Fiberboards 



30 



2775 



28- 



BOILED 4 HRS - SOAKED 15 HRS. 





v ^ s^ ^^ 



OVEN DRY -23 HRS. 105** C 

 •15% RESIN o257o RESIN ^ 507o RESIN 



Figure 23-24. — Thickness swell of dry-formed hardboard at three contents of impreg- 

 nating resin, during six cycles of exposure. (Drawing after Brown et al. 1966.) 



FIRE RETARDANT AND PRESERVATIVE TREATMENTS 



Fire retardants. — Fiberboard is combustible. At high temperatures it 

 evolves combustible gas which increases fire destruction, and smoke which 

 obscures vision and irritates the respiratory system. In panel materials such as 

 fiberboard and plywood, flame spread rate, fuel contribution, and smoke devel- 

 opment are the statistics of interest. Methods of measuring them, and the effec- 

 tiveness of various chemicals, are summarized in Koch (1972, p. 1 1 1 1-1 128). In 

 devices to measure flame-spread rate, untreated red oak has a rating of 100; 

 lower numerical rating indicates slower flame spread. Class A materials suitable 

 for exitways of unsprinklered. assembly and institutional buildings must have a 

 flame-spread rating of to 25; class B (flame-spread rating of 26-75) is suitable 

 for schools and hotels. Fiberboard, unless treatd with fire retardants, cannot be 

 used where codes require class A or class B ratings. 



