Prevention of Electrocution

OVERVIEW

Prevention of electrocution in the hospital setting involves consideration of:

  • General measures
  • Class of Equipment
  • Type of Equipment allowed to be connected to patient
  • Equipotentiality
  • Isolating (floating) Circuits
  • Circuit breakers (RCD’s)
  • Surgical Diathermy
  • Area Classification

APPROACH

1. General measures

  • maintenance and testing
  • making sure patient isn’t in contact with earthed objects
  • anti-static shoes (high impedance -> current can’t flow through)
  • no extension cords that can reach from an unprotected area
  • no double adaptors (may not sit well and can leak current)
  • all equipment should meet Australasian Standards for Safety
  • personnel education

2. Class of Equipment

  • Class 1: third pin of plug (direct earthing) + metal casing -> this circuit should be low resistance and if live wire comes in contact with an accessible part should be linked to a fuse that breaks the circuit
  • Class 2: double or reinforced insulation (non-conductive plastic), earthing wire not needed
  • Class 3: provides protection by stepping down main power to a safety extra low voltage (SELV, see below

3. Type of Equipment allowed to be connected to patient

  • based on maximal permissible leakage currents
  • Type B: may be class 1, 2 or 3 but maximum leakage must not exceed 100microamps (thus must not be directly connected to heart)
  • Type BF: as for type B but uses a isolated (or floating circuit) -> see below
  • Type CF: these provide the highest degree of protection using isolating circuits and having a maximum current leakage of if leaves entire power susceptible to failure

4. Equipotentiality

  • connections of equipment to make them all the potential differences the same
  • connections of equipment by low impedance green cables
  • includes anaesthetic machines and IV poles with pumps on them
  • prevents devices leaking charge to a user or patient

5.  Isolating (floating) Circuits

  • patient circuit not earthed by using an isolated transformer
  • can be used to isolate an entire theatre -> if leaves entire power susceptible to failure
  • used frequently to isolate individual instruments
  • line isolation monitor attached that continuously monitors the potential for current to flow from isolated current supply to ground (alarm activated if 2mA of current detected)

6. Circuit breakers (RCD’s)

  • live and neutral wire wrapped around the core of a transformer and then around a circuit breakers (normally the magnetic fluxes cancel each other out)
  • if excess current is leaked -> magnetic field is produced between the transformer that triggers a current causing break in circuit
  • will protect against macroshock

7. Surgical Diathermy

  • the use of the heating effects of high frequency (kHz -> MHz) electrical to coagulate or cut tissue
  • can cause burning, explosions or muck up pacemakers

Monopolar diathermy

  • 200 kHz -> 6 MHz
  • neutral and active
  • neutral = large conductive area -> low current density and minimal heat
  • active = small contact area + high current density

Bipolar diathermy

  • lower power output
  • output between 2 points on forceps -> high local current density
  • no current passes through rest of body

8. Area Classification

Body protected areas

  • patients connected to equipment that lowers the natural resistance of the skin
  • examples: electrode gels, conductive fluids, metal needles and catheters
  • protection from macroshock is goal
  • RCD’s, line isolation transformers and monitors used

Cardiac protected areas

  • this is where procedures are performed within or near the heart -> protection from microshock is required
  • examples: intracardiac pacing electrodes, intracardiac ECG electrodes, intracardiac catheters
  • equipotential earthing, RCD’s and line isolation monitors used

References and Links

  • Boumphrey, S et al (2003) “Electrical Safety in the Operating Theatre” CEPD Volume 3, Number 1, pages 10-14
  • Magee et al (2005) “The physics, clinical measurement and equipment of anaesthetic practice” Electricity Chapter, page 167

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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