A ULV cold fogger differs from ordinary sprayers because droplet size can be adjusted, which is what makes it suitable for precision work such as disinfecting buildings, hospitals and food plants.

Droplets that are too fine drift away in the air. Droplets that are too large fall immediately and become water. Both give results below what is required, and in a hospital the second also creates a wet floor hazard.

This article tells the true story of a mid-sized private hospital in Bangkok that found its ULV adjuster turning without any effect at all, and explains what causes this and how it is repaired.