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ReplacingReplacing 1,1,1-Trichloroethane1,1,1-Trichloroethane WithWith OtherOther ChlorinatedChlorinated SolventsSolvents By Vicki L. Rupp & Janet C. Hickman

Cleaning and degreasing metal production stage. The process is cost- scheduled for phaseout, and are not parts before plating or coating is an effective and energy-efficient, and has subject to the excise taxes levied on important step in the manufactur- a small floor-space requirement. In ODSs. Despite their similarity to ing process. For a large percentage addition, the has excellent TCA, these alternate also of companies, and for a long time, cleaning capacity for greases and oils, have certain characteristics of their this has meant vapor degreasing and is not likely to cause rust damage. own that make them particularly with 1,1,1-trichloroethane (TCA, It has low toxicity, a high permissible suitable for specific types of also known as methyl or exposure level (PEL), is not flam- degreasing. MCF). Times are changing, how- mable under most conditions, and is ever. Production of TCA for listed as a non-volatile organic Methylene Chloride (MEC) emissive applications, such as compound (VOC). Consequently, for MEC (also called degreasing, ceases in all developed a number of years TCA had virtually and methylene dichloride) is a countries as of the last day of 1995, replaced most other solvents for the powerful and versatile chlorinated leaving many manufacturers in a vapor degreasing process, as well as solvent known for its high solvency quandary. Until recently, the Dow for cold cleaning and electronic capabilities. It has a mild ethereal Chemical Company, Midland, MI, cleaning. and is completely miscible with was the only U.S. chemical pro- Under the U.S. Clean Air Act a variety of solvents. ducer to manufacture a complete Amendments of 1990, however, as A clear, heavy liquid (10.98 lb/gal), line of chlorinated solvents, includ- well as the international Montreal MEC has the lowest ing TCA and tetrachloride, Protocol, TCA was classified as an (103.5 °F; 39.8 °C), the lightest vapor which have been implicated in the -depleting substance (ODS) and (2.93 times that of air), and depletion of the stratospheric ozone is scheduled for production phaseout the highest solvent power of the layer. As of April 1994, the company for all emissive applications by chlorinated alternatives. It freezes at discontinued the production of December 31, 1995. In view of this -139 °F (-95 °C). TCA. Dow and other suppliers requirement, many users of the With its low boiling point and high continue to actively pursue answers solvent have been converting to solvent power, MEC is well suited for to the solvent alternatives problem. substitutes or alternatives. cleaning temperature-sensitive parts, such as thermal switches and ther- lthough recycled TCA and The Search for Alternatives mometers, and for removing tough TCA from inventories will Unfortunately, good alternatives are paint residues, hard-to-dissolve resins, A still be available after hard to find. Those based on a and gross metal fines. It can be also January 1, 1996—and although different, non-chlorinated chemistry used effectively on white metals manufacturers in developing coun- often require considerable testing, (aluminum and ). In vapor tries are permitted an extension of plus costly re-engineering. Although degreasing, its low boiling point and several years on the phaseout—the there are no exact “drop-in replace- ability to dry quickly have permitted great majority of users are actively ments,” the closest alternatives are the high throughput at an acceptable cost. seeking a replacement for the solvent. other three readily available chlori- On the other hand, the high Fortunately, the Significant New nated solvents—methylene chloride solvency of MEC may be too aggres- Alternatives Program (SNAP), (MEC), perchloroethylene (perc or sive for some substrates, such as published by the U.S. Environmental PCE) and trichloroethylene (TCE). plastics and rubber. Further, because it Protection Agency (EPA) in March These three solvents share most of passes rapidly into the vapor phase, it 1994, has brought a long-needed the advantages of TCA, such as: is difficult to contain the vapor. When solution to the problem: Maintain the converting a degreasing system from vapor degreasing process while • Excellent solvency TCA to MEC, chillers are required to replacing TCA with one of the other • Virtually non-flammable contain the vapors, and a lip-vent chlorinated solvents. • Low toxicity when used in exhaust or vapor-removal device may accordance with established be necessary. The heat input should be TCA—Formerly safety procedures. reduced and carefully controlled to The Solvent of Choice prevent too much agitation in the The benefits of degreasing with TCA In addition, these solvents have not boiling solvent. The engineer in are well known. Parts leave the been implicated as sources of strato- charge of surface cleaning should degreaser dry and ready for the next spheric , are not determine whether tighter equipment

