HFC-152a MVAC systems are acceptable if designed to avoid passenger cabin concentrations above what percentage for more than 15 seconds?

For HFC-152a MVAC (Motor Vehicle Air Conditioning) systems, it is critical to ensure that the concentration of the refrigerant in the passenger cabin remains below a specific threshold to protect occupants’ health. The acceptable concentration level is established to prevent potential health risks, as higher concentrations can lead to a variety of harmful effects.

The correct answer reflects the guideline that concentrations in the passenger cabin should not exceed 3.7% for more than 15 seconds. This limit is based on safety assessments that analyze both the flammability of the refrigerant and its effects on human health when inhaled. Keeping concentrations below this level ensures that the refrigerant remains safe for passenger exposure during the operation of the MVAC system.

Understanding this limit is essential for technicians, as it impacts the design and operation of air conditioning systems in vehicles using HFC-152a, ensuring they adhere to safety regulations while maintaining functionality. A lesser percentage would not represent the maximum allowed concentration and could lead to unnecessary restrictions or inappropriate design choices for those systems.