Chapter 17. Ventilation

I. It is good practice essential to use appropriate types of ventilation to prevent or control harmful worker exposure to air contaminants and hazardous vapors. There are five types of operations that require specific ventilation: abrasive blasting; grinding, polishing, and buffing; spray finishing operations; open surface tanks; welding operations.

II. Indication that ventilation is needed include eye, nose, and throat irritation; dust and smoke clouds arising from operation; dust settling over equipment floors and other surfaces; a visible haze in the air; or a strong odor of solvents or gas.

III. The first choice for controlling the health hazards of air contaminants is by engineering controls. A properly designed system has the added advantage of reducing or eliminating fire. There are two types of exhaust ventilation that can be used to control air contaminant hazards.

A. Local exhaust ventilation. This type of mechanical exhaust removes hazardous materials as close as practical to the point of origin. This is usually accomplished by the use of hoods and ducts. Local exhaust ventilation removes air contaminants without pulling them through the breathing zone of workers. Local exhaust is the preferred type of mechanical ventilation to be used wherever large volumes of air contaminants are generated or in operations where a particularly hazardous substance is used.

B. General dilution ventilation. This system uses fans to pull a sufficient volume of air through the work area to dilute air contaminants to a safe level. Dilution ventilation requires a greater volume of air movement for efficient operation than does a local exhaust. General dilution ventilation is an effective control for areas with low concentrations of low or moderately hazardous substances.

IV. Design of effective and efficient ventilation systems often requires skilled assistants. An engineer should be consulted when workplace ventilation systems are being considered.

V. All ventilation systems need to be regularly examined and maintained to ensure continued efficient functioning. For example, ducts need to be cleaned; Z-belts or chain drives on sand need to be checked for slippage, breaks, or excessive wear; and the whole system needs to be checked for loose, damaged, or broken duct work.

VI. For consideration of the use of fume hoods in laboratories see the Laboratory Safety Manual. Laboratory fume hoods are used to confine and exhaust odiferous , corrosive and toxic vapors generated in a laboratory. Do not use laboratory fume hoods for storage of chemicals.