Flammability Characteristics and Metrics Flashcards
6 cards from real A2L practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Flammability Characteristics and Metrics flashcards as text
What does the Lower Flammability Limit (LFL) of a refrigerant represent?
Answer: The minimum concentration of refrigerant in air required for ignition and flame propagation.
The LFL is a critical safety metric defining the lowest concentration of a flammable gas or vapor in the air that can ignite and sustain a flame. Below this concentration, there isn't enough fuel for combustion to occur, making the mixture 'too lean' to burn.
Which combination of characteristics defines an A2L refrigerant according to ASHRAE 34 and ISO 817 standards?
Answer: Lower flammability limit (LFL) > 3.5% by volume, burning velocity < 10 cm/s.
A2L refrigerants are classified as 'mildly flammable.' This means they have an LFL greater than 3.5% by volume, indicating a higher concentration is needed for ignition, and a low burning velocity of less than 10 cm/s, meaning a slower flame spread. These specific thresholds differentiate them from highly flammable (A3) or non-flammable (A1) refrigerants.
A technician is working with an A2L refrigerant and is concerned about potential ignition sources like electrical sparks. Which flammability characteristic indicates how easily the refrigerant-air mixture can be ignited by such a source?
Answer: Minimum Ignition Energy (MIE)
Minimum Ignition Energy (MIE) is the smallest amount of energy required to ignite a flammable mixture. A lower MIE indicates that a mixture can be more easily ignited by small sparks or electrostatic discharge. While AIT is also about ignition, MIE specifically refers to the energy required from an external source like a spark.
If a refrigerant has a Lower Flammability Limit (LFL) of 5% by volume and an Upper Flammability Limit (UFL) of 15% by volume, what is its flammability range?
Answer: 5% to 15% by volume
The flammability range is the entire span of concentrations in air, between the LFL and UFL, where the refrigerant can ignite and sustain a flame. Therefore, from 5% up to 15% by volume, the mixture is flammable.
What is a defining characteristic of A2L refrigerants regarding their burning velocity?
Answer: Their burning velocity is typically less than 10 cm/s.
The 'L' in A2L specifically stands for 'low burning velocity.' According to standards like ASHRAE 34, an A2L refrigerant must have a maximum burning velocity of less than 10 cm/s, which is significantly slower than highly flammable refrigerants (A3).
Which of the following factors can significantly influence the flammability limits (LFL and UFL) of a refrigerant-air mixture?
Answer: The presence of non-flammable inert gases (e.g., nitrogen used for purging) and ambient temperature.
Both ambient temperature and pressure directly affect the density and partial pressures of the refrigerant and oxygen in the air, thereby influencing the flammability limits. Additionally, the presence of inert gases dilutes the oxygen concentration, narrowing the flammability range or rendering the mixture non-flammable. Therefore, option 4 is the most comprehensive correct answer.