NFPA 99 Impedance Testing

Reasons for Testing

• Static electricity can ignite with gases, such as anesthesia, or create flash fires where medical oxygen is used. Impedance testing is done to verify the floors are antistatic. Given the risk electrical shock poses to patients, medical buildings must also meet high impedance testing standards for electrical equipment. A high level of impedance is necessary because impedance is the measure of the resistance to the flow of electricity from electrical equipment to people, thus a measure of how well the system or floor prevents electrical shock.

System Ground Testing

• NFPA 99 Chapter 4 defines the necessary testing of the grounding system. The grounding system prevents electrical shock of either health care workers or patients from electrical equipment. NFPA standards require testing of the voltage and impedance of the grounding system. According to "Complications in Anesthesiology" by Emilio Lobato, Nikolaus Gravenstein, and Robert Kirby, "the impedance between the current-carrying wire and the ground must exceed 200,000 ohms."

Antistatic Floor Testing

• According to "Power Quality" by C. Sankaran, "the requirements for health care facilities stipulate a maximum resistance of 10 to the 6th power ohms of floor resistance by using two test electrodes, each weighing 5 lbs. with a circular contact area 2.5 inches in diameter. ... The resistance between the points is measured with an ohm meter, which has an open circuit voltage of 500 VDC and nominal internal impedance of not less than 100,000 ohms." By proving that the floor cannot carry such a high level of current, the floor is thus proven safe. It cannot carry an accidental static shock to a weakened patient or a minor electrical flow from a wire to nearby medical equipment.