Dust, combustible ignition temperature

Many combustible dusts produced by industrial processes are explosible when they are suspended as a cloud in air. A spark may be sufficient to ignite them. After ignition, flame spreads rapidly through the dust cloud as successive layers are heated to ignition temperature. 

Extinguishing Agents Dry chemical, carbon dioxide, water fog, chemical foam Fire Extinguishing Agents Not To Be Used None Special Hazards of Combustion Products Not pertinent Behavior in Fire Vapor from molten benzoic acid may form explosive mixture with air. Concentrated dust may form explosive mixture in air Ignition Temperature (deg. F) 1,063 Electrical Hazard Not pertinent Burning Rate Not pertinent. 

Fire Hazards - Flash Point (deg. F) 350 OC Flammable Limits in Air (%) Not pertinent Fire Extinguishing Agents Water, foam, dry chemical, or carbon dioxide Fire Extinguishing Agents Not To Be Used No data Special Hazards of Combustion Products No data Behavior in Fire Dust explosion is high probability Ignition Temperature No data Electrical Hazard No data Burning Rate Not pertinent. 

Equipment shall be approved not only for the class of location but also for the explosive, combustible, or ignitable properties of the specific gas, vapor, dust, fiber, or flyings that will be present. In addition. Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in Section 500-3(1). Class III equipment shall not exceed the maximum surface temperatures specified in Section 503-1. 

Fuel treatments have been used for very many years as an aid to improving the combustion efficiency process. Old formulations often used saw dust, wood flour, common salt, zinc sludge, ground oyster shell, and similar crude ingredients, but could still provide a dramatic effect when thrown into a fire. The metallic salts present (sodium in salt, zinc in sludge, and calcium in shell) acted as catalysts that dramatically lowered the ignition temperature of soot deposits from around 1100 °F/590 °C to only 600 °C/315 °C the fire burned vigorously and the soot disappeared. 

The lower explosive limit and minimum explosive concentrations of flax, wool, cotton, jute, hemp and sisal fibres are of the same order of magnitude as those of highly explosive dusts [15], The explosibility of pyrites dusts with sulfur contents above 20% was evaluated experimentally. Dusts of 30% sulfur content gave explosion pressures of 3 bar at pressure rise rates of 16 bar/sec. Mixtures of 60% pyrites and 40% powdered limestone still showed significant pressure effects, and the proportion of limestone actually needed to suppress explosions was considerably above the values currently accepted by mining industries [16], Effects of mixtures of particle sizes in combustible dusts upon minimum ignition temperature (T ") and upon presence or absence of explosion were studied. Presence of 30% of fines in a coarse dust lowers Tf significantly [17], Experimental explosions of polyethylene,... 

The MIE of gas — air or vapour—air mixtures can be determined from the structural formula and the molar heat of combustion of the compounds studied, and equations for the calculation are presented. The method is stated to give more accurate results than conventional methods used to assess flammability of mixtures of gas or vapour with air [1], It is claimed that in oxygen MIEs are about a hundredfold lower than in air [2], A study of the ignition behaviour of dusts, including correlation of electrical and mechanical minimum ignition spark energies and ignition temperature is made [3],... 

Hazards of Combustion Products. Data not available Behavior in Fire Melts and may decompose to give volatile acetic vapors pf valeric acid and other substances. Dust may form explosive mixture with air Ignition Temperature (deg. F) 788 Electrical Hazard. Not pertinent Burning Rate. Not pertinent. Chemical Reactivity Reactivity with Water No reaction Reactivity with Common Materials Data not available Stability During Transport Stable Neutralizing Agents for Acids and Caustics Rinse with dilute sodium bicarbonate or soda ash solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Grain dust collects in the warehouse. The dust reacts with oxygen of the air. This reaction generates heat. The heat raises the temperature to ignition temperature and spontaneous combustion takes place. Sometimes, grain warehouse fires are caused by sparks. 

The dust from the hay collects in the bam. The dust reacts with oxygen. The reaction generates heat which raises the temperature to ignition temperature. Spontaneous combustion occurs. When a haystack catches fire outdoors, the heat is liberated well inside the haystack. The heat is generated by the action of bacteria that decompose the hay. The heat released by this starts a fire. 

Many combustible dusts produced by industrial processes are explosible when they are suspended as a cloud in air. Even a spark may be sufficient to ignite them. After ignition, flame spreads rapidly through the dust cloud as successive layers are heated to ignition temperature. The hot gases expand and produce pressure waves that travel ahead of the flame. Any dust lying on surfaces in the path of the pressure waves will be thrown into the air and could cause a secondary explosion more violent and extensive than the first. 

Table 1.4 Ignition temperatures T, and glow temperatures TG for combustible dusts in air with a pressure of 1.013 105Pa. TG refers to a layer thickness of 5 mm...

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