34 PLATING & SURFACE FINISHING is required, or whether a retrofit is Table 1 needed to minimize emissions. OSHA Permissible Exposure Limits (PELs) Perchloroethylene (PCE) Solvent 8-hr time-weighted Short-term exposure PCE or perc (also known as average (TWA)—ppm (STEL)—ppm ) is a clear, colorless liquid with a distinctive, Methylene Acceptable ceiling somewhat ether-like odor. Physical chloride 500* concentration: 1000 properties of PCE include: Maximum acceptable peak: 2000* • Boiling point: 250 °F (121.1 °C) Perchloro- 25** — • Freezing point: -9 °F (-22.8 °C) • Vapor density: 5.76 times that of air Trichloro- 50** 200** • Weight: 13.47 lb/gal ethylene 1,1,1-trichloro- 350 450 With the highest boiling point of ethane the chlorinated solvents, PCE is excellent for removing heavy grease *Currently under rulemaking to lower the PEL; 25 ppm has been proposed on an 8-hr and high-melt waxes. It also easily TWA, with a STEL of 125 ppm. removes moisture from wetted parts. **These limits in OSHA’s 1989 rule have been overturned. With its high solvent power, it provides extensive cleaning action. Table 2 PCE is recyclable and can be ACGIH Threshold Limit Values readily recovered by carbon adsorp- tion methods. It can also tolerate Solvent 8-hr time-weighted Short-term exposure relatively large quantities of water average (TWA)—ppm (STEL)—ppm without degrading. Because it vaporizes at a higher temperature than Methylene 50 — the other chlorinated solvents, chloride however, higher utility costs are Perchloro- 25 100 required for heating the solvent to ethylene vapor level and for cooling chill water Trichloro- 50 100 above the vapor level in the degreaser. ethylene In addition, when cleaned parts are 1,1,1-trichloro- 350 450 removed from the degreaser, they ethane must be allowed to cool before they can be handled.

Trichloroethylene (TCE) Because of its excellent cleaning well-documented exposure guidelines TCE is a clear, heavy liquid (12.11 lb/ properties and high solvency, TCE has and safe handling procedures. gal) with excellent solvency. Non- been considered the universal vapor- Exposure to vapor concentrations corrosive and easily recycled, TCE degreaser solvent. It is commonly within recommended guideline levels boils at 189 °F (87 °C) and freezes at used in vapor degreasers, is recy- will not result in any known adverse -124 °F (-86.7 °C). The high density clable, dries quickly and has low effects on most people. Acute over- of TCE’s vapor (4.53 times that of air) energy requirements. exposure to vapors, however, may assures low vapor loss and easy Conversion from TCA to TCE is cause or narcotic effects recovery from vapor degreasing fairly straightforward. Heat in the (known as solvent drunkenness), systems. Carbon adsorption recovery is degreaser should be increased to 15 lb central nervous system effects, and often used with TCE to trap emissions. of steam, or equivalent electric or liver and/or kidney problems. Because At one time, TCE had been the heat input, and all possible methods chlorinated solvent vapors are heavier preferred solvent in the metal finish- of emission reduction should be used than air, very high concentrations can ing industry, but numerous state and to meet the lower PEL. Regular vapor accumulate in poorly ventilated areas. local environmental regulations now monitoring is suggested to help keep Exposure to such concentrations can classify it as a VOC. As a result, it the workplace within Occupational cause dizziness, unconsciousness, and had been widely replaced with 1,1,1- Safety and Health Administration even death. trichloroethane, although TCE (OSHA) limits. Small amounts of chlorinated remained in use for specialty applica- solvents that might be ingested tions, such as stripping semi-cured Health Profile inadvertently are not likely to cause varnish or paint films and removing One major benefit of chlorinated injury. Ingestion of larger amounts, heavy rosins and buffing compounds. solvents is the extensive study that however—accidentally or intention- With the phaseout of TCA, however, has been done on their safety and ally—could result in serious injury or and the impetus of EPA’s SNAP health effects. Extensive laboratory death. Occasional, brief skin contact ruling, trichloroethylene is making a and epidemiological studies have with chlorinated solvents is not likely comeback. been made, and these have resulted in to produce any significant adverse

