This is video footage shot at the Health and Safety Laboratory showing an operative with an HVLP spray gun with an empty paint canister (ie ejecting compressed air). Another person is positioned alongside the sprayer with a professional smoke machine. Behind them is a black backcloth marked with vertical white lines every half metre from 0 to 5.5m.
The sprayer pulls the trigger of the spray gun at the same time as the smoke machine is operated – injecting smoke into the path of the compressed air released from the gun. The smoke is propelled by the compressed air across the room, well past the 5.5m mark (a typical width for a spray booth). In fact, measurements taken at the tip of the gun show that the compressed air leaves with a velocity of over 100 metres per second. Typical vertical flow rates for extraction in spray booth are about 0.3 m/s ie the compressed air velocity is over 300 times greater! This explains why any extraction system is completely overwhelmed by the spraying operation and why sprayers must always wear air-fed breathing apparatus during spraying and during the clearance time.