03-09-2012, 02:33 PM
Principles of Biomedical Systems & Devices
electrcal safety.ppt (Size: 2.38 MB / Downloads: 86)
Safety 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 control
Electrical 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 failure
Physiological Effects of Electricity
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.