HSE Video of Smoke Clearance Testing – Smoke Dispersal in Spray Room

This short HSE video provides a powerful visual demonstration of how airborne contaminants behave inside a typical spray room. Using artificial smoke and accelerated playback, the video illustrates how contaminants can remain suspended within the workspace long after spraying activities have ceased, despite the presence of extraction systems.

The video reinforces the importance of understanding smoke clearance times, ventilation effectiveness and the need for workers to remain protected until airborne contaminants have been fully removed from the enclosure. Although originally produced for the motor vehicle refinishing industry, the principles demonstrated are equally relevant to many enclosed processes where hazardous mists, fumes or dusts may remain airborne after work activities have stopped.

Source Document

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Source: Health and Safety Executive (HSE)
Document Type: HSE Video
Status: Current
Last reviewed by LEVCentral: June 2026

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What This Resource Covers

This resource explains:

Smoke clearance testing principles
Airflow behaviour within spray rooms
Why contaminants may remain airborne after spraying
Clearance times and worker protection
The use of artificial smoke for airflow visualisation
The relationship between smoke testing and LEV performance
Practical implications for LEV testing and occupational hygiene

Why This Guidance Matters

One of the most common misconceptions surrounding ventilation systems is that contaminants are removed immediately once extraction is operating.

The HSE video demonstrates that this is often not the case. Smoke introduced into the spray room disperses rapidly throughout the enclosure and then appears to linger, with relatively slow movement occurring throughout much of the workspace. Directional airflow is only clearly visible close to extraction points and air inlets.

The behaviour shown in the video mirrors the way paint mist and other airborne contaminants behave during real work activities. This is particularly important where hazardous substances such as isocyanate-containing paint products are used. HSE notes that contaminant levels within spray rooms have been measured at many times the workplace exposure limit and may take significant time to clear following spraying operations.

Smoke Clearance Testing and LEV

Smoke clearance testing is commonly used to establish how long an enclosure takes to remove airborne contaminants once the process has stopped.

The technique involves:

Filling the enclosure with artificial smoke
Operating the extraction system
Measuring the time required to completely clear the smoke
Identifying stagnant areas or dead spots
Checking for leakage from the enclosure or ductwork

The resulting clearance time can then be displayed for operators so they know when it is safe to remove respiratory protective equipment or enter the enclosure without exposure risks.

Key LEVCentral Takeaways

Airborne contaminants often remain suspended far longer than operators expect.
Smoke provides an excellent visual representation of contaminant behaviour.
Extraction systems may only create obvious directional airflow close to inlets and exhaust points.
Clearance times should be established and communicated to workers.
Smoke testing can identify dead spots and ineffective airflow patterns.
Clearance testing forms an important part of evaluating enclosure performance.
Workers should not remove respiratory protection until the enclosure has fully cleared.

Further Resources

Related LEVCentral Resources:

HSG258 – Controlling Airborne Contaminants at Work
HSG261 – Health and Safety in Motor Vehicle Repair
Understanding Captor Hood Performance
Introduction to Smoke Testing LEV Systems
Time to Clear the Air – A Worker’s Guide to LEV
LVHV and On-Tool Extraction Resources

Recommended Learning

Thought Leadership

The value of this HSE video lies in its simplicity. Air movement is normally invisible, making it difficult for workers and managers to appreciate how contaminants behave once released into the workplace atmosphere.

By visualising airflow using smoke, the video demonstrates an important occupational hygiene principle: contaminants do not disappear simply because a process has stopped. Understanding how long hazardous substances remain airborne is essential when determining clearance times, selecting respiratory protection and evaluating the effectiveness of ventilation systems.

For LEV professionals, smoke remains one of the most powerful diagnostic tools available because it allows airflow behaviour to be seen rather than assumed.