The V-Ray Volume Fog node creates a simple fog effect that can be confined to a container. 

V-Ray Volume Fog can use either of two algorithms to calculate volumetric lighting. The first algorithm is a simple exponential sampling scheme, which is used when there are no texture maps specified. In this mode, the V-Ray Volume Fog takes a number of random points inside the volume and calculates the volumetric lighting at those points. The second algorithm is a raymarching scheme, which is used when any of the volume properties are mapped with a texture. In that case, V-Ray Volume Fog traverses the fog volume in small steps, calculates the volume properties at each step, and computes the volume lighting accordingly.

The Volume Fog is more suited for creating simple fog effects inside containers. If you would like to create realistic atmospheric fog, dust, etc., you need to use the Environment Fog node.

In the example, the Emission is set to a reddish color, which tints the ambient occlusion and any items outside of direct light in a red tint. The Color parameter is set to a blue color, and therefore, lights illuminating the scene have a blue tint. You can see the scene without Volume Fog looks quite different.

UI Path: ||V-Ray Node Editor|| > World > Add > Effects > V-Ray Volume Fog

Emission (input node) – Allows a color node to control the Emission color.

Color (input node) – Allows a node to control the Color of the fog.

You can find the parameters of this node either in the Node menu in the V-Ray Node Editor or in the World Properties tab.

Closed Volume – 

Emission – Controls the fog emission (self-illumination). This parameter is used to substitute the ambient illumination inside the fog, instead of using GI. A node texture can also be connected here.

Color – Defines the color of the fog when it is illuminated by light sources. A node texture can also be connected here.

Color multiplier – A multiplier for the Color parameter.

IOR – Index of refraction for the volume. If simulating a fog inside an enclosed volume, light rays entering or leaving the volume are refracted based on this parameter.

Bias – This parameter changes the way the Color is applied. By adjusting the Bias, you can make thin parts of the volume appear more transparent than normal or less transparent than normal.