Ignition sources static electricity

Handle flammable substances only in areas Ifee of ignition sources. Besides open flames, ignition sources include electrical equipment (especially motors), static electricity, and, for some materials (e.g., carbon disulfide), even hot surfaces. Check the work area for flames or ignition sources before using a flammable substance. Before igniting a flame, check for the presence of a flammable substance. 

While with-in the mobile x-ray system, the waste in the sampler, is contained within a replaceable (and disposable) polyvinyl chloride (PVC) sleeve with a wall thickness of approximately 0.2-inches and a sealed bottom. It was anticipated that the PVC tube or sleeve would, with use, become highly contaminated with waste residues which drip of fall-off the sampler. The sleeve is coated with a conductive coating to prevent static electricity buildup . There are no sources of ignition in this sealed spare. The sampler (and waste) is coupling which includes a positive pressure gasket. This barrier is further isolated by a second barrier consisting of an epoxy coated aluminum sleeve also sealed-off from the main x-ray cabinet and PVC sleeve. There are also no potential sources of ignition in this isolated secondary space as well. 

In order for static electricity to be a source of ignition, four conditions must be fulfilled... 

It is recommended that flammability always be assessed first, since it is inherently safer to avoid flammable atmospheres than to avoid sources of ignition such as static electricity. If a flammable atmosphere cannot be avoided at all times, the system should be designed to minimize both the probability and consequences of ignition. In this chapter it is assumed that static electricity is the only source of ignition however, in practical situations all sources of ignition such as those described in [ 157] should be evaluated. 

Equipment Failures Safety system Ignition Sources Furnaces, Flares, Incinerators, Vehicles, Electrical switches. Static electricity, Hot surfaces. Cigarettes Human Failures Omission, Commission, Fault diagnosis. Decisions Domino Effects Other containment failures. Other material release External Conditions Meteorology, Visibility... 

Static electricity (static for short) has been blamed for many fires and explosions, sometimes con ectly. Sometimes, however, investigators have failed to find any other source of ignition. So they assume that it must have been static even though they are unable to show precisely how a static charge could have been formed and discharged. 

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... 

Ignition in 23% of the cases where this occurred, the source was unknown in about a third of the incidents in which the source was known, it was auto-ignition. Other common sources were flames, hot surfaces, sparks, lighming, static electricity and electrical equipment. In many cases conditions changed after a permit-to-work had been issued (see Section 1.3.2). 

These can be readily ignited by flames, sparks, static electrical discharges (often the most likely), hot surfaces, and many other sources. Table 7-31 lists dust cloud ignition temperatures ranging from 572°F to 1112° F, and can be contrasted to flammable vapor-air ignition temperatures from 428° F to 1170°F. Generally, ignition tempera-... 

A common ignition source within chemical plants is sparks resulting from static charge buildup and sudden discharge. Static electricity is perhaps the most elusive of ignition sources. Despite considerable efforts, serious explosions and tires caused by static ignition continue to plague the chemical process industry. 

Ignition arises from a wide variety of sources, including static electricity, hot surfaces, sparks, open flames, and electric circuits. Ignition sources are elusive and difficult to eliminate entirely, although efforts should always be made to reduce them. 

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