Flammability oxygen availability

For any chemical reaction to take place it is known that definite quantities of constituents are necessary. The quantity of oxygen available in the air near flammable material can only oxidize/bum a certain quantity of the flammable material. A commonly known term, stoichiometric ratio, is responsible for determining the quantity of oxygen necessary to react with available flammable materials. Naturally, when the quantity of the flammable material and the available atmospheric oxygen are near to the stoichiometric ratio, the reaction will be near completion and cause an explosion with increase in temperature and pressure. The explosion will be violent. When the quantity of flammable material is too small, combustion carmot spread and may cease. The situation is similar when the quantity of flammable material is too large, because the lack of the required quantity of O2 means that the reaction carmot proceed further. As indicated in an earlier clause (Fig. X/3.1.2-1), all flammable materials have their explosion ranges and limits LEL and UEL. It may be possible to dilute flammable materials in excess air, but it is very difficult to create a situation where there is a dearth of oxygen because of the work force, hence this is only applicable inside equipment. 

At the lower limit of flammability there is more oxygen available than is required for stoichiometric combustion of the fuel. For example, the lower flammability limit for propane in air at 20 C is 2.2% by volume. 

Note 2 Warning—Extremely flammable liquefied gas under pressure. Vapor reduces oxygen available for breathing. 

Extreme caution must be taken to prevent the possibility of fire when using flammable removers. Extra care must be taken when stripping on location to secure the area of ignition sources. When used on lacquer finishes, the dissolved finish and remover combined are extremely flammable. Natural mbber, neoprene, or other gloves suitable for use with the remover formula must be worn. The effect of skin contact with the remover is limited because there is immediate irritation and discomfort. Canister respirators are available for most petroleum and oxygenate remover solvents. Symptoms of long-term overexposure should be compared to symptoms of the major ingredients in the formula. 

For a catalyst-ignited fire to occur, oxygen must be present exclusion of oxygen permits completely safe handling. Some workers put the catalyst in the reaction vessel and sweep air from the vessel with a gentle flow of nitrogen or carbon dioxide argon is ideal if available, The solvent, which may be cooled to diminish its flammability, is then added. Once all of the catalyst has been wet with solvent, fire will not occur. Air can also be removed from the flask by... 

The ACGIH has not assigned a numerical threshold limit value (TLV) for occupational exposure to methane because the limiting factor is the available oxygen, the minimal content of which should be 18% by volume under normal atmospheric pressure at concentrations below those required to produce any severe oxygen deprivation, methane presents an explosive and flammable hazard. ... 

Where this value is known it is an excellent measure of the relative hazard of a flammable liquid. Unfortunately, it is available in only a few instances Susceptibility to Spontaneous Heating. Many materials combine with atmospheric oxygen at ordinary temperatures and liberate heat. If the heat is evolved faster than it is dissipated due to poor housekeeping, a fire can start, particularly in the presence of easily ignited waste, etc. [ Factory Mutual Modified Mackey Method, Industrial and Engineering Chemistry (March 1927)] Explosive Range or Flammability Limits. 

In many cases, CO2 is seen as the most viable supercritical solvent. It is inexpensive and readily available (by-product of fermentation and combustion), non-toxic and non-flammable. It cannot be oxidised and therefore oxidation reactions using air or oxygen as the oxidant have been intensively investigated. In addition, it is inert to free-radical chemistry, in contrast to many conventional solvents. 

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