Back-Draft exhaust hoods and systems can be an essential component of a Local Exhaust and Ventilation system.
Key Design Criteria:
Capture velocity: When designed with capture velocity in mind, Back-Draft hoods are an excellent 'No-Fuss' way of removing respirable hazards and improving air quality in your facility. All aerosols have a speed at which they can be drawn into a hood. You must be able to capture it if you are going to control it.
Face Velocity: Understanding the appropriate face velocity is not only essential for the proper capture of airborne pollutants, but it will also determine the noise generated at the hood. It is common to see poorly designed LEV systems with unacceptable noise levels.
Transport Velocity: Evaluating your hood's transport velocity will help you understand whether you will have the contaminant fall out of the airstream and stay in your hood. This could lead to a falling hazard or, perhaps worse, a fire hazard.
If you take the time and follow these and other relevant design criteria & recommendations such as ASHRAE, SMACNA, ACGIH, you will be well on your way to a successful ventilation solution.
Answer: An extraction arm is a Capture or receiving device designed to capture aerosols at the emission point before the contaminants have a chance to reach the workers' breathing space.
Typically, it is the 1st and most crucial part of an LEV or Local Exhaust & Ventilation system. NB: NB: Local exhaust ventilation can also be referred to as Process ventilation or Industrial Ventilation, or Local Control ventilation.
Available in several different designs:
- Internally Supported
- Externally Supported
- Mild or Stainless Steel Construction
- Lengths: Up to 45'
- 2.5" to 8" Diameter's Available
2. What applications are best served by extraction arms?
Answer: Here is a list: (List all of the Process linked to the catalogue solution called "Extraction arms")
3. Can "extraction arms" make toxic work places spaces safe from Airborne contaminants?
ANSWER: Yes, but only when systems the systems are designed, installed and used precisely. Unlike Dilution ventilation, Extraction arms can return significant energy savings and improvements in health and safety. However, the precision at which they must be designed, installed and used can be complex. Lev-co recommends that these three procedures OSHA's HOC(hierarchy of controls) and MOC (management of change) and PSR (Pre-start Safety review), when appropriate, should be used when selecting extraction arms as a capture method.
Here are links to examples of these 2 procedures:
OSHA Hierarchy of controls (https://www.osha.gov/sites/default/files/2019-03/health_hazards_workbook.pdf
MOC Management of change sample document (https://www.safer.ca/docs/safer_combustible_dust_management_of_change_handout.pdf)
PSR Pre-start Health and Safety review (https://www.osha.gov/sites/default/files/publications/osha3132.pdf)
4. What industries and environments are extraction arms used in?
ANSWER: Here are the various industries using extraction arms: (Show links to relevant industries)
5. What are the different types of extraction arms available?
ANSWER: See our offering of fume extractors here: (Show list from catalogue section)
5.5 What are the selection criteria that must be considered when selecting an extraction arm?
ANSWER: See Below:
- Capacity (How much flow will the extraction arm handle?)
- Capture velocity (can the extraction accommodate the required capture velocity to capture the aerosol?)
- Easy to use (How many articulations/joints does the extraction arm have?)
- Stay in place? (Does the extraction stay in place, how often do the joints need to be tightened?
- Extension hoods (Do you need a large diameter extension hood, eg 36" diameter?) (Optional)
- Can the extraction arm withstand the Pressure/abraision/corrosion/etc?
What are the pros and cons of extraction arms versus other types of capture methods?
Remove airborne toxins at source before they enter any worker“s breathing zone
Low energy costs (Heat loss, electrical energy)
Allow the use of smaller filtration equipment
Well suited for "on-demand" controls allowing for greater flow at the source, yet lower overall flow
Some extraction arms allow the supporting of items like wire feeders, Compressed air cord reels and electrical cord reels for increased productivity
Better visibility through the addition of hood-mounted lighting solutions
Optimized hoods, large-diameter receiving hoods and hose extensions are effective solutions where capture or hood placement is difficult
hood can be rotated 90 degrees (perpendicular to the floor), eliminating shadowing
when used correctly, the operator can visually see the contaminant being safely drawn away from the process Con's:
Operator needs to be comfortable with the use of the arm to ensure adequate capture
Arms not always available in larger diameters for required capture velocity
Production time lost to place the extraction arm in place
Cannot always reach the point of emission
Worker buy-in is not always achieved due to lack of fume capture
Fugitive emission released into the workspace
Some extraction are not built to withstand the working environment
poor design can lead to excess capture velocity resulting in extra capture velocity (Shielding gases loss) and air noise.
Various Options in Filtering Systems Available:
- Washable Filters
- Cleanable Filters
- Self-Cleaning Systems
- Throw Away Filters
For more info, please see the products and associated documentation listed below.