Static sparks

Even if a static spark ignites a mixture of flammable vapor and air, it is not really correct to say that static electricity caused the fire or explosion. The real cause was the leak or whatever event led to the formation of a flammable mixture. Once flammable mixtures are formed, experience shows that sources of ignition are likely to turn up. The deliberate formation of flammable mixtures should never be allowed except when the risk... 

Section 5.4.1 described explosions in storage tanks, and Section 13.3 described explosions in tank trucks, ignited by static sparks. The static was formed by the flow of a nonconducting liquid, and the spark discharges occurred between the body of the liquid and the grounded metal containers (or filling arms). 

Ignition can take place for any flammable mixture within the concentration ranges for the respective LEL and UEL. The conditions for ignition may vary with the specific mixture, the type of oxidant (usually air or pure oxygen), the temperature, and pressure of the system. Ignition may result from electrical spark, static spark, contact with hot surfaces (autoignition) (see Figures 7-48,... 

Eizember, R. F. et al., J. Org. Chem., 1974, 39, 1792-1793 During oven-drying, kg quantities of the salt exploded violently. Investigation showed that self-propagating and extremely rapid decomposition of a cold sample can be initiated by local heating to over 200° C by a flint spark, prolonged static spark or flame. The sodium salt could only be initiated by flame, and the free acid is much less sensitive. 

It explodes violently on slow heating to 250°C and can be initiated by static sparks, but not apparently by impact. 

Chlorine gas, produced by electrolysis of brine, was dried by passage through a mist of sulfuric acid in a drying tower, where static charge was generated. An explosion in the tower, (presumably involving hydrogen as fuel) was attributed to initiation by static spark. 

Although the massive metal is relatively inert, when powdered it becomes very reactive. The dry powder may react explosively at elevated temperatures with nitrogen, phosphorus, oxygen, sulfur and other non-metals. The halogens react similarly, and in contact with hot cone, nitric acid and other oxidants it may explode (often after a delay with nitric acid). The powder is pyrophoric and readily ignitable by friction, heat or static sparks, and if dry bums fiercely. Presence of... 

H. Deichelmann, The Electrostatic Charge of Glass-Lined Vessels and Piping, Pfaudler PWAG Report 326e. J.S. Dorsey, Static Sparks How to Exorcise the Go Devils, Chemical Engineering (Sept. 13,1976), pp. 203 -205. 

The accident investigation indicated that the explosion was caused by a static spark that jumped from the steel nozzle to the tank car. The nozzle was not bonded to the tank car to prevent static accumulation. The use of a nonmetallic hose probably also contributed. 

Most hydrocarbon vapors have an MIE of about 0.25 mj. This is very low—a static spark that you can feel is greater than about 20 mj. Dusts typically have MIEs of about 10 mj. In both the vapor and dust cases, wide variability in the values is expected. 

Reddy, G. O. et al Thermochim. Acta, 1983, 66, 231-244 Of the four salts with Hg2+, Pb2+, Ba2+ and 2Na+, the thermal sensitivity and impact-, friction- and static spark-sensitivities decreased in that order, as expected. These and other entries are ... 

One must also keep in mind that these experiments are measuring the temperature sensitivity of a particular composition, in which the entire sample is heated to the experimental temperature. Ignition sensitivity can also be discussed in terms of the relative ease of ignition due to other types of potential stimuli, including static spark, impact, friction, and flame. 

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