Incendivity

Mechanically generated hot surfaces represent an ignition hazard if, irrespective of the MIT and the MIE, the. surface temperature is 1100°C or higher and the hot. surface area by itself is large enough (see Fig. 26-35). Higher surface temperatures and larger surfaces have a better incendivity lower temperatures and smaller surfaces have a poorer incendivity. 

Propagating Brush Discharge The incendivity of the propagating brush discharge is so large that an ignition of dust-air mixtures with an MIE up to around 100 J must be anticipated. For dust-air mixtures, this corresponds to an EIE range of 10 to 100 J. 

Electrostatic Discharges An electrostatic discharge takes place when a gas or vapor-air mixture is stressed, electrically, to its breakdown value. Depending upon the specific circumstances, the breakdown appears as one of four types of discharges, which vary greatly in origin, appearance, duration, and incendivity. 

In order to establish safe values for velocity-diameter product, various studies have been made to determine the minimum liquid surface potential that will result in an incendive discharge in the presence of a grounded electrode. Studies reviewed in [8] showed that for credible charging conditions, liquids must be negatively charged to yield incendive bmsh discharges. The consensus has been that to avoid incendive discharges the maximum liquid... 

Arcing contacts in Division 2 areas must be installed in explosion-proof enclosures, be immersed in oil, be hermetically sealed, or be non-incendive. High-temperature devices must be installed in explosion-proof enclosures. Fuses must be enclosed in explosion-proof enclosures unless the fuses are preceded by an explosion-proof, hermetically sealed, or oil-immersed switch and the fuses are used for overcurrent protection of instrument circuits not subject to overloading in normal use. 

RP12.2 Intrinsically Siife and Non-Incendive Electrical Instruments... 

Gallery. Equipment for firing explosives into incendive mixtures of methane and air. 

Impact of an alloy containing 6% A1 and 3% Zn with rusted steel caused incendive sparks which ignited LPG-air mixtures in 11 out of 20 attempts. 

Use of a steel chisel to open a drum of carbide caused an incendive spark which ignited traces of acetylene in the drum. The non-ferrous tools normally used for this purpose should be kept free from embedded ferrous particles [1], If calcium carbide is warm when filled into drums, absorption of the nitrogen from the trapped air may enrich the oxygen content up to 28%. In this case, less than 3% of acetylene (liberated by moisture) is enough to form an explosive mixture, which may be initiated on opening the sealed drum. Other precautions are detailed [2], Use of carbon dioxide to purge carbide drums, and of brass or bronze non-sparking tools to open them are advocated [3],... 

An intimately powdered mixture, usually ignited by magnesium ribbon as a high-temperature fuse, reacts with an intense exotherm to produce molten iron and was used formerly (before the advent of gas or arc welding) in the commercial thermite welding process. Incendive particles have been produced by this reaction on impact between aluminium and rusty iron. (The term thermite reaction has now been extended to include many combinations of reducing metals and metal oxides) [1], Some accidents in demonstrating the thermite reaction are described [2],... 

Use of a rusty iron tool on an aluminium compressor piston caused incendive sparks which ignited residual propene-air mixture in the cylinder. 

Incendive discharge Any electrical discharge that has sufficient energy to ignite a specified flammable mixture. 

External causes of incendive static discharges include... 

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