حفاظت و ایمنی و استانداردهای عمومی بیمارستانی مدرس : مجتبی جهانگیرپور

Basic Electrical Safety

Electrical Safety at DCU Electrical Safety Awareness Electricity basics & few simple pointers Specific laboratory examples, A few Do’s & Don’ts & Watch out for’s January 2008 Ver 1.1

Content [ I ] Basic Electrical Theory [ Ladybird version, no maths ! ] Voltage & current Electricity in the body & effects on the body Electricity & associated hazards [ II ] Electrical Appliances Safety features, cables, connections, design General Electrical Guidelines & Precautions Electrocution [ III ] Specific Hazards & Personal Safety January 2008 Ver 1.1

[ I ] Electricity January 2008 Ver 1.1

Basic Electrical Theory Voltage [driving force] causes current [e - ] to flow AC / DC - from safety perspective - negligible difference Single Phase / Three Phase. 3 get a professional Circuit / loop is necessary for current to flow a start point - a route - an end point January 2008 Ver 1.1

Voltage, Current and Resistance Voltage increases => Current increases Resistance decreases => Current increases Voltage = Current / Resistance - Ohms Law January 2008 Ver 1.1

The complete circuit necessary for current to flow A complete Circuit or loop is necessary for current to flow January 2008 Ver 1.1

A complete circuit complete Circuit or loop is necessary for current to flow Current takes the path of least resistance January 2008 Ver 1.1

Basic Electrical Theory Voltage causes a Current to flow Water analogy A complete Circuit is necessary for current to flow Bird on HT wires January 2008 Ver 1.1

Voltages Low Tension 0 => 50V High Tension 100 => 300V Batteries: AA, AAA, MP3 player Car, trucks, busses 12 / 24 / 48 Garden lights, domestic halogen lights High Tension 100 => 300V EU Mains, Electrophoresis, DART, Capacitors SM PSUs Very High Tension 1KV + ESB pylons, TV tubes, photocopiers, X-Ray machines, Mass Spectrometers January 2008 Ver 1.1

Electricity in the body January 2008 Ver 1.1

Electricity in the body Muscles Muscles control all the body movements Including & importantly those that keep us alive - Breathing and Heart The brain controls voluntary muscles using Current pulses along nerves January 2008 Ver 1.1

Electricity in the body External current through the body causes Loss of muscle control Spasms & Involuntary movement Inability to let go Burns - external & internal January 2008 Ver 1.1

Figure 14.1 Physiological 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.

Figure 14.2 Distrubutions of perception thresholds and let-go currents These data depend on surface area of contact (moistened hand grasping AWG No. 8 copper wire). (Replotted from C. F. Dalziel, "Electric Shock," Advances in Biomedical Engineering, edited by J. H. U. Brown and J. F. Dickson IIII, 1973, 3, 223-248.)

Figure 14.3 Let-go current versus frequency Percentile values indicate variability of let-go current among individuals. Let-go currents for women are about two-thirds the values for men. (Reproduced, with permission, from C. F. Dalziel, "Electric Shock," Advances in Biomedical Engineering, edited by J. H. U. Brown and J. F. Dickson IIII, 1973, 3, 223-248.)

Figure 14. 4 Fibrillation current versus shock duration Figure 14.4 Fibrillation current versus shock duration. Thresholds for ventricular fibrillation in animals for 60 Hz ac current. Duration of current (0.2 to 5 s) and weight of animal body were varied. (From L. A. Geddes, IEEE Trans. Biomed. Eng., 1973, 20, 465-468. Copyright 1973 by the Institute of Electrical and Electronics Engineers. Reproduced with permission.)

Figure 14.5 Effect of entry points on current distribution (a) Macroshock, externally applied current spreads throughout the body. (b) Microshock, all the current applied through an intracardiac catheter flows through the heart. (From F. J. Weibell, "Electrical Safety in the Hospital," Annals of Biomedical Engineering, 1974, 2, 126-148.)

