CABT Healthcare and Electrical Safety 5 — Questions and Answers
Question 1: An electrically susceptible patient (ESP) is one who has a direct conductive pathway to the heart. The ventricular fibrillation threshold for such a patient is approximately:
- 500 µA
- 100 µA
- 10–20 µA (Correct answer)
- 1 mA
Correct answer: 10–20 µA
Current as low as 10–20 µA applied directly to the myocardium can trigger ventricular fibrillation in electrically susceptible patients.
Question 2: The 'source leakage current' measured during medical device safety testing represents current flowing:
- From the power source through the chassis to ground without any external patient load (Correct answer)
- From the patient leads to the neutral wire
- Between two pieces of equipment connected in series
- Through the signal output connector only
Correct answer: From the power source through the chassis to ground without any external patient load
Source leakage current (also called chassis or enclosure leakage) flows from the power-line conductors through insulation to the chassis and then to ground.
Question 3: Which organization publishes the Health Care Facilities Code that governs electrical safety requirements in US hospitals?
- OSHA
- NFPA (Correct answer)
- FDA
- The Joint Commission
Correct answer: NFPA
NFPA 99, Health Care Facilities Code, published by the National Fire Protection Association, sets US electrical safety standards for healthcare environments.
Question 4: During preventive maintenance, a technician measures 0.15 Ω between two metal IV poles in the same patient room. Per NFPA 99, this finding indicates:
- A safe result within the 0.5 Ω limit
- A marginal result; both poles should be rebonded to the ground bus
- An unsafe condition exceeding the 0.1 Ω limit (Correct answer)
- No action required since IV poles are not patient-connected
Correct answer: An unsafe condition exceeding the 0.1 Ω limit
NFPA 99 requires that resistance between any two exposed conductive surfaces in a patient care vicinity not exceed 0.1 Ω; 0.15 Ω exceeds this limit.
Question 5: Which type of power outlet is required by NFPA 99 to be supplied by the emergency essential electrical system in an operating room?
- Standard 120 V duplex only
- Red-colored receptacles connected to the critical branch (Correct answer)
- Blue GFCI receptacles
- Any NEMA 5-15R receptacle with a twist-lock adapter
Correct answer: Red-colored receptacles connected to the critical branch
Red receptacles in ORs are connected to the critical branch of the essential electrical system, ensuring power during a utility failure.
Question 6: A biomedical technician notices that a defibrillator's internal batteries have a charge but the device fails the leakage current test when powered by AC. The most likely cause is:
- A failed battery charger circuit
- Degraded or damaged AC power supply filter capacitors allowing excess leakage (Correct answer)
- An incorrectly calibrated leakage meter
- Electromagnetic interference from nearby equipment
Correct answer: Degraded or damaged AC power supply filter capacitors allowing excess leakage
Failed or aged EMI filter capacitors in the AC power supply provide a low-impedance path to ground, significantly increasing measured chassis leakage current.
Question 7: The term 'patient environment' or 'patient care vicinity' as defined by NFPA 99 refers to a space extending:
- 6 feet horizontally and 7.5 feet vertically from the patient bed edge (Correct answer)
- 3 feet horizontally and 5 feet vertically from the patient's head
- 10 feet in all directions from the patient
- The entire patient room floor area
Correct answer: 6 feet horizontally and 7.5 feet vertically from the patient bed edge
NFPA 99 defines the patient care vicinity as a zone 6 feet horizontally from the bed edge and up to 7.5 feet above the floor.
CABT Healthcare and Electrical Safety 5
An electrically susceptible patient (ESP) is one who has a direct conductive pathway to the heart.
The ventricular fibrillation threshold for such a patient is approximately: