Multi-solvent dry cleaning machine.
Multi-solvent dry cleaning machine.

Perchloroethylene (perc) remains the solvent of choice for dry-cleaners in Europe and North America, despite increasing pressure over many years to switch to alternative cleaning processes.

It and its sibling trichloroethylene (TCE) remain the solvents of choice for finishers doing solvent cleaning in North America, and even more so in Europe.

Crusaders for improved public health and green chemistry have told U.S. operators for more than two decades about the toxicity and carcinogenicity [1,2] hazards of using these solvents.

Yet more than 70% of dry-cleaning shops in the U.S. use either perc alone or in combination with other solvents.[3] And every year in the U.S., millions of feet of rolled steel sheet are degreased with TCE.

It is the same actions (or inactions) which are ongoing in managing the combustion of coal to produce electricity, or the political machinations associated with upgrading the financial security of Medicare, or the inconsistent choices we make in an effort to lose weight.

What’s going on here is human unwillingness to abandon what works well and adopt something that doesn’t work as well (and comes with a huge increment of cost).

Considerable quantitative data are available about this industry, which has close contact with the public. This has led to both voluntary changes by dry-cleaning shops, as well as regulatory action.

Testimonials of successful conversion from perc to something “green” abound on the Internet. Of course, it is usually non-franchise chain  shops that have converted.

Some cities (Philadelphia and DC) have banned the use of perchloroethylene for dry-cleaning operations. California announced in 2007 that it will phase out the use of perchloroethylene in dry-cleaning operations in 2023.

Dry-cleaners can now choose from alternative cleaning systems that are based on silicone, hydrocarbon, and liquid  carbon dioxide.
Multi-solvent machines, mostly manufactured in Europe (particularly Italy) offer the capability to use:

  • Liquid carbon dioxide at elevated pressure (with or without dipropylene glycol n-butyl ether as a surfactant),
  • The “3A” solvents used for parts cleaning in Germany,
  • High-flash aliphatic hydrocarbons (such as DF-2000),
  • Solvon K4 (1,1-dibutoxymethane) from Kreussler in Germany [4]
  • GreenEarth (decamethylcyclopen- tasiloxane, or D5, as a carrier for an unnamed surfactant),
  • Rynex (a mixture of glycol ethers)
  • DrySolv (n-propyl bromide!)

In addition, wet cleaning with water and biodegradable surfactants is gaining favor in some sectors.

At the September 2011 Clean Show in Las Vegas, equipment displayed was reported to apply only to the above alternative cleaning systems. This was reported to be a deliberate decision by manufacturers of dry-cleaning machines, despite their expectation that sales of the alternative machines would be slow.

Although these alternatives to perc have been implemented on a limited commercial scale, there seems to be no single favored technology that threatens perc in the short term.  

Does this sound familiar? Most of these alternative cleaning systems could be, or have been, used to clean parts.

I believe the following quote from the reference cited in note #3 captures the situation:

...On a global basis, the general consensus seems to be that perc has a future, as long as it remains the preferred choice for the majority of cleaners—but it would be wrong to describe it as the future of dry-cleaning...

My own (and more limited) research into cleaning operations strongly suggests the quotation above perfectly applies to the current situation in parts cleaning.

Yes, there have been conversion to non-in-kind alternatives to perchloroethylene (and trichloroethylene) for more than a decade. But if a user has thick, baked-on grease to remove from large steel gears, and is doing that with perc, it will be—and has been—difficult to convince that  user to accept a less-effective technology.

I believe the conversion in parts and textile dry-cleaning in the U.S. will proceed at a parallel (and slow) pace to where perchloroethylene is seldom used in either application. That pace may be tortoise-like, taking more than a decade to where a current user will choose to abandon perchloroethylene in favor of some alternative.

Heretofore, the market positions of perchloroethylene and trichloroethylene have been similar.

If the operator of a fabricating line, cutting sheet steel, wants to remove a rust-protective oil sprayed on at the mill, and not use a water-based product that would require application of another rust  protective coating, he or she would be doing that with trichloroethylene.

My limited research suggests that EPA’s finding trichloroethylene to be a human carcinogen (reference note #2) has not yet acted as a motivating force to users as would a foghorn to warn ships traveling too close to a rocky shore. But, the finding noted above by EPA will separate those positions in the market.

The 8-hour exposure limit for trichloroethylene may soon (two to three years) be reduced from 50 ppm (current) to 5 ppm [5](the forecast by some). That would hasten abandonment by a current user of trichloroethylene to degrease steel sheet.

I am not so optimistic. I think the 8-hour exposure limit for trichloroethylene will be 1 ppm [s6] (or less) in the same time frame.

My forecast is based on values established for other human carcinogens: benzene (1 ppm), formaldehyde (0.75 ppm), and ethylene oxide (<0.1 ppm).

So the parallels with the textile dry-cleaning industry and the parts cleaning industry will disappear because of the substantial difference in classification about carcinogenicity.

Beware of unintended consequences!

Regulators—responsibly making it more difficult for operators to use trichloroethylene—may well induce increased use of perchloroethylene as a replacement for trichloroethylene.

After all, perchloroethylene has: (1) current status by use in textile dry-cleaning, (2) a lower commodity price, and (3) it’s VOC exempt in the U.S.!

Change is: driven by many factors; hard to predict; and always imminent.

I believe the pattern of use of perchloroethylene suggests that reduction in its use in parts cleaning will be slow because of that trend in textile dry cleaning.

However, it’s not the same for trichloroethylene. U.S. EPA will shortly re-rate the 8-hour exposure limit for trichloroethylene—thereby initiating significant change in the parts cleaning industry.    

John Durkee is the author of the book Management of Industrial Cleaning Technology and Processes, published by Elsevier (ISBN 0-0804-48887). He is an independent consultant specializing in metal and critical cleaning. You can contact him at PO Box 847, Hunt, TX 78024 or 122 Ridge Road West, Hunt, TX 78024; 830-238-7610; Fax 612-677-3170; or


  1.  A legitimate source for scientific debate is the carcinogenic effect of perchloroethylene. U.S. EPA classifies perc as a “possible” carcinogen, but the pressure to change that word to the more serious “probable” classification has been ongoing for years. The International Agency for Research on Cancer of the World Health Organization (IARC) classified perchloroethylene as a Category 2B (possible human carcinogen), and the 8-hour exposure limit is 100 ppm.
  2. In September 2011, EPA made its final assessment (EPA/635/R-09/011F), which characterizes the trichloroethylene as carcinogenic to humans and as a human noncancer health hazard affecting the central nervous and immune systems, the kidneys and liver, male reproductive organs and the developing fetus. See
  3. Vince, T., “Solvents Update: Technological Advances Drive Cleaning Options,” Laundry and Cleaning News, December 1, 2011. Can be read at
  4. Durkee, J.B., “Cleaning Times: All The World is NOT Flat: Part 3,” Metal Finishing, Vol. 108, Issue 4, April 2010.
  5. The 8-hour exposure limit of 5 ppm for trichloroethylene could probably met by most enclosed or vacuum cleaning machines.
  6. The 8-hour exposure limit of 1 (or less) ppm for trichloroethylene cannot be met by most enclosed or vacuum cleaning machines.