Flammability, physical state requirement

Flammable limits apply to all fuels regardless of their initial physical state. Thus, liquids and solids also have a required minimum amount of fuel that must be present before ignition can occur. 

The properties and physical chemistry of liquid and supercritical carbon dioxide have been extensively reviewed (Kiran and Brennecke, 1992), as have many fundamentals and applications for separation, chromatography, and extraction (McHugh and Krukonis, 1994). The phase diagram for pure C02 is illustrated in Figure 1.1. Due to its relatively low critical point, C02 is frequently used in the supercritical state. Other common supercritical fluids require higher temperatures and pressures, such as water with Tc = 374.2 °C and Pc = 220.5 bar, while propane (Tc = 96.7 °C and Pc = 42.5 bar) and ethane (Tc = 32.2 °C and Pc = 48.8 bar) have lower critical pressures but are flammable (McHugh and Krukonis, 1994). 

A substance is a hazardous chemical if it is a physical hazard or a health hazard . A flammable or explosive liquid is a physical hazard . A flammable liquid means any liquid having a flash point below 110°F (37.8°C), except any mixture having components with flash points of 100°F (37.8°C) or higher, the total of which make up 99% or more of the total volume of the mixture . Health hazard means a chemical for which there is statistically significant evidence based on at least one valid study that acute or chronic health effects may occur in exposed employees . Hexane and all the solvents listed in Table 13.10.3 would require a MSDS, since all are flammable liquids (physical hazards) as defined by OSHA and/or possible health hazards because all, except hexane isomers, have an U.S. OSHA PEL. However, hexane isomers have an American Conference of Industrial Hygienist (ACGIH) dneshold limit value (TLV), which many states and countries enforce as a mandatory standard. 

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