Electric shock hazard

An additional benefit of intrinsically safe systems is the reduction of electrical shock hazards. It is cautioned, however, that intrinsically safe systems are not necessarily tested specifically for personnel shock hazards. 

Because the output of these bridges is in the range of millivolts, the cables utilized to carry the signal are normally shielded with a braided or foil-lined sheath around individual wires. The shield, as a rule, is connected to the amplifier, but never touches the actual instrumented equipment (i.e., tablet press). If this rule is violated, a ground loop may generate electrical noise and present a dangerous electrical shock hazard. 

Hence an earth leakage circuit breaker should be used in the MCC to protect the circuit against electric shock hazard. 

Worked Example for the Calculation of Earthing Current and Electric Shock Hazard Potential Difference in a Rod and Grid Earthing System... 

EARTHING CURRENT AND ELECTRIC SHOCK HAZARD POTENTIAL DIFFERENCE... 

EARTHING CURRENT AND ELECTRIC SHOCK HAZARD POTENTIAL DIFFERENCE Calculate the constants Kfi, Ka and for nse in eqnation 68 from IEEE80. 

Dalziel, C. F., 1972, Electric shock hazard, IEEE Spectr. 9 41-50 (Fehruary). 

It is important for the clinical engineer to understand fully how standards are developed, how they are used, and most importantly, how they affect the entire spectrum of health-related matters. Standards exist that address systems (protection of the electrical power distribution system from faults), individuals (means to reduce potential electric shock hazards), and protection of the environment (disposal of deleterious waste substances). 

Electric shock hazard is particularly a concern in clinical biopotential monitoring where the patient may be in a vulnerable state of health. Bioelectrodes are desirably low-resistance connections to the body for amplifier performance reasons. As discussed earlier, they similarly can offer a low-resistance pathway to ground for electric fault currents. 

At construction sites, the most common electrical hazard is the grovmd fault electrical shock. The OSHA electrical rules reqrure employers to provide either (1) grormd fardt circuit interrupters (GFCIs) for receptacle outlets, or (2) an assraed equipment grormd-ing conductor program. Either method can eliminate grormd fault electric shock hazards. 

OSHA s inspection revealed that employees were exposed to electric shock hazards due to working near an overhead powerline, using damaged/repaired extension cords, and improper construction of electrical cords. 

Employers must make sure that each affected employee uses protective footwear when working in areas where there is a danger of foot injuries due to falling or rolling objects, or objects piercing the sole, or when the use of protective footwear will protect the affected employee from an electrical hazard, such as a static-discharge or electric-shock hazard, that remains after the employer takes other necessary protective measures. 

For construction, OSHA has a focused inspection initiative, where the inspector may ask to see yoru I2P2 to determine if it meets 1926.20, and whether it s effective. If it is, the inspector won t inspect the whole jobsite, just a representative portion of it, and he/she will limit the scope of the inspection to just foru things — fall, struck-by, caught-in-or-between, and electrical-shock hazards. If there s no I2P2 or it s not effective, the visit may turn into a comprehensive inspection. 

In addition to revising the Electric Power Generation, Transmission, and Distribution, and the Electrical Protective Equipment standards, OSHA also revised the General Industry Foot Protection standard to clarify that an employer must ensure that workers use protective footwear as a supplementary form of protection when the use of protective footwear will protect the workers from electrical hazards, such as static-discharge or electric-shock hazards, that remain after the employer takes other necessary protective measures. 

As outlined previously in this chapter, the primary purpose of grounding electronic hardware is to prevent electric shock hazard. The National Electrical Code (NEC) and local building codes are designed to provide for the safety of the workplace. Local codes should always be followed. Occasionally, code sections are open to some interpretation. When in doubt, consult a field inspector. Codes constantly are being changed or... 

High-voltage power supply (e.g., Stanford Research Systems, Inc., Sunnyvale, CA, USA). VCAUTION Electric shock hazard. Please make sure that all electric connections are properly shielded. 

Suitable for liner movement Wide speed range High horsepower output High degree of reliability No electric shock hazard Low maintenance... 

However, the GFCI will not protect the employee from line-to-line contact hazards (such as a person holding two hot wires or a hot and a neutral wire in each hand). It does provide protection against the most common form of electrical shock hazard — the ground fault. It also provides protection against fires, overheating, and destruction of insulation on wiring. 

Danger from electricity may arise irrespective of whether it is ac or dc. Where dc is derived from ac supply the process of rectification will result in some superimposed ripple from the original ac waveform. Where this exceeds 10%, the electric shock hazard must be considered to be the same... 

Although the effect of a direct current shock is generally not as dangerous as with ac (there is no dangerous involxmtary grip phenomenon for example), it is recommended that similar precautions against shock be taken. In any case it will be recalled from section 4.4.1.2 that the dc electrical shock hazard could be similar to that of an equivalent ac voltage as a result of the amount of superimposed ripple. 

Section 9 deals with the electric shock hazard when the supply is PME and there is a potential difference between the PME terminal and the Class I metalwork bonded to it and true earth, and the precautions needed to ensure safety. It fails, however, to mention the worst case (admittedly rare) which arises from a break in the PEN conductor. 

In confined and conductive locations the potential electric shock hazard is increased and special precautions are needed. Examples of confined, conductive spaces are inside boilers and other metal vessels or inside metal pipes, flues and ducts where the area of body contact to earthed metalwork is likely to be substantial. Even if the interior is dry, the shock risk is enhanced, but if it is damp it is worse. In these circumstances the llOV system is not considered safe and pneumatic, hydraulic or battery powered tools are advocated. For lighting, battery powered cap and hand lamps could be used or the luminaires could be supplied from a safety transformer at not more... 

There are potential electric shock hazards at higher voltages from three-phase multi-operator welding and from the use of multiple power sources (see Figs 16.6 and 16.7). In these cases the operators should be separated so that no operator can touch two electrode holders at different voltages at the same time. 

Ventricular Fibrillation Because only a small amount of current is required to disrupt the natural rhythm of the heart, ventricular fibrillation is considered the most dangerous electric shock hazard. The shock current needs to pass through the heart during the phase when the ventricles are starting to relax after a contraction (Lee 1966). When fibrillation occurs, the effective pumping action of the heart ceases, the pulse disappears, and death usually occurs within minutes. The lower boundary of the threshold of ventricular fibrillation is generally considered to be 50 mA. 

Reduce electric-shock hazards to personnel caused by high frame potentials during a ground fault... 

Power supplies and electrophoresis equipment pose serious fire hazard and electrical shock hazards if not used properly. 

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