Common processes and sources - LEV
When developing exposure control measures, ‘process’ means the way airborne contaminants are generated, for example in woodworking, processes would be cutting, shaping and sanding. The source is where the contaminant is generated by a process. Understanding the process means understanding the creation of ‘sources’. This can suggest ways to modify the process to reduce the number or size of sources, and contaminant clouds. The effective application of LEV requires a good understanding of the process and the sources.
Further information on process and source descriptions is available to accompany the video presentations.
To expand the playlist and choose a video select the YouTube playlist icon . The videos in the playlist are:
What is LEV?
A description of what LEV is, its key components and how the system works to protect health.
Unguarded circular saw
Air movement is made visible with smoke. The rotating circular saw blade acts as a crude fan. It draws air in along the axis of blade rotation and throws it out as a jet in line with the blade. The airflow is directed and shaped by the saw table. A narrow and a fan-shaped air jet are created.
Circular saw with LEV hood (guard)
Air movement is made visible with smoke. The saw-blade LEV hood (guard) copes with and contains the vertical air-jet . The wide, fan shaped, air jet is partially extracted but part of it escapes and flows towards where the saw operator would stand. The LEV hood isn't big enough and the extracted airflow is too low i.e. the hood isn't emptied as fast as it is filled.
Air movement is made visible with smoke. The narrow compressed air-jet leaves the spray gun "air-cap" at over 100 metres per second. It flows rapidly away from the spray gun growing in size by induction of spray room air. The total ‘throw’ may be over 12 metres. The air jet is energetic and difficult-to-control.
Cleaning badly contaminated clothes using compressed air
The compressed air jet travels at high velocity and moves a large volume of air. When used to clean clothing it creates a large dust cloud surrounding the worker.
Cleaning badly contaminated clothing using hands
Dust contaminates work clothing by direct contact with powder and settled dust. Patting the clothing releases the retained dust and produces an airborne cloud surrounding the worker. Some fabrics, such as cotton, retain and release far more dust than more modern fabrics.
Compressed air used to clean a surface
The compressed air jet travels at high velocity and moves a large volume of air. When used to clean surfaces or components it makes solid debris airborne as dust, or liquids airborne as mist. Because it is so energetic the airborne contaminant cloud created is large, fast moving and very difficult to control.
Shock - hammer strike to the underside of a dusty surface
Settled dust or spilt powder can be released from a contaminated surface and propelled into the air by impact. The amount of airborne dust released will depend on the degree of surface contamination, the nature of the dust, and the energy (frequency and amplitude) of the shock applied to the surface.
The workers' clothing becomes directly contaminated each time he picks up a powder covered sack. Each time he drops a sack onto the pile, dust is made airborne by the direct impact and by air displacement between the falling sack and the one below.
Wood stacking - bellows effect
The top sheet of wood suddenly falling onto the one below causes a ‘bellows effect’ causing rapid displacement of dust-laden air.
The fine dust created by hand sanding of and made airborne is shown up using a dust-lamp. In normal lighting the fine dust cloud is not visible.
Effective LEV system
An example of an effective system employed in a woodworking classroom.
A series of four videos showing effective capture of welding fumes using:
- a conventional capture hood
- a high vacuum nozzle
- on-torch extraction demonstrated by showing the on-torch extraction switched on and off during welding
- a demonstration showing how much welding fume can be captured using on-torch extraction in twenty seconds of welding
Wood dust capture
A demonstration of effectiveness by showing how much wood dust can be captured using on-tool extraction in twenty seconds when sanding a piece of wood