Advertisement
Articles
Advertisement

How to solve the problem of excessive leakage current in the healthcare industry

Thu, 10/11/2012 - 12:52pm
Lennart Elmlund, Director of Marketing, Bridgeport Magnetics Group

The 2012 Edition of NFPA 99 Healthcare Facilities Code reflects the new format of using a risk-based approach for determining the level of protection.   An example is the definition of wet locations. The new code, in absence of any government regulations, gives the responsibility to the governing body of the healthcare organization to designate wet procedure locations.  

Leakage current became a concern in the healthcare community more than 50 years ago, when cardiovascular medicine and surgery began invading the heart with electrical and electromechanical probes.  The 2012 edition now uses the term “touch current” instead of leakage current to be consistent with the International Electrotechnical Commission (IEC) and other standard bodies.  Chassis touch current is the leakage current that flows from the medical device chassis and its parts while in normal operation, excluding patient connections, to any person (staff or patient) touching these devices.  The leakage current flows through that person to earth or to another part of the equipment chassis or to some other earth-grounded chassis.

For cord connected equipment in operating rooms and patient care vicinities, the maximum touch (leakage) current must not exceed 100 microamperes with the ground wire intact and 500 microamperes with ground wire disconnected.

Excessive touch current may be life-threatening to the patient if a staff member is touching the equipment with one hand and simultaneously touches the patient’s bed with the other hand. The intensity of the shock depends on how much current is transmitted through the person’s body.  The threshold of perception for an average built adult is one mA or milliampere (1000 microamperes) of current which would generate a slight tingling feeling through the fingertips. Cardiac arrest happens at 5 milliamperes (5,000 microamperes) leakage current.

Unfortunately, outside the Biomed and Clinical Engineer profession, the health risk of excessive leakage current for hospital patients is not well understood. It is not unusual to see doctors and IT personnel bring in consumer grade computers, printers and other electronic devices to operating or patient care rooms without being aware of the high leakage current from such equipment and its risk to the safety of both staff and patients. No statistics are readily available on how many cardiac arrests or less damaging injuries occur during surgery or during normal patient care that are caused by high leakage current. As many doctors and staff are not aware of the fatal risks from high leakage current, this possible cause may not be considered as the root cause.

Purchasing agents, if not specifically told to purchase a medical grade product, will of course buy the less costly consumer grade computer, printer or TV sets.

Even certified medical grade equipment can cause harmful leakage (touch) current. Reasons may include gradual degradation of components and power supplies due to aging, or the use of defective power strips, power cords, and spillage of fluids on electrical connections. The excessive high leakage current causes the line isolation monitor to set off alarms. The staff may look for the source of the alarm or if surgery is in process simply ignore the alarm hoping it is just a “nuisance alarm”. If the equipment is connected to a GFI (Ground Fault Interruption) outlet, the power will be cut off to the equipment, sometimes putting the patient at risk.  

Installing a separate hospital grade isolation transformer will prevent any of the above incidents from happening.  Some models available on the US market can be wall-mounted and most models can be mounted on medical carts and with a guarantee that the leakage current from consumer grade computers, printers and other non-medical grade or medical grade electronics will not exceed legal limits causing alarms by the line isolation monitor in the operating room, or activate a ground fault interruption device in a wall outlet to cut off power.

In addition to eliminating alarms due to high leakage current, use of these individual isolation transformers allows the purchasing agent to continue saving money from buying consumer grade electronic products with no risk of violating the code for operating rooms and patient care vicinities. The same applies to TV sets, DVD players and other consumer electronics installed in patient care areas and patient rooms.

Summary
Individual hospital grade isolation transformers offer an inexpensive and quick solution to reduce excessive and harmful leakage (touch) current from aging medical devices and consumer grade electronics in the operating room, patient care vicinities, and patient rooms. They allow purchase and use of consumer grade electronics while still be in full compliance with the NFPA 99.   The emphasis in the 2012 edition of a risk based approach to determine levels of patient and staff safety is a good reason to install such isolation transformers, an insurance to provide the ultimate protection.

References
• NFPA 99 2012 Edition Healthcare Facilities Code *
• NEC National Electrical Code
• UL 60601.1 Safety Standard for Electrical Products used in Hospitals and other Patient Care Facilities. **
• Greg Smith NCE, Product Safety Engineer with MET Laboratories Southeast. ***


*    NFPA (a registered trademark of the National Fire Protection Agency) is a sponsor of National Electric Code. The NFPA has no power, nor does it undertake, to police or enforce compliance with the contents of NFPA documents. Nor does the NFPA list, certify, test or inspect products design or installations for compliance with this document.
**   UL safety standards issued by Underwriters Laboratories, Northbrook, IL.
*** Greg Smith can be contacted by email at gsmith@metlabs.com

Advertisement

Share this Story

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading