Explosion protection upper explosive limit

In the field of explosion protection of electrical apparatus and systems, the upper temperature limit is normally decreased to +40°C, and this fact should be noticed throughout all the following chapters. 

There can also be a flammability limit associated with dust clouds. The flammability limits of combustible dusts are reported as the minimum explosion concentrations. The upper explosion limits for dust clouds have not been determined due to experimental difficulties. In the fourteenth edition of the Fire Protection Handbook [National Fire Protection Association (NFPA), Boston, MA, 1975], numerous results from the U.S. Bureau of Mines reports are listed. These results were obtained with dusts 74 fim or smaller. It should be noted that variations in minimum explosive concentrations will occur with change in particle diameter, i.e., the minimum explosive concentration is lowered as the diameter of the particle decreases. Other conditions which affect this limit are sample purity, oxygen concentration, strength of ignition source, turbulence, and uniformity of the dispersion. The NFPA tabulation is most extensive and includes data for dusts from agricultural materials, carbonaceous matter, chemicals, drugs, dyes, metals, pesticides, and various plastic resins and molding compounds. Except for metal... 

National Fire Protection Association. System gives a qualitative rating for health, flammability, and spontaneity. These values range from 0 to 4, with 4 being the most hazardous. These can be used for an initial screen to sensitize engineers to the potential hazard. Quantitative values are published elsewhere for each separate issue health (TLV, STEL, IDLFl) flammability explosivity (upper and lower explosive limits). 

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