Electricity & associated hazards January 2008 Ver 1.1

Electricity - associated Hazards Indirect Injury Falls from ladder Thrown back. Fall to ground, onto sharp edge Drop objects Thermal burns – Very hot equipment surface, explosion Wires & cables - Trailing leads => trips & damage, Re-route, tidy up, cover over Life Support muscles Diaphragm and breathing Heart Fibrillation Random, uncoordinated heart contractions De-fribrillation: High voltages (3000 V at 20 A) fraction of a second Burns - death of tissue Internal [organs] External [skin] January 2008 Ver 1.1

END [ I ] Electrical Theory Section January 2008 Ver 1.1

[ II ] Electrical Appliances. Safety - design guidelines [ II ] Electrical Appliances Safety - design guidelines Connectors, cables & fuses Selection, maintenance & use Dealing with electrocution January 2008 Ver 1.1

Electrical Equipment Guidelines January 2008 Ver 1.1

Electrical Appliances Safety guiding principle “keep currents and voltages inside apparatus and away from our bodies” Inherently safe - Low voltage / low current Enclosures Insulation Safe & secure connections January 2008 Ver 1.1

[ III ] Electrical Hazards & Personal Safety January 2008 Ver 1.1

Electrocution Prevention & Training : Where are red mushroom switches ? Response: Immediately cut power, red buttons / switch / plug If in any doubt - Do not touch victim. One hand behind back, stand on insulation, tip with back of hand Use insulating rod / stick to move wires from victim. Call for assistance Talk & reassure victim If unconscious then use first aid, CPR January 2008 Ver 1.1

Electrical Hazards & Personal Safety Where Office & home 95% Laboratory 5% Trailing wires, faulty wires Mains Avoid direct working with mains. Use only low voltages (tension ) Check all leads for: Fraying, Proper clamping, Proper earthing. Repairing Do not repair, competency required One hand behind back, tip cautiously with back of hand Trust nobody, remove fuse, use phase tester Note: Switch Mode PSU, laptop chargers, CF lamps [high voltages persists on capacitors long after switch off] January 2008 Ver 1.1

Specific Hazards & Personal Safety Medical / sports equipment Very strict regulations on equipment operation, design, repair Never modify or tamper with such equipment ECG measurements. even a few micro amps in a susceptible location can have massive consequences [Basis of Heart pacemaker ] Pace makers Susceptible to strong magnetic fields [NMR! ], Possibly RF & Micro waves Solvent Flammable environments require specialised electrical equipment E.g. Fridge storage of samples stored in solvents Cold rooms / water cooling Equipment moved from a cold room with get condensation on its internal electrical circuits Avoid this movement, Use LT, give lots of time to acclimatise January 2008 Ver 1.1

Specific Hazards & Personal Safety RF & µW Capacitive coupling, no need to touch, Both can burn severely internally and externally depending on how focused. Think of them like an open air μ-wave oven HT Static, OK [Very low current, moderate power] Will jump considerable distances, beware of capacitors Power Heating effect in body => internal burns / damage Contact burns, deep burns & necrosis Trailing power and signal wires - Protect & Tidy them up January 2008 Ver 1.1

Specific Hazards & Personal Safety Other Laboratory Situations Other Office Situations Other Home Situations January 2008 Ver 1.1

Where to get more Information Your Supervisor, Manager, Head of Department Department Safety Statements Department Safety Committees & Safety Officer DCU safety - WEB Edinburgh H&S - WEB University London H&S - WEB January 2008 Ver 1.1

Live, Neutral, Earth & Fuses The Live and Neutral wires carry current around the circuit The Earth wire is there to protect you. The Earth wire can act like a back-up Neutral wire, Many appliances have metal cases e.g. kettles, toasters, dishwashers, washing machines etc. The Fuse is very thin piece of wire. The wire has a quite low melting point. As current flows through the wire it heats up. If too large a current flows it melts, thus breaking the circuit Use appropriate fuse size/rating Additional safety devices - RCDs, ELCBs, MCBs January 2008 Ver 1.1

Guidelines Use low & safe voltages EU 230 VAC / US 110 VAC Hz Select equipment appropriate for environment & use Use equipment as per manufacturer’s instruction & design Ensure adequate maintenance Insulate and enclose live parts Prevent conducting parts from becoming live. Earth, double insulation separate supply from earth, limit electric power Avoid electricity where its use could be dangerous. Rubbing, Induction & Capacitance effects can build up static electricity Toxic - Berilium heat sinking, Incomplete burning can produce carbon monoxide January 2008 Ver 1.1

Figure 14. 6 Simplified electric-power distribution for 115 V circuits Figure 14.6 Simplified electric-power distribution for 115 V circuits. Power frequency is 60 Hz.

