Rowan ECE 09.404 - Lecture 20- 21 Electrical Safety

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Slide 1This Week in PBS&DSafety in Clinical EnvironmentElectrical SafetyPhysiological Effects of ElectricitySlide 6Slide 7Important Susceptibility ParametersSlide 9Slide 10Slide 11Slide 12Distribution of Electrical PowerDistribution of PowerGROUND!Isolated Power DistributionMacroshockMacroshock HazardsSlide 19Microshock HazardsSlide 21Microshock via Ground PotentialsMicroshock Via Ground PotentialsSafety Codes & StandardsBasic Approaches to Shock ProtectionGrounding SystemsIsolated Power SystemsGround – Fault Circuit Interrupters (GFCI)GFCIProtection through Equipment DesignElectrical IsolationTransformer Isolation AmplifiersOptical Isolation AmplifierElectrical Safety Analyzers Wiring / Receptacle TestingElectrical Safety Analyzers Testing Electrical AppliancesSlide 36Slide 37Leakage current TestersLeakage Current testersLeakage Current TestersPrinciples of Biomedical Systems & DevicesPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Principles of Biomedical Systems & DevicesLecture 20- 21 Electrical SafetyPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404This Week in PBS&DSafety in the clinical environment: Electrical safetyPhysiological effects of electricitySusceptibility parametersDistribution of electrical powerIsolated power systemsMacroshock hazardsMicroshock hazardsElectrical safety codes and standardsProtectionPower distributionGround fault circuit interrupters (GFCI)Equipment designElectrical safety analyzers / Testing electrical systemsPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Safety in Clinical EnvironmentElectrical hazardsElectrical shocks (micro and macro) due to equipment failure, failure of power delivery systems, ground failures, burns, fire, etc.Mechanical hazards mobility aids, transfer devices, prosthetic devices, mechanical assist devices, patient support devicesEnvironmental hazardsSolid wastes, noise, utilities (natural gas), building structures, etc.Biological hazardsInfection control, viral outbreak, isolation, decontamination, sterilization, waste disposal issuesRadiation hazardsUse of radioactive materials, radiation devices (MRI, CT, PET), exposure controlPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Electrical SafetyMany sources of energy, potentially hazardous substances, instruments and proceduresUse of fire, compressed air, water, chemicals, drugs, microorganisms, waste, sound, electricity, radiation, natural and unnatural disaster, negligence, sources of radiation, etc. Medical procedures expose patients to increased risks of hazards due to skin and membranes being penetrated / altered10,000 device related injuries in the US every year! Typically due to Improper useInadequate trainingLack of experienceImproper (lack of) use of manualsDevice failurePBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Physiological Effects of ElectricityFor electricity to have an effect on the human body:An electrical potential difference must be presentThe individual must be part of the electrical circuit, that is, a current must enter the body at one point and leave it at another.However, what causes the physiological effect is NOT voltage, but rather CURRENT.A high voltage (K.103V) applied over a large impedance (rough skin) may not cause much (any) damageA low voltage applied over very small impedances (heart tissue) may cause grave consequences (ventricular fibrillation)The magnitude of the current is simply the applied voltage divided by the total effective impedance the current faces; skin : largest.Electricity can have one of three effects:Electrical stimulation of excitable tissue (muscles, nerve)Resistive heating of tissueElectrical burns / tissue damage for direct current and high voltagesPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Physiological Effects of ElectricityPhysiological effects of electricity. Threshold or estimated mean values are given for each effect in a 70 kg human for a 1 to 3 s exposure to 60 Hz current applied via copper wires grasped by the hands.Dry skin impedance:93 kΩ / cm2Electrode gel on skin: 10.8 kΩ / cm2Penetrated skin: 200 Ω / cm2The real physiological effect depends on the actual path of the currentPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Threshold of perception: The minimal current that an individual can detect. For AC (with wet hands) can be as small as 0.5 mA at 60 Hz. For DC, 2 ~10 mALet-go current: The maximal current at which the subject can voluntarily withdraw. 6 ~ 100 mA, at which involuntary muscle contractions, reflex withdrawals, secondary physical effects (falling, hitting head) may also occurRespiratory Paralysis / Pain / Fatigue At as low as 20 mA, involuntary contractions of respiratory muscles can cause asphyxiation / respiratory arrest, if the current is not interrupted. Strong involuntary contraction of other muscles can cause pain and fatigueVentricular fibrillation 75 ~ 400 mA can cause heart muscles to contract uncontrollably, altering the normal propagation of the electrical activity of the heart. HR can raise up to 300 bpm, rapid, disorganized and too high to pump any meaningful amount of blood  ventricular fibrillation. Normal rhythm can only return using a defibrillatorSustained myocardial contraction / Burns and physical injury At 1 ~6 A, the entire heart muscle contracts and heart stops beating. This will not cause irreversible tissue damage, however, as normal rhythm will return once the current is removed. At or after 10A, however, burns can occur, particularly at points of entry and exit.Physiological Effects of ElectricityPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Important Susceptibility ParametersThreshold and let-go current variabilityDistributions of perception thresholds and let-go currents These data depend on surface area of contact, moistened hand grasping AWG No. 8 copper wire, 70 kg human, 60Hz, 1~3 s. of exposurePBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Important Susceptibility ParametersFrequencyNote that the minimal let-go current


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Rowan ECE 09.404 - Lecture 20- 21 Electrical Safety

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