HVAC Journeyman Practice Exam

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A flammable vapor or fume is considered dangerous when it exceeds what percentage of its lower flammability limit (LFL)?

  1. 10%

  2. 25%

  3. 50%

  4. 75%

The correct answer is: 25%

A flammable vapor or fume is considered dangerous when its concentration exceeds 25% of the lower flammability limit (LFL). The LFL is the lowest concentration of a vapor in air that can ignite when exposed to an ignition source. When the concentration reaches or exceeds 25% of the LFL, the mixture becomes highly combustible and poses significant risks for ignition and explosion. Understanding the relationship between flammability limits is crucial for safety in HVAC work and other areas where flammable materials are present. This knowledge helps HVAC technicians ensure proper ventilation and monitor air quality to mitigate risks associated with flammable vapors in the environment.

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