1. حفاظت و ایمنی و استانداردهای عمومی بیمارستانی
مدرس :
مجتبی جهانگیرپور

5. Basic Electrical Safety

6. 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 Ver 1.1

7. 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 Ver 1.1

8. [ I ] Electricity
January Ver 1.1

9. Basic Electrical Theory
Voltage [driving force] causes current [e - ] to flow
AC / DC - from safety perspective - negligible difference
Single Phase / Three Phase  get a professional
Circuit / loop is necessary for current to flow
a start point - a route - an end point
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10. Voltage, Current and Resistance
Voltage increases => Current increases
Resistance decreases => Current increases
Voltage = Current / Resistance Ohms Law
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11. The complete circuit necessary for current to flow
A complete Circuit or loop is
necessary for current to flow
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12. A complete circuit complete Circuit or loop
is necessary for current to flow
Current takes the path of least resistance
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13. Basic Electrical Theory
Voltage causes a Current to flow
Water analogy
A complete Circuit is necessary for current to flow
Bird on HT wires
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14. 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 => 300V
EU Mains, Electrophoresis, DART, Capacitors SM PSUs
Very High Tension 1KV +
ESB pylons, TV tubes, photocopiers, X-Ray machines, Mass Spectrometers
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16. Electricity in the body
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17. 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
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18. Electricity in the body
External current through the body causes
Loss of muscle control
Spasms & Involuntary movement
Inability to let go
Burns - external & internal
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19. 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.

20. 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, )

22. Figure 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, )

23. Figure 14. 4 Fibrillation current versus shock duration
Figure 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, Copyright 1973 by the Institute of Electrical and Electronics Engineers. Reproduced with permission.)

24. 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, )

27. Electricity & associated hazards
January Ver 1.1

28. 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]
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29. END [ I ] Electrical Theory Section
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30. [ II ] Electrical Appliances. Safety - design guidelines
[ II ] Electrical Appliances Safety - design guidelines Connectors, cables & fuses Selection, maintenance & use Dealing with electrocution
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31. Electrical Equipment Guidelines
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32. 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
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34. [ III ] Electrical Hazards & Personal Safety
January Ver 1.1

35. 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 Ver 1.1

36. 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 Ver 1.1

37. 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
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38. 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
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39. Specific Hazards & Personal Safety
Other Laboratory Situations
Other Office Situations
Other Home Situations
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40. 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 Ver 1.1

41. 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 Ver 1.1

42. 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 Ver 1.1

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

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

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

46. Live, Neutral, Earth & Fuses
January Ver 1.1

47. What’s the problem?
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48. Live, Neutral, Earth & Fuses
January Ver 1.1

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

52. 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.

53. Figure 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, Reprinted with permission.)

54. Figure (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.

55. Figure 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.

61. Electrocution
January Ver 1.1

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

65. Figure 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, )

66. 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 Ver 1.1

72. 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 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).

73. 4 cm Clear plastic To patient Saline Flush valve IV tubing Gel
Silicon chip
Electrical cable
Figure 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.

77. Figure 14.17 Ground-pin-to-chassis resistance test

79. Figure 14. 18 (a) Chassis leakage-current test
Figure (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 , "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 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 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
< A for facility Ð
owned housekeeping and maintenance appliances
entrance or on I
> A for appliances intended for use in the patient vicinity
supply side of
separately derived
system
(a) mV
(b)

81. Figure Test for leakage current from patient leads to ground (Reprinted with permission from NFPA , "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 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.)

83. Figure Test for leakage current between patient leads (Reprinted with permission from NFPA , "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 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.)

85. Figure Test for ac isolation current (Reprinted with permission from NFPA , "Health Care Facilities," Copyright © 1996, National Fire Protection Association, Quincy, MA 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.)

87. Figure 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.

88. Classes and types of medical electrical equipment

90. 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.

92. 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

94. 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

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

97. 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.