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Engineering Controls Database

Local Exhaust Ventilation Systems in Printing Operations

Press operators and other workers in printing establishments are exposed to airborne solvent vapors generated when the press is cleaned. Press-cleaning solutions are generally a mixture of chemicals that include various solvents, some of which are carcinogens. Many of these solvents can be absorbed through the skin. Inks used in commercial printing are also potentially hazardous. In a study of printers’ inks, 29 samples of ink contained 46 different solvents in various combinations. Airborne exposures to hazardous chemicals are caused by evaporation from ink trays, rollers and blankets blending and thinning operations, and plate, blanket, screed, and press cleanup. Also, airborne particulates are generated by the printing process. The anti-offset powder used to prevent transfer of ink from the previous sheet to the back of the next sheet, typically made from corn or potato starch, has severe indices of ignition sensitivity and explosion severity, although the minimum explosive concentration (30±50 g/m3) is several orders of magnitude above the airborne concentrations expected in printing applications. Potato starch has a Class 2 flammability rating, characterized by local combustion of short duration.
Adverse health effects from inhalation of or skin contact with cleaning solutions include dermatitis, itchy eyes, headaches, nausea, vomiting, dizziness, respiratory failure, central nervous system depression, coughing, difficulty breathing, upper respiratory tract irritation, chest pains, unconsciousness, and death. Chronic effects may include kidney and liver damage. The principal adverse health effect of the great majority of the cleaning compounds is narcosis. The anti-offset powder used, typically consisting of raw ground corn or potato starch, is a potential allergic sensitizer. After long-term exposure, allergies to this dust could develop into occupational asthma.
Local exhaust ventilation (LEV) systems are designed to improve the control of volatile press emissions. The LEV system will take up vapor-laden air from the presses, vent it outside the building, and bring in outside air. The system consists of a fresh air supply unit having an air-to-air heat exchanger to minimize the cost of conditioning the makeup air and an exhaust hood with associated duct work to remove contaminated air from the vicinity of the hood. Any source of draft near the presses should be avoided, because it will reduce the capture efficiency of the LEV system. The ducts used for the system should be smooth on the inside and have a circular cross-section. This minimizes dust accumulation in the duct and resistance to air flow. Also, round ducts withstand larger negative pressures, and can be cleaned, in contrast to most flexible, corrugated, or rectangular ducts. The duct should be sized to maintain at least 3000 feet per minute air velocity in the duct to prevent settling and accumulation of the anti-offset powder inside horizontal duct runs. There should be a dust filter at the inlet to the fresh air system to protect the air-to-air heat exchanger from degradation caused by dust accumulation.

Photograph of local exhaust ventilation attached to the delivery end of a printing press

Photograph of local exhaust ventilation attached to the delivery end of a printing press

Local exhaust ventilation for small printer

Local exhaust ventilation for small printer
205-12-A; 205-13-A;
commercial printing
lithographic printing
press cleaning
press operator
The smoke tube results showed that apparently, any airborne material released near the working parts of the press was captured by the LEV system attached to the press. This expectation was confirmed by the real-time vapor and dust measurements, which showed reductions of 83 percent and 67 percent, respectively. The charcoal tube data also showed reductions in additive exposures of 73 percent for the press operators and 86 percent in the press area, in general agreement with the above results. Originally, in terms of health effects, the press operators’ additive exposures were near, but below, 50 percent of the estimated additive limit. After installation of the controls, the additive exposures were less than 25 percent of the limit.