December 1995 35 effects, nor is a single, prolonged 1989, OSHA proposed a downward EPA’s SNAP Rule exposure likely to result in absorption revision of the workplace PELs for a EPA’s new SNAP rule gives industry of harmful amounts through the skin. number of substances, including the official go-ahead to consider The solvents can de-fat the skin, perchloroethylene and trichloro- MEC, PCE and TCE as acceptable however, which can cause dermatitis ethylene. alternatives to TCA. Published on to develop, especially when there is This ruling was overturned in 1992 March 18, 1994, in the Federal frequent gross daily contact. by the U.S. Court of Appeals for the Register (59 FR 13044-13161), the In February 1995, the International Eleventh Circuit, sending workplace rule applies to the uses of TCA in Agency for Research on Cancer standards back to the limits set prior surface cleaning, , adhesives, (IARC) reclassified perchloroethylene to 1989, at least until OSHA could coatings and inks. and trichloroethylene to Category 2A develop a new standard. Dow recom- At the same time, EPA expresses (probably carcinogenic to humans). mends controlling exposure to the concern about worker exposure and PCE previously had been classified in chlorinated solvents below OSHA’s environmental emissions if these Category 2B (possibly carcinogenic to 1989 PELs, or the ACGIH guidelines, solvents are not used and controlled humans), and TCE in Group 3 (not whichever is lower. properly. They advise that the three classifiable as to carcinogenicity in The chlorinated solvents are chlorinated solvents should only be humans). The reclassification was practically non-flammable, because used in accordance with other based on the conclusion by the IARC they have no flash point or fire point environmental, workplace and panel of experts that laboratory as determined by standard test consumer regulations. (See accompa- studies provided sufficient evidence methods. Methylene chloride and nying sidebar.) of carcinogenicity in animals, and that trichloroethylene, however, do have a epidemiology studies provided limited flammable range when high concen- Conversion Checklist evidence of carcinogenicity in trations of vapors are mixed in air and Anyone planning to use MEC, PCE or humans. The experts, however, were exposed to a high energy source. TCE as replacements for TCA in a not unanimous in their decision. Perchloroethylene has no flammable vapor degreasing process should be It should be stressed that this IARC mixtures in air. Lower and upper careful to observe the following evaluation is one of cancer “hazard,” flammability limits for methylene procedures: not “risk.” While hazard reflects the chloride in air at 77 °F (25 °C) are 14 intrinsic properties of a product, risk to 22 percent, while the flammable 1. Prior to conversion, be sure to represents the possible health impact range of trichloroethylene runs from 8 obtain state and/or local air permits from exposure levels in practice. The percent to saturation, with the (VOC and air toxics), arrange IARC decision is not expected to have saturation point increasing with waste disposal complying with all significant impact on users of PCE or temperature. At 100 °C, the upper appropriate regulations, and make TCE, provided appropriate safe- is 44 percent. provisions to control worker handling precautions are observed. It Before analytical methods were exposure to solvent vapors below is The Dow Chemical Company’s developed to detect chlorinated the OSHA PEL standard. contention that the solvents can be solvents in parts-per-million (ppm) 2. Drain and clean the degreaser. used safely, as long as users follow and smaller quantities, it was consid- Solvent must be removed com- the recommended exposure limits, ered safe to dispose of solvent wastes pletely to avoid instability from which were established by taking into in . Such practices are no mixing solvents. Entry into the account