CABT Healthcare and Electrical Safety 3 — Questions and Answers
Question 1: Which NFPA 99 category designation applies to spaces where failure of equipment is likely to cause major injury or death to patients or caregivers?
- Category 1 (Correct answer)
- Category 2
- Category 3
- Category 4
Correct answer: Category 1
NFPA 99 Category 1 (formerly 'critical care') covers areas where equipment failure could result in major injury or death.
Question 2: Which physiological effect occurs when 60 Hz AC current in the range of 10–20 mA passes through the thorax?
- Tingling sensation only
- 'Let-go' threshold exceeded, causing inability to release the conductor (Correct answer)
- Ventricular fibrillation
- Respiratory arrest without cardiac involvement
Correct answer: 'Let-go' threshold exceeded, causing inability to release the conductor
At 10–20 mA, sustained muscle tetany prevents voluntary release of the energized conductor, defining the 'let-go' threshold.
Question 3: A line isolation monitor (LIM) alarms at 5 mA. Which action is most appropriate?
- Immediately shut off all power in the OR
- Unplug equipment one at a time to identify the faulted device (Correct answer)
- Ignore the alarm if surgery is in progress
- Replace the LIM unit
Correct answer: Unplug equipment one at a time to identify the faulted device
Sequentially unplugging devices while watching the LIM reading identifies the faulted equipment without interrupting essential power.
Question 4: What does the term 'double insulation' (Class II equipment) mean?
- Two separate ground wires inside the power cord
- Two independent layers of insulation so no grounding conductor is needed (Correct answer)
- Two-phase power supply for redundancy
- Dual leakage current testing at twice normal voltage
Correct answer: Two independent layers of insulation so no grounding conductor is needed
Class II (double-insulated) devices have two independent insulation barriers, eliminating the need for a protective earth connection.
Question 5: For cardiac catheterization laboratory equipment, NFPA 99 specifies a maximum patient lead leakage current of:
- 500 µA
- 100 µA
- 50 µA
- 10 µA (Correct answer)
Correct answer: 10 µA
In critical care (Category 1) areas with intracardiac leads, the patient lead leakage limit is 10 µA to prevent microshock-induced fibrillation.
Question 6: Which standard specifically governs the safety requirements for medical electrical equipment at the international level?
- IEC 60601-1 (Correct answer)
- OSHA 1910.303
- NFPA 70
- IEEE 802.11
Correct answer: IEC 60601-1
IEC 60601-1 is the international standard defining safety and essential performance requirements for medical electrical equipment.
Question 7: Stray capacitance in medical equipment can cause:
- Increased device gain
- Unwanted leakage current flow through non-conductive paths (Correct answer)
- Reduced electromagnetic emissions
- Higher ground-fault impedance
Correct answer: Unwanted leakage current flow through non-conductive paths
Stray capacitance between energized conductors and the chassis creates a capacitive path for leakage current even through nominally non-conductive materials.
CABT Healthcare and Electrical Safety 3
Which NFPA 99 category designation applies to spaces where failure of equipment is likely to cause major injury or death to patients or caregivers?