Electrical cables & plugs Mains cable Brown Live - power Blue Neutral Green/yellow Earth January 2008 Ver 1.1

Electrical cables & plugs Mains cable Brown Live power Blue Neutral Green/yellow Earth L N January 2008 Ver 1.1

Live, Neutral, Earth & Fuses January 2008 Ver 1.1

What’s the problem? January 2008 Ver 1.1

Live, Neutral, Earth & Fuses January 2008 Ver 1.1

Figure 14.8 Macroshock due to a ground fault from hot line to equipment cases for (a) ungrounded cases and (b) grounded chassis.

Figure 14.9 Leakage-current pathways Assume 100 µA of leakage current from the power line to the instrument chassis. (a) Intact ground, and 99.8 µA flows through the ground. (b) Broken ground, and 100 µA flows through the heart. (c) Broken ground, and 100 µA flows through the heart in the opposite direction.

Figure 14.10 Thresholds of ventricular fibrillation and pump failure versus catheter area in dogs. (From O. Z. Roys, J. R. Scott, and G. C. Park, "Ventricular fibrillation and pump failure thresholds versus electrode area," IEEE Transactions on Biomedical Engineering, 1976, 23, 45-48. Reprinted with permission.)

Figure 14.11 (a) Large ground-fault current raises the potential of one ground connection to the patient. The microshock current can then flow out through a catheter connected to a different ground. (b) Equivalent circuit. Only power-system grounds are shown.

Figure 14.12 Grounding system All the receptacle grounds and conductive surfaces in the vicinity of the patient are connected to the patient-equipment grounding point. Each patient-equipment grounding point is connected to the reference grounding point that makes a single connection to the building ground.

Electrocution January 2008 Ver 1.1

Figure 14.7 Power-isolation-transformer system with a line-isolation monitor to detect ground faults.

Figure 14.13 Ground-fault circuit interrupters (a) Schematic diagram of a solid-state GFCI (three wire, two pole, 6 mA). (b) Ground-fault current versus trip time for a GFCI. [Part (a) is from C. F. Dalziel, "Electric Shock," Advances in Biomedical Engineering, edited by J. H. U. Brown and J. F. Dickson IIII, 1973, 3, 223-248.)

RCD Residual Current Device RCCB Residual Current Circuit Breaker ELCB Electric Leakage Circuit Breaker MCB Magnetic Circuit Breakers RCBO Residual Current Breaker with Overcurrent protection current difference of >30 mA for a duration of >30 ms L L N N E January 2008 Ver 1.1

CM CMRR SIG ISO Error Isolation barrier Capacitance and resistance - + Input common (a) *IMRR in v/v Output common o = IMRR ± Gain RF IMRR* ~ Isolation barrier Input control Output -V +V +o - + o = i RK RG CR3 CR1 CR2 i2 i i1 AI AII i3 RK = 1M W (c) ~ 1 2 - + (b) + 15 V DC o Power return 25 kHz - 7.5 V +ISO Out SIG ISO + 7.5 V In com In In + FB ± 5 V F.S. Oscillator Signal Mod Rect and filter Demod ± 5 V AD202 Hi Lo Isolation barrier Frequency-to- voltage converter (phase-locked loop) Osc Q ± 15 V (Receiver) ± 15 V (Driver) Isolation barrier (d) 3 pF Freq control Analog signal out, o signal in, i Figure 14.14 Electrical isolation of patient leads to biopotential amplifiers (a) General model for an isolation amplifier. (b) Transformer isolation amplifier (Courtesy of Analog Devices, Inc., AD202). (c) Simplified equivalent circuit for an optical isolator (Copyright (c) 1989 Burr-Brown Corporation. Burr Brown ISO100) (d) Capacitively coupled isolation amplifier (Horowitz and Hill, Art of Electronics, Cambridge Univ. Press. Burr Brown ISO106).

4 cm Clear plastic To patient Saline Flush valve IV tubing Gel Silicon chip Electrical cable Figure 14.15 Isolation in a disposable blood-pressure sensor. Disposable blood pressure sensors are made of clear plastic so air bubbles are easily seen. Saline flows from an intravenous (IV) bag through the clear IV tubing and the sensor to the patient. This flushes blood out of the tip of the indwelling catheter to prevent clotting. A lever can open or close the flush valve. The silicon chip has a silicon diaphragm with a four-resistor Wheatstone bridge diffused into it. Its electrical connections are protected from the saline by a compliant silicone elastomer gel, which also provides electrical isolation. This prevents electric shock from the sensor to the patient and prevents destructive currents during defibrillation from the patient to the silicon chip.