the relevant data on both longer acceptable. Today, the pre- degreaser should be avoided. If hazard and risk. ferred method of disposing of solvent entry is required, it is critical to When IARC’s monograph is waste is to send the material, via a follow a confined-space entry officially published, the producers of permitted waste-hauler, to a licensed procedure, such as described in the solvents are expected to make reclaimer or a permitted incinerator, ASTM Standard D4276. appropriate changes to the material in compliance with federal, state and 3. If the existing solvent in the safety data sheets (MSDSs) and labels local regulations. Most states and the degreaser has gone acid, consult for perchloroethylene and trichloro- federal government now have regula- the solvent supplier for special ethylene. In addition, both the tions for the disposal of solvent wastes. cleaning procedures. producers and their trade associations To promote the safe use and 4. Adjust the vapor safety thermostat will investigate the need for addi- responsible handling of products in to activate (i.e., to turn off the heat tional research and independent the chlorinated solvent family, U.S. supply) when contacted by solvent reviews of existing and new labora- producers of chlorinated solvents vapors. tory and epidemiology studies. participate in the Responsible Care® 5. Adjust the boiling sump thermostat initiative of the Chemical Manufac- to activate at the approximate boiling Safety Guidelines turers Association, including the temperature of the new solvent with Permissible exposure limits (PELs), initiative’s extensive product and 25–30 percent mineral oil content. set by OSHA (Table 1), and recom- environmental stewardship provisions. 6. Prior to initial start-up: mended threshold limit values This includes providing customers with A. Review the MSDS (TLVs), established by the American safety, handling, storage, and disposal B. Label the degreaser appropriately Conference of Governmental Indus- information, MSDSs, regulatory and trial Hygienists (ACGIH) (Table 2), environmental information. In addition, ______have been in force for chlorinated they may provide product literature and Responsible Care® is a registered service mark solvents for a number of years. In videotape training presentations. of the Chemical Manufacturers Association.

36 PLATING & SURFACE FINISHING Table 3 cover both vapor degreasing and cold Recommended Equipment Settings* (or immersion) cleaning with trichloroethylene, perchloroethylene, Solvent Vapor safety Boiling sump Operating steam methylene chloride and chloroform, thermostat (°F) thermostat (°F) pressure (psig) as well as with 1,1,1-trichloroethane and carbon tetrachloride, which are Methylene 95 108 <2 scheduled for phaseout as of the end chloride of 1995. The goal of the NESHAP is Perchloro- 180 257 45–60 an overall reduction in solvent ethylene emissions of 50–70 percent of current Trichloro- 160 193 10–15 nationwide emissions. ethylene Recognizing the great variety of 1,1,1-trichloro- 130 172 1–6 industries using chlorinated solvents ethane for cleaning, as well as the number of different applications and operating *Note: While these are recommended equipment settings, users should always first con- procedures, EPA has provided for a sult with the machine manufacturer and current product literature before operating any variety of options that companies can machine. select to comply with these regula- tions. At the same time, the standards, which are set out in the Federal Register, are very complex. 7. Close all drains. Charge the The Degreasing NESHAP Among other requirements, the degreaser to normal levels and Emission standards for chlorinated NESHAP lists a number of control start-up according to standard solvent degreasing operations are now procedures. Various combinations of operating procedures. governed by the new National these can be used to achieve the 8. Monitor worker exposure to ensure Emission Standards for Hazardous Air required vapor emission limits. The PELs are met. (NESHAP) for new and user should consult Federal Register, 9. For equipment adjustment, see existing halogenated solvent cleaning Vol. 59, No. 231, pp. 61801–61820. Table 3 for thermostat and steam operations. Issued by the U.S. EPA on The control procedures listed in the pressure settings. December 2, 1994, the standards NESHAP are:

Free Details: Circle 113 on postpaid reader service card. Free Details: Circle 114 on postpaid reader service card.

