Local Exhaust Ventilation to Control Air Contaminants
Local Exhaust Ventilation for reducing worker exposure is the best description of ventilation for the purpose of controlling air contaminants that may be released inside the building. The objective is to capture the containment before it reaches the operation and gets into the general air stream. As of 2017, Industrial Production has increased but corresponding efforts to control worker exposure from the emissions from that production have not kept pace. Thus, workers are being exposed to contaminants in their work environment as the demand for American made products increases.
There is a hierarchy of controls to minimize the potential for worker exposure to workplace health hazards where the exposure is through inhalation. This applies to both solids (lead, dust, etc.) and chemicals (vapors, all gases, solvents, acids, pesticides, etc.).
The hierarchy of controls includes:
- Eliminates the Hazard – find a substitute that is less toxic or non-toxic.
- Separate the worker from the contaminant. Isolate the worker from the contaminant or enclose the activity to eliminate exposure.
- Local Exhaust Ventilation – Capture the contaminant before it gets into the worker’s breathing zone.
- General Ventilation – Move the contaminant elsewhere or dilute it to reduce or eliminate worker exposure. Be careful not to just send the contaminant into other workers’ breathing zones.
- Administrative Controls – Minimize the worker’s exposure through a reduction in exposure time. Possibly split work activity with other workers to reduce the time one (1) worker is exposed.
- Respiratory Protection – The most difficult—and generally least effective worker exposure control is respiratory protection—for many reasons:
- The correct respirator must be selected that is specific for the specific contaminant and the concentration of the contaminant.
- Each person’s face is different and the effectiveness of the respirator’s fit can vary considerably.
- Persons must be properly trained in how to wear the respirator.
- The respirator must be inspected, cleaned, properly stored and filter change at proper intervals.
- The worker’s environment may make it difficult to wear. Too Hot, Too Cold, Too Humid, Too Much Motion. The need to communicate with others.
- The wearer must have a well-functioning respiratory system that allows for wearing a respirator for part—or all—of a work shift.
Local Exhaust Ventilation
From an engineering standpoint, local exhaust ventilation is the best approach. Local exhaust is intended to locate the pick-up point of the exhaust close enough to the work activity to draw the contaminant away from the worker’s breathing zone and into a system that can capture and filter the material.
This can apply to such diverse activities as:
- Laboratory hoods
There are specific design parameters to consider: 1) the closeness of the exhaust point, 2) the weight of a particulate, 3) the vapor pressure-(evaporation rate) of the vapor, 4) the temperature of the material (heat rises) 5) the transport velocity—keep it suspended in the ductwork, 6) the filtration system (filters or chemical absorbers), 7) the size and type of fan system, 8) the location of exhaust to the atmosphere (not near air intake), 9) will an air permit be required?
The design must also consider make-up air which often must be heated or air-conditioned to maintain a comfortable—or at least tolerable—temperature. You can’t just add exhaust ventilation without considering the need for wake-up air. If not, the exhaust system will not be able to capture the needed amount of air or the negative pressure will get so great, doors can’t be opened and there are temperature gradient problems throughout the building.