Check Your Local Exhaust Ventilation System
Local exhaust ventilation systems (LEVS) are meant to capture airborne chemicals at the source of generation and remove contaminants from the work area. When a LEVS does its job your workers are healthy and productive. But often LEVS don't do their job. Why?
First, look at the number of components that must be working to ensure a LEVS is functioning properly. A LEVS consists of:
hoods for capturing the contaminant
ducts for transporting the contaminant
air cleaner for removing contaminants from the air stream
fan to create airflow in the system
stack to discharge the air outside the workplace. So, why don't some LEVS do the job? In my experience, a LEVS fails to do the job because the system or one or more of its components were either not designed for the job, or were not installed properly, used properly or maintained properly. To get your LEVS system back on the job you will need to address these areas of possible failure. Know the chemical To design a LEVS you must know all about the chemical you are dealing with and how it is used. For example, know the:
physical state of the chemical (Is it a dust, mist, fume, gas or vapor?),
chemical's toxicity and applicable exposure limits,
physical properties of the chemical (Vapor pressure, boiling point, flash point),
routes of worker exposure -- inhalation, ingestion, skin contact,
how, where and when the chemical is used,
and how the worker does their job.
Hood design -- A well-designed hood is the most important component of an effective LEVS. The hood must be positioned so that it does not pull contaminated air through the worker's breathing zone. It should be easy to use and not interfere with the job that the worker is trying to do. It should be positioned as close to the point of contaminant generation as possible. The further it is from the point where the chemical is released into the air, the more airflow is required to capture the contaminant.
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