December 1995 37 Freeboard ratio of 1.0—The height In addition, operators must employ About the Authors of the freeboard above vapor level automated parts-handling, as well as Vicki L. Rupp is must be equal to the width (shorter specified work practices. The parts- group leader at dimension) of the degreaser. handling system must be an auto- The Dow Chemi- Freeboard refrigeration device—A mated hoist or conveyor that carries cal Company’s refrigerated system that creates a parts at a controlled speed of 11 ft/ Chemicals cold-air blanket above the vapor min or less through the complete Technical Service zone. cleaning cycle. The work practices, & Development Reduced room draft—Wind speed which have been set to reduce department, 2020 above the freeboard must not exceed emissions, are listed in a qualification Willard H. Dow 50 ft/min (15.2 meters/min). test developed by EPA, which Ctr., Midland, MI Working-mode cover—Any cover cleaning machine operators must be 48674. She holds a BS in chemistry or machine design that shields the able to pass. from Saginaw Valley State University, cleaning machine from outside air EPA’s guidelines as listed in the and has 12 years of service with Dow. disturbances during cleaning. degreasing NESHAP provide excel- Dwell—Refers to the time in which lent guidance for the safe and respon- Janet C. cleaned parts remain in the freeboard sible use of chlorinated solvents in Hickman is area above the vapor zone after metal cleaning. Close adherence to development cleaning. EPA defines proper dwell these guidelines, as well as to other leader, chlori- time as 35 percent of the time regulations, will permit companies to nated organics, at required for the parts to cease continue using the vapor degreasing Dow’s Chemicals dripping in the vapor zone. process for high-quality cleaning of Technical Service Superheated vapor—Vapor metal parts. & Development temperature maintained 10 °F above For assistance in implementing department. She the boiling temperature of the solvent. these guidelines, one of the chlori- received her BS Carbon adsorption equipment— nated solvent suppliers will be able to from Kansas University, and has Equipment in the ventilation system help. ❏ worked for Dow for 21 years. connected with the degreaser. A Summary of Regulations Covering Chlorinated Solvents lthough the chlorinated solvents methylene chloride solvents, including annual refresher courses. Containers of A (MEC), perchloroethylene (PCE) and trichloroethylene these hazardous chemicals in the workplace, as well as con- (TCE) are not subject to phaseout as depleters of stratospheric tainers leaving the workplace, must be marked with an “ap- ozone, they are subject to a variety of other federal, state and propriate hazard warning label.” In addition, individual local regulations. Here is a summary of the major ones: states—including California, New Jersey, New York and Pennsylvania—have specific labeling requirements. The Clean Air Act Amendments of 1990 VOC Regulations Resource Conservation & Recovery Act (RCRA) TCE is controlled as a volatile organic compound (VOC), Waste containing chlorinated solvents must be considered and limitations are placed on its emissions, particularly in . It must be transported by a certified haz- ozone non-attainment areas. PCE is considered a VOC un- ardous waste hauler, stored in a licensed storage facility, and der most state regulations implementing the national ambi- disposed of in licensed treatment and disposal facilities. ent air quality standards for ozone. It does not contribute appreciably to formation, however, so the U.S. EPA is Comprehensive Environmental Response, expected to grant it exemption fromVOC regulations. MEC Compensation & Liability Act (CERCLA or ) is exempt from both federal and state VOC regulations. If a “reportable quantity” of a chlorinated solvent is released to the environment in any 24-hr period, federal, state and HAP Regulations local authorities must be notified immediately. Reportable EPA has designated the chlorinated solvents as hazardous quantities for each of the solvents are: Methylene chloride, air pollutants (HAPs). A complete set of regulations has not 1000 lb; perchloroethylene and trichloroethylene, 100 lb. been issued for their control, although a National Emission Standards for Hazardous Air Pollutants (NESHAP) has been Clean Water Act issued for cleaning with chlorinated solvents. The chlorinated solvents are defined as toxic pollutants (also Many states have enacted HAP regulations or Toxic Air called priority pollutants), and their discharges into water- Containment (TAC) regulations for lists of chemicals, which ways are regulated. Different regulatory requirements may usually include chlorinated solvents. be demanded of direct dischargers (those that discharge di- rectly into a waterway) and indirect dischargers (those that Occupational Safety & Health Administration (OSHA) discharge into a water treatment system). Hazard Communication (HAZCOM) In addition to federal requirements, state and local gov- Training on hazardous chemicals in the workplace is required ernments may have specific regulations concerning the dis- for all employees who could be exposed to the chlorinated charge of wastewater containing these solvents. ❏

38 PLATING & SURFACE FINISHING