Dust ignition

The dust-ignition-proof protection concept excludes dust from entering the device enclosure and will not permit arcs, sparks, or heat generated by the device to cause ignition of external suspensions or accumulations of the dust. Enclosure requirements can be found in ANSI/UL 1203-1994, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous Locations. ... 

UL 1203 plosion-proof and Dust-ignition-proof Electrical Equip-nt for Use in Hazardous Locations... 

NOTE Refer all explosion-proof and dust ignition-proof applications greater than 3,300 ft altitude to the factory. 

FPN) Dust-ignitionproof equipment is defined in Section 502-1. For further information, see Explosionproof and Dust-Ignition-proof Electrical Equipment for Use in Hazardous (Classified) Locations, ANSI/UL 1203-1988. 

A dust-ignition-proof machine is a totally enclosed machine whose enclosure is designed and constructed in a manner which will exclude ignitable amounts of dust or amounts which might affect performance or rating, and which will not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specific dust on or in the vicinity of the enclosure. 

Sodium and potassium react explosively (the latter more violently), and zinc dust ignites, all in contact with the liquid bromide. 

Zinc dust ignites in contact with a little phosphoryl chloride, and subsequent addition of water liberates phosphine which ignites. 

Addition of water to an intimate mixture of zinc powder and the salts causes spontaneous ignition [1], and a mixture of ammonium nitrate and ammonium chloride (9 1) sprinkled with zinc dust ignites vigorously when moistened [2], Premature spontaneous ignition of the mixture was attributed to absorption of moisture by the hygroscopic salt mixture [3],... 

For a dust ignition to occur, the suspended solids concentration must lie between lower and upper limits which vary from material to material and are influenced by subtle factors such as particle shape and size distribution. From the standpoint of assessing safety hazards in commercial and industrial operations, the lower explosive limit is the more important one. The rationale of this statement is that, if the possibility of exceeding the lower limit in a powder-handling operation can not be completely ruled out, then a hazard must be recognized and appropriate measures taken. Over the... 

Types of dust Ignition temp, of dust cloud, °C Ignition temp, of dust layer, °C Min. ignition energy (MIE), J Min. explosion cone., g/nC... 

An electrostatic dust ignition can occur when the discharge releases sufficient thermal energy within a sufficiently short period of time and small volume to ignite the suspended dust. Electrostatic ignition is complicated by the fact that there are a number of distinct ESD mechanisms important in electrostatic hazards and hazard abatement (Glor, 1988). 

Figure 5. The capacitive discharge. Sometimes series resistance slows the discharge, increasing or decreasing the likelihood of a dust ignition.

Two other useful parameters related to capacitive sparks and dust ignitions are (i) the optimum sparking distance is 10 mm and (ii) the quenching distance is 7 mm. Refer to Sec. 4.1 and Table 5, where MIE is discussed in more detail. 

Comparable equipment suitable for use in Class II, Division 1 locations is called dust-ignition proof. Dust-tight equipment is designed for use in Class II, Division 2 locations. These terms should not be confused with equipment designated "dustproof." Dustproof equipment is constructed or protected so that dust will not interfere with its successful operation. This term does not imply the equipment is suitable for use in a hazardous (classified) area. 

References, brief abstracts when available, to studies of firedamp and/or coal dust ignitions explosions, not listed in previous Encyclopedia Vols are given below ... 

It is categorically assumed that dusts ignited in the laboratory by a spark source are an explosive hazard in the industry. However, some dusts that do ignite with a spark source are also shown to present a hazard by the Godbert-Greenwald furnace test and by experience... 

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