Table 2. --Lower limits of flammability of gases in air 



Gases 



Percent gas to air 



Methane 

 Propane 

 Butane 

 Ethanol 



5.00 

 2.12 

 1.86 

 3.28 

 1.85 

 4.00 

 2.75 

 2.50 

 .95 

 .80 



Diethyl ether 



Hydrogen 

 Ethylene 



Acetylene 



Octane 



Turpentine 



■'■Handbook physics and chemistry, 38th Ed., p. 1788, 

 1956-57. Chemical Rubber Publishing Co. 

 + 3 pinene 



The ether extractives (crude fat content) are composed of many compounds, including 

 oils, waxes, fats, and terpenes. Crude fat content is directly related to the total 

 energy content of plants (Bliss 1962; Philpot 1969b). These extractives could be 

 important for several reasons: first, they have a very high energy content, up to 

 23,000 B.t.u./lb, ;second, a portion of them is more available to combustion than the 

 other major components of the fuel because of their high vapor pressure and, in some 

 cases, because of their location on fuel surfaces (Philpot 1969b). Also, terpenes have 

 one of the lowest fuel/air ratios of any organic fuel (table 2) . They vary seasonally 

 in many fuels, reaching a maximum at the height of the fire season (Philpot 1969b; 

 Richards 1940). For example, consider the trend in ether extractives in aspen leaves 

 during the 1968 fire season in western Montana (fig. 1). The energy increase in fuels 

 during the fire season is due mainly to extractive accumulation or changes in 

 extractive composition. 



14 



7 



JUNE 



JULY 



AUG, 



SEPT. 



OCT. 



Figure 1. — The trend of 

 ether extractive content 

 in aspen during the fire 

 season in western Montana. 



3 



