., Madison, Wis. 1975. Gerhards, C. C. U.S.D.A. For. Serv. Res. Pap. FPL 145, For. Prod. Lab., Madison, Wis. 1970. Brazier, J. D., and R. A. Laidlaw "The implications of using inorganic salt flame-retardant treatments with timber." BRE Information IS 13/74. In News of Timber Res. Princes Risborough Lab., Aylesbury, Buckinghamshire. Dec. 1974. National Forest Products Association "National design specifications for stress-grade lumber and its fastenings." N a t l . For. Prod. Assoc., Washington, DC. 1973. U.S. Forest Products Laboratory. "Wood handbook: Wood as an engineering material." pp. 15-10, 15-11. U.S.D.A. Agric. Handb. No. 72, (rev)., 1974. Shunk, Β. H. For. Prod. J. 22(2):12-15. 1972. Schaeffer, R. E. U.S.D. A. For. Serv. Res. Note FPL-0160, For. Prod. Lab., Madison, Wis. 1968. Baker, A. J. U.S.D.A. For. Serv. Res. Pap. FPL 229, For. Prod. Lab., Madison, Wis. 1974. National Research Council "Directory of f i r e research i n the United States 19711973." Comm. on F i r e Res., Div. Engr., N a t l . Res. Coun., N a t l . Acad. Sci., Washington, DC. 1975.


6.

HOLMES

Fire-Retardant Treatment


65. ASTM 66.

105

American Society for Testing and Materials Desig. E108-75. Philadelphia, Pa. 1975. Browne, F. L., and W. H. Tang U.S. For. Serv. Res. Pap. FPL 6, For. Prod. Lab., Madison, Wis. 1963. 67. American Society for Testing and Materials ASTM Desig. D2898-72. Philadelphia, Pa. 1972. 68. Holmes, C. A. U.S.D.A. For. Serv. Res. Pap. FPL 194, For. Prod. Lab. Madison, Wis. 1973. 69. Christian, W. J., and T. E. Waterman F i r e . Tech. 6(3):165-178, 188. 1970. 70. Christian, W. J., and T. E. Waterman F i r e J. 65(4):25-32. 1971. 71. King, F. W., and S. C. Juneja For. Prod. J. 24(2):18-23. 1974. 72. Juneja, S. C., and J. K.Shields For. Prod. J. 23(5):47-49. 1973. 73. Fung, D.P.C., Ε. E. Doyle, and S. C. Juneja Inf. Rep. OP-X-68, Dep. of the Environ., Canadian For. Serv., Eastern For. Prod. Lab., Ottawa, Ont. 1973. 74. McCarthy, D. F., W. G. Seaman, E.W.B. DaCosta, and L.D. Bezemer J. Inst. Wood Sci. 6(1):24-31. 1972. 75. Shafizadeh, F. Appl. Polymer Symp. 28, Proc. of the Eighth Cellulosic Conf., Part I , pp. 153-174. T. E. Timell, ed. John Wiley and Sons, N.Y. 1975. 76. Shafizadeh, F. J. of Appl. Polymer S c i . 12(1):139-152. 1976. 77. Amaro, A. J., and A. E. Lipska "Development and evaluation of p r a c t i c a l self-help fire retardants. Annual Report." SRI Proj. No. PYU-8150. Stanford Res. I n s t . , Menlo Park, C a l i f . 1973. 78. Lipska, Α. Ε., and A. J. Amaro "Development and evaluation of p r a c t i c a l and self-help fire retardants. F i n a l Report." SRI Proj. No. PYU-8150. U.S. Dep. Commer., NTIS No. AD-A014 492. Stanford Res. I n s t . , Menlo Park, C a l i f . 1975. 79. Yuill, C. H. Am. Soc. Test. Mater. Stand. News, STDNA 1(6) :26-28, 47. 1973. 80. Williamson, R. Β., and F. M. Baron J. Fire & Flammability 4(2):99-105. 1973. 81. Underwriters' Laboratories, Inc. "Flammability studies of c e l l u l a r p l a s t i c s and other building materials used i n i n t e r i o r finishes." Subj. 723. Underwriters' Laboratories, Northbrook, Ill. 1975.


106

U.S. Forest Products Laboratory. U.S.D.A. For. Serv. Res. Note FPL-0167. For. Prod. Lab., Madison, Wis. 1967.


82.

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