Cause of Device-Related Incident
Device factors; External factors

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering; Obstetrics and Gynecology; OR / Surgery

Device Factors
Improper modification

Document Type
User Experience Network (UEN) reports

External Factors
Power supply (including piped medical gases)

Mechanism of Injury or Death
Electrical shock / electrocution; Fire

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

Isolated Power Systems [15-817]; Plugs, Explosion Proof [15-848]

OR Renovations and the Use of Isolated Power and Explosion-Proof Plugs

User Experience Network™ [Health Devices Sep 1992;21(9):334-5]


We are in the process of renovating our ORs. Our existing ORs have isolated power and explosion-proof plugs. Is it necessary to continue using these systems, or can we use normal ground-referenced power and parallel-blade plugs and receptacles?

Discussion of codes and standards

The National Fire Protection Association (NFPA) mandates the use of isolated power and explosion-proof outlets and plugs only in anesthetizing locations where flammable anesthetics are not banned (NFPA 99, Section 12-, Hospital Requirements—Isolated Power Systems, 1990 edition). NFPA has maintained its position on isolated power since at least 1984, and this requirement can also be found in the 1990 editions of (1) NFPA 70, the National Electric Code, Article 517—Health Care Facilities, and (2) NFPA 99, Section 3-, Electrical Systems—Isolated Power.

In addition, the NFPA documents make it clear that isolated power is one of the acceptable means of protection in areas designated by the hospital as wet locations where the use of ground-fault circuit interrupters (GFCIs) is not clinically acceptable. NFPA 99, Section 2-2, Definitions of Terms Used in the Standard, defines a wet location as "a patient care area that is normally subject to wet conditions while patients are present. This includes standing fluids on the floor or drenching of the work area, either of which condition is intimate to the patient or staff. Routine housekeeping procedures and incidental spillage of liquids do not define a wet location."

Although NFPA codes and standards are only voluntary guidelines, most states and local municipalities adopt NFPA 70 as their electrical code; hospitals must conform to this code at the state and local level or apply for variances if the proposed systems are different. The codes and standards do not prohibit mixing isolated power with normal power as long as isolated power is not required in the area. If these power sources are mixed, the distribution system from which they are supplied must be clearly marked on the outlets.


Most ORs in the United States have banned the use of flammable anesthetics, and we are not aware that hospitals are (routinely) designating ORs as wet locations; therefore, the need for isolated power rarely exists today. However, if the use of flammable anesthetics has not been banned or if state or local regulations require its use, isolated power would still be needed.

Initially, isolated power was required to minimize the risk of fire from electrical ignition of flammable anesthetics because it limited the chance of spark generation from a device to a grounded piece of metal. However, this risk has virtually been eliminated by the use of nonflammable anesthetics. Much later, isolated power was touted as a method of reducing the risk of shock. However, the construction of contemporary electrical devices limits the risk of electric shock, and devices with integral isolated outputs are used for invasive procedures to protect patients from microshock.

Some reasons why hospitals may want to refrain from specifying isolated power are that these systems are expensive to install, they must be periodically inspected and maintained (see NFPA 99, Section 3-4.3, and the Health Devices Inspection and Preventive Maintenance System for further information), and they must be provided with a functioning line isolation monitor. The monitor must have both visual and audible alarms and must be visible to an attending staff member (e.g., in the OR, at an ICU central station).

In a previous User Experience Network article (Health Devices 17[5]:170, May 1988), we discussed methods of converting existing isolated power systems to grounded power. Our recommendation continues to be to avoid isolated power and its higher costs (for installation and maintenance), except where it is required by state or local electrical codes or in designated wet locations where the use of GFCIs is inappropriate.


  • Isolated Power Systems [15-817]
  • Plugs, Explosion Proof [15-848]

Cause of Device-Related Incident

Device factor: Improper modification

External factor: Power supply

Mechanism of Injury or Death

Fire; Electrical shock/electrocution

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