Which of the following is NOT listed as an indication of a physical action?

• A. Activated Pressure-Relief Devices
• B. Pinging or Popping of Heat-Exposed Vessels
• C. Wavy Vapors Over the Surface of a Liquid Puddle
• D. Leaking from a Valve or Gasket

Answer: (C)

The concept being tested is recognizing signs that indicate the container or system is undergoing a physical action—things the vessel does as a response to pressure, heat, or mechanical stress.

Activated pressure-relief devices are clear physical actions: the system is venting to relieve pressure, a direct, observable mechanical response.

Pinging or popping of heat-exposed vessels is another physical action sign: the vessel is mechanically reacting to pressure buildup, often producing sounds as it strains or vents.

Leaking from a valve or gasket is also a physical action: a release path opening up and letting contents escape is a tangible action of the equipment.

Wavy vapors over the surface of a liquid puddle, however, are not an action performed by the container or its components. They reflect evaporation or vapor formation due to heat, not a device venting, popping, or leaking. So this sign isn’t considered a physical-action indication, even though it signals the presence of vapors and hazard.