Contact explosives, defined

Flammable Limits The minimum and maximum concentration of fuel vapor or gas in a fuel vapor or gas/gaseous oxidant mixture (usually expressed in percent hy volume) defining the concentration range (flammable or explosive range) over which propagation of flame will occur on contact with an ignition source. See also Lower Flammable Limit and Upper Flammable Limit. 

Fuel properties are especially important in defining the safety hazards posed by a fuel. Since fuels are flammable, fire and explosion hazards are possible. Some fuels are toxic or contain carcinogenic compounds that present exposure, inhalation, and ingestion hazards. Fuels stored at cryogenic temperatures such as liquefied natural gas and liquefied hydrogen present safety hazards from skin contact... 

Dinitroethane is a very powerful explosive, giving a lead block expansion of 140-150 (picric acid = 100). Its density is 1.46. It is less sensitive to impact than picric acid. Since it is highly reactive, and hence unstable, it has not found any use as explosive. It reacts most readily with bases. For example, when stored in a glass vessel it decomposes after a few weeks as the result of its contact with glass, which has basic properties. Levy suggests adding to the product an organic acid, as for example p- toluenesulphonic acid, as a stabilizer. Under the influence of bases dinitroethane may form nitroethylene, as well as other less defined products, which can readily polymerize to form resinous substances. 

It should be noted that the limits so defined, which bound the region of apparent equilibrium, are by no means fixed. In the phosphorescence of phosphorus, e. g., they depend on the amount of moisture present. The combination of oxygen and hydrogen, again, is ultimately dependent on the substance with which the gases are in contact. Thus, Mitscherlich gives the temperature of explosion in glass vessels as 674° instead of 845 . 

Certain other rather stringent limitations are attached to flammable solids and liquids as to the precise conditions under which they will burn or explode. The explosive or flammable limits of a material refers to the ratio between the amount of potentially flammable vapor in mixture with ambient air or oxygen. The lower limits are defined as the minimum concentration of vapor in air or oxygen below which the propagation of flame does not occur on contact with a source of ignition. Likewise, there is a maximum concentration which ignition does not occur. As may be expected, these limits have wide variation dependent upon the particular material involved. 

The rationale for the vacuum stability test [23] is that the azide either alone or in contact with some material, at an elevated temperature, may in time, cause a reaction leading to the deterioration of the explosive and a consequent evolution of gas. Generally, 1 g of the explosive and of the material are intimately mixed and placed into a suitable vessel connected to a mercury manometer. After evacuation the mixture is heated for a fixed 40 hr or as specified. The quantity of evolved gas is noted. Reactivity is measured by the difference between the volume of gas evolved by the mixture and by a control (the pure explosive) in 40 hr. The reactivity is defined qualitatively as follows ... 

Physico-chemical hazards are those dictated directly by the chemistry or physical properties of the chemical These include explosivity (the potential to evolve highly reactive gases, with the evolution of heat, which can cause an explosion), oxidizing ability (the potential to react exothermally in contact with otha substances, particularly flammable substances) and flammability (the capability to ignite and bum). These hazards are categorised in terms of defined criteria by various regulatory bodies (for example, the EC). Radioactivity is a very unique hazard associated with molecules possessing a special electronic structure. 

Recent work by Beck 2 in developing a mechanistic model for vapor film collapse suggests that melt-coolant contact geometry is analogous to the contact conditions established in explosive welding. (This requires asymmetric vapor film collapse, as opposed to the symmetric vapor film collapse used in other models.53 one method used to analyze explosive welding conditions and their effect on performance is to define a Reynolds number that... 

---