Electricity hazards electrical arcs

Although microwave-heated organic reactions can be smoothly conducted in open vessels, it is often of interest to work with closed systems, especially if superheating and high-pressure conditions are desired. When working under pressure it is strongly recommended to use reactors equipped with efficient temperature feedback coupled to the power control and/or to use pressure-relief devices in the reaction vessels to avoid vessel rupture. Another potential hazard is the formation of electric arcs in the cavity [2], Closed vessels can be sealed under an inert gas atmosphere to reduce the risk of explosions. 

Crannell, B. S., Eighmy, T. T., Krzanowski, J. R. Eusden, J. D. Jr. 1999. Phosphate stabilization mechanisms for heavy metals in electric arc furnace smelter dusts. In Nikolaidis, N., Erkey, C. Smets, B. (eds) Hazardous Wastes and Hazardous Materials. Technomic Publishing, Lancaster, Pennsylvania, 561-570. 

Electric arc furnace dust is a listed hazardous chemical waste. This material is deemed hazardous because it contains relatively high concentrations of heavy metals. The waste consists of the emission control dust or sludge collected from electric arc furnaces during the manufacture of iron and steel. The principle chemicals of concern and their concentrations are listed in Table 7.5 (EPA, 1988). 

Introduction to Analysis. All previous examples involved waste in which radionuclides were assumed to be the only hazardous substances. However, the contaminants of concern in electric arc furnace dust include chemicals that induce stochastic and deterministic effects. Furthermore, the deterministic chemicals affect different organs, and some affect more than one organ. 

Table 7.5—Concentrations of hazardous chemicals in untreated, high-zinc electric arc furnace dust waste.

As indicated in Table 7.6, all hazardous chemicals in electric arc furnace dust are assumed to induce deterministic responses. The possible responses include renal toxicity, effects on the cardiovascular system, dermal or ocular effects, decrease in body weight, hepatic toxicity, and respiratory toxicity. Decrease in body weight is not a response in a particular organ but is assumed to be a health effect of concern. All deterministic responses are assumed to be induced by more than one chemical in the waste. Furthermore, some of the chemicals (barium, beryllium, chromium, and lead) are assumed to induce all responses. 

Given the assumption that an acceptable stochastic risk from disposal in a hazardous waste facility is about 10 3 (see Table 7.1), the stochastic risk index due to the presence of radionuclides in the electric arc furnace waste is (2.5 X 10 5)/10 3 = 0.025. Since this result is much less than unity, the waste clearly would be classified as low-hazard due only to the presence of 137Cs, and there is no need to perform a less conservative analysis. 

This result is much less than unity. Therefore, based on the assumptions used in this analysis, the electric arc furnace waste would be classified as low-hazard. 

As in the example of electric arc furnace waste in the previous section, this result for a hazardous waste that contains heavy metals indicates the importance of an intention to maintain perpetual institutional control over hazardous waste disposal sites in allowing the waste to be classified as low-hazard. 

The example analyses for electric arc furnace dust in Section 7.1.7 and a hazardous chemical waste in Section 7.1.8 lead to an important conclusion about these particular wastes. The concentrations of heavy metals, especially lead, in the electric arc furnace waste clearly are sufficiently high that long-term exposure to the waste by an inadvertent intruder may need to be precluded in order to ensure that deterministic effects would not occur. In addition, for either waste, the stochastic risk that could result from unrestricted release of a disposal site might exceed acceptable levels, due to the concentrations of heavy metals that induce stochastic effects. Both of these factors indicate that these wastes may be classifiable as low-hazard only if perpetual control would be maintained over near-surface disposal sites to prevent long-term exposures of inadvertent intruders. Such a conclusion also was obtained in the example of uranium mill tailings discussed in Section 7.1.5. 

OSHA requires flame retardant clothing (FRC) for workers at sites based on the quantity of flammable materials (liquids, solids, and gasses) and reactive chemicals that are handled and/or processed with activities at a facility. Both OSHA and NFPA 2113 see the need for FRC if 1) flash fire hazards exist on a continuous basis in various site areas and 2) when employees such as operators and maintenance personnel are in the areas where flash fire hazards exist. FRC can significantly reduce a bum injury by giving the wearer precious escape time from an ignition source and can greatly increase the chance for survival if the wearer is caught in a flash fire or electric arc. 

Workers in the energy and electrical sectors have many different and sometimes conflicting needs for protection. In Canada alone, approximately 500,000 workers are employed in the oil and gas industries. Despite strict safety protocols, the potential for explosions, flash fires, and/or electrical arc is always present. Although individual workers may never experience such hazards over the course of their working life, they normally wear PPE, including protective clothing, as a precautionary measure. Again, the presence of moisture in the form of steam or hot water is an additional hazard for these workers (Fig. 9.1). 

Hoagland H. Flame resistant textiles for electric arc flash hazards. In Kihnc FS, editor. Handbook of fire resistant textiles. Oxford Woodhead Publishing 2013. p. 549-80. 

The approach limit at a distance from a prospective arc source or arc flash hazard within which an individual could receive a second-degree burn if an electrical arc flash incident occurs. 

Working around electrical equipment can expose employees to many hazards. One of most dangerous hazards is the arc burn, which results from an electric arc flash and the accompanying arc blast. 

Estimate of available heat energy. For each employee exposed to hazards from electric arcs, the employer shall make a reasonable estimate of the incident heat energy to which the employee would be exposed. 

Prohibited clothing. The employer shall ensure that each employee who Is exposed to hazards from flames or electric arcs does not wear clothing that could melt onto his or her skin or that could Ignite and continue to burn when exposed to flames or the heat energy estimated under paragraph (g)(2) of this section. 

Paragraph (g)(1) of 1926.960 requires the employer to assess the worl lace to identify employees exposed to hazards from flames or from electric arcs. This provision ensures that the employer evaluates employee exposure to flames and electric arcs so that employees who face such exposures receive the required protection. The employer must conduct an assessment for each... 

Flame-resistant clothing includes clothing that is inherently flame resistant and clothing chemically treated with aflame retardant. (See ASTM FI 506-1 Oa, Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, and ASTM FI 891-12 Standard Specification for Arc and Flame Resistant Rainwear.)... 

Probability that an electric arc will occur. Identify employees exposed to electric-arc hazards. The Occupational Safety and Health Administration will consider an employee exposed to electric-arc hazards if there is a reasonable likelihood that an electric arc will occur in the employee s work area, in other words, if the probability of such an event Is higher than it is for the normal operation of enclosed equipment. Factors to consider include ... 

Task Is employee exposed to flame or electric-arc hazard ... 

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