Hexane flammability limits

Phosgene has been shown to have an effect on the flammability limits of hexane in air [1362]. At room temperature and atmospheric pressure, the upper and lower limits of... 

Combustible vapor-arr mixtures are flammable over a limited range of concentrations. The minimum volume % of vapor that gives a combustible mixture is called the lower flammable limit (LFL). Generally, the LFL is about half the stoichiometric mixture, the concentration required for complete combustion of the vapor in air. (a) If oxygen is 20.9 vol % of air, estimate the LFL for n-hexane, CgHj4. (b) What volume (in mL) of n-hexane (d = 0.660 g/cm ) is required to produce a flammable mixture of hexane in 1.000 m of air at STP ... 

They are sensitive to all flammable gases, and they give approximately the same response to the presence of the lower explosive limit (LEL) concentrations of all the common hydrocarbon gases and vapors. However it should be remembered that gas detectors do not respond equally to different combustible gases. The milli-volt signal output of a typical catalytic detector for hexane or xylene is roughly one half the signal output for methane. 

Fig. 3.3. Limits of flammability of various n-hexane-inert gas mixtures at 25°C and atmospheric pressure, courtesy Bureau of Mines)...

If desired, one could replace CCI4 with hexane (a mixture of several isomers), since hexane is not very toxic and has an exposure limit of 100 ppm vapor in the air. However, hexane is more volatile, and the distribution constant for I2 is different in different hexane isomers, leading to problems with the data analysis. Perhaps a better alternative is p-xylene. Although less toxic this solvent is however more flammable than CCI4, with a flash point of 17°C. Finally, we note that it is also possible to determine I2 concentrations spectrophotometrically, which eliminates the titrations. 

While hexane is widely accepted as the most effective solvent used today, there are concerns about its flammability, exposure, and environmental impacts. Research has focused on various alternative solvents in the hopes of finding one with acceptable performance while providing greater safety. Alternative solvents that have received some attention include isopropyl alcohol, supercritical carbon dioxide, and other fluids. However, no economical alternative to n-hexane has been accepted at this point, and the best available control technology emphasizes containment and limiting fugitive hexane emissions. 

Hazard TLV TWA 500 ppm STEL 1000 ppm (hexane isomer). Highly flammable, dangerous fire and explosion risk, explosive limits in air 1-7%. 

HEXANE or -HEXANE (110-54-3) C H,4 Highly flammable liquid extremely low ignition temperature makes it very dangerous. Forms explosive mixture with air [explosion limits in air (vol %) 1.1 to 7.5 flash point -7°F/-22°C autoignition temp 437°F/225°C Fire Rating 3]. Violent reaction with strong oxidizers bromine, chlorine, fluorine, chromic acid, sodium peroxide. Contact with dinitrogen tetraoxide may explode at 82°F/28°C. Incompatible... 

METHYL-l-PHENYL-ETHYLENE (98-83-9) C9H10 Flammable liquid. Forms explosive mixture with air [explosion limits in air (vol %) 0.9 to 6.1 flash point 129°F/54°C autoignition temp 1066°F/574°C Fire Rating 2], Easily polymerizable. Unless inhibited, forms unstable peroxides. Reacts with heat and/or lack of appropriate inhibitor concentration. Reacts with catalysts for vinyl or ionic polymerization, such as aluminum, iron chloride or 2,5-dimethyl-2,5-di(ieri-butylperoxy)hexane. Violent reaction with strong oxidizers, butyl lithium, oleum, xenon tetrafluoride. Incon atible with acids. The uninhibited monomer vapor may block vents and confined spaces by, forming a solid polymer material. Attacks aluminum and copper. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or CO2 extinguishers. 

The use of supercritical fluid extraction (SEE) as an extraction technique is related to the unique properties of the supercritical fluid. These fluids have a low viscosity, high diffusion coefficients, low toxicity, and low flammability, all clearly superior to the organic solvents used in SPE extraction. The most common fluid used is carbon dioxide. SEE extractions of sediment samples have shown recoveries of >95% for all the individual PCBs. The separation of PCDDs from PCBs and chlorinated benzenes is difficult because of their similar solubility. An interesting development is the use of fat retainers. Samples, mixed in different weight ratios with, e.g., silica/silver nitrate 10% or basic alumina, can be placed in 7 ml extraction cells. The analytes are recovered by elution with 1.5-1.8 ml of hexane. With the correct fat-silica ratios and SEE conditions, no additional cleanup procedure is necessary for GC with an electron-capture detector (ECD). One drawback of SEE may be that the methods developed are valid for a specific matrix, but as soon as, e.g., the fat content of a biota sample or the type of lipids changes, the method has to be adapted. SEE is relatively complicated compared to other extraction techniques. In addition, the cell volumes are small, which limits the sample intake, and, with that, the detection limits. Einally, some reliable types of SEE equipment have recently been withdrawn from the market. This will have a substantial negative effect on the use of SEE in the near future. 

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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