Flammable vapours

BLEVE, BOILING LIQUID EXPANDING VAPOUR EXPLOSION Instantaneous release and ignition of flammable vapour upon rupture of a vessel eontaining flammable liquid above its atmospherie boiling point. 

Application of heat to a flammable liquid (e.g. due to radiation or flame impingement in a fire, or because of hot work ) can generate a flammable vapour-air mixture. 

The rate of evolution of a toxie or flammable vapour from a liquid (e.g. in an open vessel, from a spillage or as a spray) is direetly related to the exposed area. Therefore, the rate of vapour formation from solvent-impregnated rag, from solvent-based films spread over a large area, from foams or from mists ean be many times greater than that from bulk liquid. 

The vapour pressure of a flammable substanee also provides an indieation of how easily the material will volatilize to produee flammable vapours the higher the vapour pressure, the greater the risk. Lists of vapour pressures usually eontain data obtained under differing eonditions but inspeetion of boiling points (when the vapour pressure equals atmospherie pressure) gives a first approximation of the ease with whieh substanees volatilize. Table 6.1 therefore ineludes both boiling point and vapour pressure data. 

Materials with high flash points sueh as heavy oils and resins ean produee flammable vapours due to thermal degradation on heating. Dangers therefore arise when welding, flame eutting empty drums/vessels onee used to eontain sueh materials due to the presenee of residues. 

Ignition of a flammable dust-air mixture is more difficult than with flammable vapour-air mixtures. A larger source of heat is required, and a larger volume of fuel must be heated to the ignition point. The same range of potential ignition sources is applicable as for air-vapour mixtures. 

Liquid earbon dioxide produees a eolourless, dense, non-flammable vapour with a slightly pungent odour and eharaeteristie aeid taste . Physieal properties are given in Table 8.5 (see also page 277). Figure 8.1 demonstrates the effeet of temperature on vapour pressure. 

For zero adjustment, place instrument in uncontaminated air or use activated charcoal filters to remove flammable vapours... 

Drums eontaining flammable liquids are preferably stored outside, so that any flammable vapour ean readily disperse. Similar eonsiderations may apply to the dispersion of any vapour/fumes from drums of toxie liquids or solids. In some eases weather proteetion is provided by a roof. 

Since few chemicals (e.g. hydrogen, methane, ammonia) have a molecular weight less than that of air, under ambient conditions most gases or vapours are heavier than air. For example, for common toxic gases refer to Table 3.1 for flammable vapours refer to Table 5.1. At constant pressure the density of a gas or vapour is, as shown, inversely proportional to the absolute temperature. As a result ... 

The rate of evolution of a toxic or flammable vapour from a liquid (e.g. in an open... 

Liquid carbon dioxide produces a colourless, dense, non-flammable vapour with a... 

It reacts violently with water, and on heating produces flammable vapour which may explode if mixed with air and ignited. 

During the distillation of hexane from potassium hydroxide pellets, it was found that the 2 1 flask had become perforated by alkaline attack, and that hexane was leaking through two pinholes, generating much flammable vapour. The high rate... 

One of the main attractions of SCF solvents is the ease of separating products at the end of the reaction. For products which are liquids, phase separation can be achieved merely by reducing the pressure. However, it should be remembered that some of the SCF will still remain dissolved in the liquid phase. This may not be a problem in reactions carried out in SCCO2 but it could present difficulties for products isolated on a large scale from flammable SCFs, where outgassing of flammable vapour from the liquid product could occur. 

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