However, many of the effective poisonous chemicals were questionable. Increased public concern on the environmental effect of many wood preservatives has rendered special importance to borates as an environmentally friendly agent. Boron compounds are well known preservative chemicals for timber protection. They are recognized as cheap, easily applicable, biologically active, flame retardant and, more importantly, environmentally safe preservatives and have been used for timber preservation since the early twentieth century (Williams 1990, Lloyd 1993, Laks and Manning 1994). Boron containing chemicals such as boric acid (BA) and borax (BX) are the most common boron compounds which have found many application areas in the wood preservation industry in order to obtain the benefit of their fire retardancy (Hafi zoglu et al. 1994, Baysal 1994). Fire retardant chemicals drastically reduce the rate at which flames travel across the wood surface, thereby reducing the capacity of the wood to contribute to a fi re (LeVan et al. 1990). However, wood strength is effected when wood is treated with preservatives or fi re retardant (FR) chemicals (Winandy 1988). The relative impact of various waterborne preservative systems is directly related to the system’s chemistry and the severity of its fi xation/precipitation reaction (Winandy 1996). Degradation depends on the fi re-retardant formulation (LeVan et al., 1990); exposure temperature and relative humidity (Winandy et al. 1991). Winandy (1995) determined that there appears to be a little relative difference in their effect on strength when retention levels of chemicals were between 4.0 to 9.6 kg /m3. Barnes et al. (1990) found that mechanical property reductions for wood treated to terrestrial retentions and redried at temperatures less than 70 °C are insignificant, while treating to higher retentions and/or redrying at higher temperatures can cause significant strength loss. Winandy et al. (1988) noticed that the effects of fi re retardant treatments on mechanical properties of Douglas- fi r and aspen plywood. They found that copper zinc chlorite (CZC) treatment had a far greater negative effect than did the other FR treatments. It is probable that the high level of chlorite in CZC treatment promoted hydrolysis via an intermediate formation of hydrochloric acid. Wazny and Krajeweski (1992) reported that chromated copper arsenate (CCA) and sodium pentachlorophenol (NAPCP) treatments did not have any practical consequences on compression strength of wood.