Figure 14.17 Ground-pin-to-chassis resistance test

Figure 14. 18 (a) Chassis leakage-current test Figure 14.18 (a) Chassis leakage-current test. (b) Current –meter circuit to be used for measuring leakage current. It has an input impedance of 1 k and a frequency characteristic that is flat to 1 kHz, drops at the rate of 20 dB/decade to 100 kHz, and then remains flat to 1 MHz or higher. (Reprinted with permission from NFPA 99-1996, "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association, on the referenced subject, which is represented only by the standard in its entirety.) Appliance power switch (use both OFF and ON positions) To exposed conductive surface or if none, then 10 by 20 cm metal foil in contact with the exposed surface Insulating surface Current meter I Test circuit Input of test load Leakage current being measured 1400 W 100 Millivoltmeter 15 0.10 F 900 Open switch for appliances not intended to contact a patient Grounding-contact switch (use in OPEN position) Polarity- reversing switch (use both positions) Appliance H (black) H 120 V N N (white) G G (green) Building ground H = hot N = neutral (grounded) G = grounding conductor This connection is at service I < 500 A for facility Ð owned housekeeping and maintenance appliances entrance or on I > 300 A for appliances intended for use in the patient vicinity supply side of separately derived system (a) mV (b)

Figure 14.19 Test for leakage current from patient leads to ground (Reprinted with permission from NFPA 99-1996, "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association , on the referenced subject, which is represented only by the standard in its entirety.)

Figure 14.20 Test for leakage current between patient leads (Reprinted with permission from NFPA 99-1996, "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association , on the referenced subject, which is represented only by the standard in its entirety.)

Figure 14.21 Test for ac isolation current (Reprinted with permission from NFPA 99-1996, "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association , on the referenced subject, which is represented only by the standard in its entirety.)

Figure 14.16 Three-LED receptacle tester Ordinary silicon diodes prevent damaging reverse-LED currents, and resistors limit current. The LEDs are ON for line voltages from about 20 V rms to greater than 240 V rms, so these devices should not be used to measure line voltage.

Classes and types of medical electrical equipment

Class I equipment Class I equipment has a protective earth. The basic means of protection is the insulation between live parts and exposed conductive parts such as the metal enclosure. In the event of a fault that would otherwise cause an exposed conductive part to become live, the supplementary protection (i.e. the protective earth) comes into effect. A large fault current flows from the mains part to earth via the protective earth conductor, which causes a protective device (usually a fuse) in the mains circuit to disconnect the equipment from the supply.

Class III equipment Class III equipment is defined in some equipment standards as that in which protection against electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are present. SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V dc. Proof defibrillator

Class III equipment Class III equipment is defined in some equipment standards as that in which protection against electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are present. SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V dc. Proof defibrillator

Table shows the symbols and definitions for each type classification of medical electrical equipment.

دستگاه هاي پزشكي را مي توان به 3 نوع ديگر نيز تقسيم كرد: نوعB اين نوع دستگاه هاي پزشكي مي توانند از كلاس 1، 2 يا 3 باشند. در اين دستگاه‌ها با توجه به قابليت اطمينان و جريان نشتي، حفاظت كافي در برابر شوك الكتريكي وجود دارد. اين دستگاه ها براي استفاده خارجي و داخلي جز در موارد كاتتريزاسيون مناسب هستند. نوعBF ‌اين تجهيزات داراي اجزاي آويزان شده هستند. اين اجزا براي ارتباط با پوست بيمار هستند ولي مدار داخلي شناور دارند. نوع CFاين نوع تجهيزات مربوط به ارتباط مستقيم با قلب بوده و درجه بالاي حفاظتي دارند. حداقل مقاومت بين منابع و زمين 20 مگا اهم و بين منابع و قسمت متصل شده به بيمار 70 مگا اهم است. ‌در طراحي تجهيزات پزشكي بايد موارد زير را در نظر گرفت: سيم زمين بايد قابل اطمينان باشد. بين پريزها و بدنه دستگاه بايد سيم با مقاومت پايين داشته باشد. جريان نشتي بايد كاهش داده شود.