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Engineering Controls Database

Control of Exposure to Perchloroethylene in Commercial Dry Cleaning by Substitution

Perchloroethylene (PERC) is the most commonly used dry cleaning solvent. PERC can enter the body through respiratory and dermal exposure.
Symptoms associated with PERC exposure include: depression of the central nervous system; damage to the liver and kidneys; impaired memory; confusion; dizziness; headache; drowsiness; and eye, nose and throat irritation. Repeated dermal exposure may result in dry, scaly and fissured dermatitis.
Whenever a substance is found to be hazardous to health or to the environment, standard industrial hygiene practice dictates that a less dangerous material or process should be considered. Extensive work has been done to find a PERC alternative. Finding an effective substitute is difficult because many of the chemicals that potentially could be used fall under one of several classes, each having physical properties that make them toxic, flammable, hazardous to the environment, or technically unsuitable for cleaning garments.

Wet cleaning:
Several studies report that 30% to 70% of garments dry cleaned using PERC can be wet cleaned satisfactorily while controlling fabric deterioration and shrinkage. Water tends to swell natural and hydrophilic fibers, but solvents have minimal effect on the properties of fibers. When natural and hydrophilic fibers swell, they can wrinkle, shrink, and lose their shape and strength. In general, the higher the synthetic content of the garment, the lower the risk of shrinkage. Machine wet cleaning can have minor variations, but most techniques are similar in that they all use specially formulated wet cleaning detergents and spotting agents, increased extraction of water before drying, close monitoring of heat and moisture content during the drying process and lower level of mechanical action during washing.
Garments are washed with varying levels of mechanical action based on garment type and amount of soiling. The greatest risk to the garment occurs during drying. Many fibers can be fully dried with little or no difficulty. However, delicate garments or those susceptible to high shrinkage must be dried for only a few minutes before being hung to air dry in the shop. Because of these problems, most wet-cleaned garments require more finishing work than garments cleaned with solvent. Long drying times and more finishing work substantially add to the required processing time.
Advantages of Wet cleaning
• Fewer health and safety hazards
• Soil contamination and large emissions of air pollutants eliminated
• More pleasant smell than solvent
• Some soils are more easily removed (i.e. sugars, salts, drinks, body fluids, starch, and milk)
• Comparable cost to cleaning with PERC
• Burden of strict health, safety, and environmental regulations reduced
Disadvantages of Wet cleaning
• Not currently a complete replacement for cleaning with PERC
• Potential for fabric deterioration, structural surface changes, felting, loss of luster and shape, dye transfer or color change
• Wools, silks, and rayons are more subject to fiber shrinkage or bleeding of dyes
• Greases, oils, waxes, and resins are more difficult to remove
• Large quantities of contaminated wastewater
• Labor-intensive, requires highly skilled workers
• Presents additional ergonomic risks to workers because it is more labor intensive

Petroleum-based dry cleaning:
Petroleum-based solvents are flammable; PERC is not. Petroleum-based solvent vapors are fuels that can burn if they are present in concentrations between the lower explosive limit (LEL) and the upper explosive limit (UEL) with sufficient oxygen. If the concentration of petroleum-based solvents in air falls below approximately 8 percent, flames will extinguish. When sufficient petroleum-based solvent vapors and oxygen are present, a fire can begin if an ignition source is present.
Petroleum-based solvents with higher flashpoints and inherently safer machines are now on the market. These solvents have flashpoints higher than 55°C/131°F and are thermally stable at operating conditions. Petroleum-based dry cleaning machines have had several technical advances to improve machine safety and reduce the risk of fire and explosion. These advances include vacuum technology, inerting with nitrogen, and better control of machine operating parameters. The following measures can be taken either in combination or separately:
• Use of an inert gas such as nitrogen or argon to displace oxygen and ensure that the oxygen concentration is sufficiently low to prevent combustion (approximately 8 percent).
• Operation under a vacuum to remove oxygen and lower its concentration <8 percent).
• Ensuring that the LEL is not exceeded, or if the LEL is not known, ensuring that the operating temperature remains 15°C below the flash point.
• Ensuring that the vapor concentration remains below 50 percent of the LEL by controlling operating temperatures or providing sufficiently high airflow.
Advantages of Petroleum-Based Dry cleaning
• Generally considered less toxic than PERC based upon exposure limits. Toxicological properties not as well documented as PERC.
• Because the vapor pressures are lower than PERC, exposures due to inhalation are generally lower
• Established cleaning solvent that is effective at cleaning all types of garments
• Generally less expensive than PERC
Disadvantages of Petroleum-Based Dry cleaning
• Presents fire hazards; PERC does not. Fire codes may limit where some shops using these solvents may be located.
• Better living condition for bacteria growth. Bacteria cause the garments to retain unpleasant odors.
• Lower vapor pressures result in a longer drying process than ERC.
• Less effective at removing oil and grease stains than PERC
• Higher insurance premiums than with PERC

Liquid Carbon dioxide:
Liquid Carbon Dioxide (CO2) is a recently developed technology that became commercially available in 1998. Many of the details concerning this technology are not available. Liquid carbon dioxide has been used for cleaning in other processes for several years. CO2 would be formulated with additives by a gas manufacturer and delivered to drycleaners in pressurized canisters.
During the process, clothes are immersed in liquid CO2 in an enclosed cylindrical basket (inside a pressure vessel that is under pressures of 700 to 1,000 psig). The load is then agitated inside the basket by high velocity fluid jets or mechanical action to remove soils. Once the cleaning process is finished, the pressure vessel is decompressed, liquid CO2 is vaporized and the dry garments are removed.
Manufacturers indicate that because liquid CO2 has a low viscosity, better cleaning is possible because smaller particles can be removed from the surface with less redeposition. Liquid carbon dioxide is a nonpolar solvent that is most effective at removing nonpolar soils such as oil and grease. While experimental laboratory studies on soil removal from garments in liquid CO2 appear promising, they have not yet been demonstrated under commercial conditions.
Advantages of Liquid CO2
• Environmental concerns such as soil contamination, air pollution, etc. eliminated.
• Shorter expected cycle time than with conventional dry cleaning, reduced garment pressing time.
• Potentially more effective in cleaning suede, leather, and fur than with conventional dry cleaning.
• Relatively high PEL of 5,000 ppm
Disadvantages of Liquid CO2
• Potential safety hazards--high pressure system, asphyxiation
• Questions regarding garment redeposition of stains that have been removed
• Possible problems removing protein stains such as grass, lipstick, or chocolate
• Possibly more expensive than PERC machines
• Very new technology for garment cleaning applications that has not stood the test of time
201-11A; 201-12A; 201-13A; 201-13B; 201-14A; 201-15A; 201-16A; 201-17A; 201-18A; 201-19A; 240-11; 240-12; 240-13; 240-14; 240-15; 256-16B; 256-17B; 256-18B; 256-19B;
NIOSH [1997]. NIOSH Report: Control of health and safety hazards in commercial drycleaners: chemical exposures, fire hazards, and ergonomic risk factors. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. DHHS (NIOSH) Publication No. 97-150.
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