Electrostatic Precipitator (ESP) Ozone Safety
 What is Ozone?
Ozone is a naturally occurring gas created by the force of corona discharge during a lightning storm, by UV light from the Sun and by the operation of electrostatic precipitation.
Ozone (O3) is an allotrope of Oxygen (O2). It is 1.5 times as dense as oxygen and 12.5 times more soluble in water and leaves no residuals or byproducts except oxygen and a minimal amount of carbon dioxide and water. It can be manufactured from dry air or from oxygen by passing these gases through an electric field of high potential sufficient to generate a "corona" discharge between electrodes (of an ESP).
Ozone is highly unstable and must be generated on-site. The measure of an oxidizer and its ability to oxidize organic and inorganic material is its oxidation potential (measured in volts of electrical energy). Ozone's oxidation potential (-2.07V) is greater than that of hypochlorite acid (-1.49V) or chlorine (-1.36V), the latter agents being widely used in water treatment practice.
EPA Safety Guidelines
Ozone is a toxic gas and, like chlorine, can cause severe illness and death if inhaled in sufficient quantity. One safety advantage is the physical characteristic of ozone that allows it to be detected (smelled) at concentrations much lower than harmful levels.
Recommended Exposure Limit to Ozone:
A study of the health effects of ozone exposure was conducted by the United States Air Force. Another summary of the health effects of ozone was compiled by the American Society for Testing and Materials (ASTM) in support of their recommended standard for limiting human exposure to ozone. The reported biological effects range from dryness of mouth and throat, coughing, headache, and chest restrictions at concentrations near the recommended limit, to more acute problems at higher concentrations.
The recommended ambient ozone exposure levels have been proposed by the Occupational Safety and Health Administration (OSHA), the American National Standards Institute/American Society for Testing and Materials (ANSI/ASTM), the American Conference of Governmental Industrial Hygienist (ACGIH), and the American Industrial Hygiene Association (AIHA) as follows:
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Control occupational exposure such that workers will not be exposed to ozone concentrations in excess of a time weighted average of 0.2 mg/m3 (0.1 ppm by volume) for eight hours or more per workday, and that no worker be exposed to a ceiling concentration in excess of 0.6 mg/m3 (0.3 ppm by volume) for more than 10 minutes. These recommended limits for ozone concentration are higher than the concentrations at which ozone can typically be smelled. Generally, an individual can detect ozone at concentrations ranging from 0.02 to 0.1 mg/m3 (0.01 to 0.05 ppm by volume). The more often a person is exposed to ozone the higher the required concentration for detection.
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Electrostatic Precipitator Ozone Safety
An electrostatic precipitator creates appreciable amounts of ozone due to the nature of its operation. High Voltage, negatively charged discharge electrodes create a corona discharge within a confined area between two positively charged collecting electrodes (gas passages). When this occurs in the presence of oxygen ozone is created. After the precipitator has been off-line for repairs or a unit outage, it is a common practice to "air-load" the precipitator to ensure that it is ready for service and free of grounds or other problems before the unit is brought back into operation. Many times work can still be in progress throughout the unit and its auxiliaries. If this is the case make sure that all personnel are out of the flue gas areas and stack downstream of the precipitator and that all access doors are closed before an electrical air load test is performed. This is also true of the immediate ductwork upstream of the precipitator. Levels of ozone produced during the air load test can be very high. Whenever there is a possibility that ozone will affect any personnel conducting operations in adjacent areas, the use of a continuous monitor, with an audible alarm is recommended. This monitor (monitors) should be placed in the work area at a level that will allow it to measure air concentrations at the workers' breathing zone. As with all aspects of industrial operations, safety should always be the first consideration.
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