...

Smoke Volume
Required string field to render expected density. Should always have a specified float field. Field The field is used in the Density Float parameter of PxrVolume shader

...

Source Volume
Field used to generate scatter data from.

Mask Volume
Field used to generate a multiplier to control the area of effect for the scatter data generated from the Scatter Source Volume.

Scatter Volume
Required string field to write scatter results to.

...

Fire
Intensity Volume

Field used to generate base color and intensity values for the Diffuse Color Volume and Emit Color Volume.

Flame Volume
Field used to define the area of application of color and intensity data from the Intensity Volume using the Fire Mask options in the Fire tab. Also is used to replace the density float value when Smoke is disabled

...

Diffuse Color Volume
Required string field to have pyro render with user-designed color instead of the non-default color of (1,1,1). Field is used in Diffuse Color parameter of PxrVolume shader

...

Emit Color Volume
Required string field to have pyro render with user-designed color instead of the non-default color of (0,0,0). Field is used in Emission Color parameter of PxrVolume shader.

...

Velocity Volume
Required string field to use velocities generated from simulation for motion instead of the default value (0,0,0) or uniform direction specificed specified by the user in the Render tab. Empty An empty string field will reveal uniform direction velocity parameters in the Render tab. Field
The field is used in the Velocity parameter of PxrVolume shader.