BLOCK 4: CHEMICAL CONTROLS - Unit 5: Dilution Ventilation & Unit 6: Local Exhaust Ventilation (complete) Flashcards
Introduces uncontaminated air for the purpose of reducing airborne concentrations and controlling potential airborne health hazards, fire and explosive conditions, odors, and nuisance contaminants; the contaminant is allowed to disperse to some extent and is then gradually removed.
DILUTION VENTILATION
Air movement within a workplace caused by wind, temperature differences,
or other factors where no fan or other mechanical air mover is used.
NATURAL VENTILATION
Accomplished accordingly with the use of a fan and usually distinguished by providing either negative or positive pressure.
MECHANICAL VENTILATION
TRUE OR FALSE:
Local exhaust ventilation (LEV) systems are generally superior to dilution ventilation systems
because LEV systems remove the contaminant from the work environment, reduce overall airflow rates, and are more economical.
TRUE
There are, however, many industrial operations where LEV is impractical, not cost effective, or impossible to install. Such operations often use dilution ventilation.
TRUE OR FALSE:
DILUTION VENTILATION will remove all of the contaminants from the work area by dilution, providing no exposure if working properly.
FALSE
Dilution does not completely remove the contaminants from the work area, so
there will usually be some level of exposure. Note: Dilution ventilation should not
be used to control chemicals with an OEL < 100 ppm.
What are some of the reasons why dilution ventilation may be chosen over local exhaust ventilation (LEV)?
- Usually lower equipment and installation costs
- Requires less maintenance
- Effective control for small amounts of low toxicity chemicals (OEL > 100 ppm)
- Systems typically not co-located with the source of contamination, which prevents
interference with the worker’s ability to perform a specific operation
What are some of the disadvantages of using a dilution ventilation system?
- Does not completely remove contaminants
- Cannot be used for high toxicity chemicals (OEL < 100 ppm)
- Ineffective for large amounts of dusts, fumes, gases or vapors
- Ineffective for handling surges of gas or vapor emission or irregular emissions
_______________ is how many times the air volume of the room is replaced in one hour of time.
AIR CHANGES PER HOUR (AC/hr or ACH)
REFERENCE
A combination of supply (make-up air) and exhaust is preferred for proper distribution and dilution. Supply is often used alone with satisfactory results, but exhaust alone cannot usually provide proper dilution.
REFERENCE
FORMULAS:
Does dilution ventilation remove contaminants from the worker’s breathing zone?
NO
It only maintains concentrations at a lower level.
A ventilation system designed to capture and remove emissions prior to their escape into the workplace environment.
LOCAL EXHAUST VENTILATION SYSTEM (LEV)
LEV is a _______________ means of controlling employee exposure to gases, vapors,
and particles in traditional workplaces.
PRIMARY
The exhaust systems are termed “local” in the sense that the hood providing suction is located _______________ to the source of contamination.
CLOSE
An _______________ hood completely or partially encloses the
contaminant.
ENCLOSING HOOD
Examples include large paint booths, glove boxes, bead blasting units, and laboratory hoods
Hoods located adjacent to an emission source but
do not enclose the emission source.
EXTERIOR HOOD
Examples of exterior hoods are slots along the edge of the
tank or a rectangular opening on a welding table.
Other places to look to for design criteria would be __________.
–>ACGIH’s Industrial Ventilation, a Manual of Recommended Practice
for Design, also known as the Industrial Ventilation Manual.
–>Another useful reference to find key parameters of a ventilation system is in DOEHRS, or your shop may have its own ventilation pre-survey form.
REFERENCE CARD
