Author(s): Nancy Pearce. Published on March 5, 2014.

THE DRY CLEANING INDUSTRY in the U.S. can be traced back to the late 19th century, and while the basic principle has remained the same — using solvents to remove soil from fabrics that do not withstand saturation with water — the equipment and chemicals used in dry cleaning have changed considerably. Those advances, along with the evolution of NFPA 32, Dry Cleaning Plants, have resulted in an industry that is far safer than that of its predecessors.

While early changes in the industry were largely in response to fire hazards, more recent changes are primarily due to environmental regulations. These regulations require the industry to minimize or eliminate perchloroethylene, or perc, one of the most common solvents used in dry cleaning today. While it was likely not the intent, in some cases the strict regulations on the use of perc have driven the dry cleaning industry back to the use of more combustible solvents. Since dry cleaning equipment is expensive and is listed for the use of a particular solvent, some dry cleaners have questioned if it is possible to safely convert machines approved for one solvent into machines approved for another.

The technical committee responsible for NFPA 32 recognizes the changes in the industry and is in the process of updating and revising NFPA 32 to address new technology and solvents. At the same time, the committee seeks to retain and consolidate requirements for older dry cleaning machinery into a single chapter to better differentiate between the stricter requirements needed for older technology versus newer technology. The 2016 edition of the standard will distinguish the different types of equipment and the new solvents being introduced into the dry cleaning market. The First Draft meeting was planned for late February; for updates on the standard, visit the document information page online at

Solvents and equipment
Dry cleaning is used in place of household laundering for fabrics that do not tolerate water and that could shrink or become damaged in a conventional wash. Additionally, normal household laundering may not be able to remove stains that are not water-based, which may require solvents to treat them. The term “dry cleaning” is a bit of a misnomer; while it doesn’t use traditional soap and water to clean, it does use liquids, primarly various solvents, that are circulated through the clothing, dissolving grease and oils. The mixture is removed, distilled, and filtered so that the clean solvent can be reused. According to industry sources, modern dry cleaning machines can recover and reuse more than 90 percent of the solvent.

For decades, the solvent of choice in the industry was perchloroethylene, a chlorinated solvent that emerged in the 1950s and 1960s as an alternative to petroleum-based — and often highly combustible — solvents. Perc cleaned effectively and was considered nonflammable; it had no listed flashpoint.

As perc all but eliminated the industry’s fire hazard, though, concerns grew over its potential environmental and health impacts. Perc is categorized by the Environmental Protection Agency (EPA) as a likely carcinogenic in humans, though the EPA does not believe that wearing clothing that has been cleaned with perc poses a cancer risk. The EPA is also concerned with releases of perc to the air from “fugitive emissions” — releases of the chemical as a result of clothing transfers, leaks in machinery seals, or poorly sealed containers — and to the soil and water from spills, leaks, and improper disposal. Perc does not deplete the ozone layer, but the breakdown of the chemical in the air could produce small amounts of ozone-depleting byproducts. The environmental concerns and increasing government regulations led to requirements for closed systems that recirculate the solvent, as opposed to the older “transfer” machines, where clothing wetted with perc is transferred manually to a dryer, allowing the chemical to escape into the air.

Despite advancements leading to lower perc emissions, increasing federal and state regulations have prompted the industry to look at alternative solvents and alternative methods of dry cleaning — a significant technological shift with important ramifications for NFPA 32. While this has led to innovative new technologies, including the use of wet cleaning methods that use no solvents, it has also in some cases led the industry away from nonflammable solvents and back to its roots: the use of combustible solvents, including high-flashpoint hydrocarbons, acetal, propylene glycol ethers, and siloxanes. Many of these replacement solvents, while considered less toxic than perc, include flashpoints ranging from 140 degrees F to 171 degrees F (60 degrees C to 77 degrees C).
As with solvents, dry cleaning machinery has also evolved over time. There have been four “generations” of machines, all of which are still in use in the United States. The first generation of equipment, used almost exclusively until the late 1960s, had separate washers and dryers that required the operator to manually transfer the clothes between the two. Second-generation machine design eliminated the stand-alone dryer and combined both washing and drying into a single machine. The third generation machines, introduced in the late 1970s and early 1980s, added control technology to reduce vapor emissions. The design of fourth-generation machines modifies the previous generation by recycling the air in the machine to further reduce emissions.

Modern dry cleaning equipment can be expensive, ranging between $30,000 and $65,000 per machine; a typical corner dry cleaner may have two of these machines. Many cleaners do not have the financial resources to replace old equipment. Some cleaners have asked if it is possible to switch the solvent used in the perchloroethylene dry cleaning machines rather than purchase entirely new equipment. As the committee has noted in the standard, switching from one solvent to another, even within the same solvent class, is not necessarily safe.

Dry cleaning equipment is specifically listed for a particular solvent. Changing the solvent used in a particular machine could change the solvent vapor pressure under normal operating conditions, possibly exceeding the safe operating pressure of some equipment. Additionally, changes in the compatibility of the new solvent with mate­rials of construction could lead to equipment failures or to failures of specific devices on the dry cleaning equipment. Even changing to a different solvent in the same solvent class can be a problem, since the chemicals may have different physical prop­erties that can present hazards to the operators and facilities. While the modification of equipment to handle different solvents may be technically feasible, it is critical that the original equipment manufacturer or the listing agency be contacted to verify compatibility with a change in solvent. The change in solvent would be of particular concern if the proposed conversion was from a higher-class of solvent to a lower-class of solvent with more potential fire hazards.

A source of concern for the industry has been the absence of testing standards for certifying dry cleaning machinery. The most widely used standard was UL 664, Standard for Safety for Commercial Dry Cleaning Machines, Type IV, developed by Underwriters Laboratories (UL). Recently, however, UL withdrew the standard, leaving the industry without a recognized method for certifying machinery as required by NFPA 32 and by the Occupational Safety and Health Administration (OSHA). Discussions by industry groups, standards developers (including NFPA), and federal agencies, notably OSHA, appear to have a produced a solution. Last October, several industry groups — the Textile Care Allied Trades Association (TCATA), the Dry Cleaning and Laundry Institute, the National Cleaners Association, and the Halogenated Solvents Industry Alliance — along with NFPA 32’s technical committee, announced they would work with OSHA to revise and adopt appropriate international standards for certifying dry cleaning equipment so that the industry can meet the safety requirements of the Department of Labor. While it’s not clear how soon a revised standard will be in place, a statement by TCATA described the process as a “long-term project.” 

Hazard Evolution
From flammable solvents to nonflammable solvents, and back again

Modern dry cleaning dates to the 1800s, when someone spilled a petroleum-type solvent on a greasy fabric and noticed that the stains disappeared when the solvent evaporated. The first known dry cleaner opened in 1840 in Paris using turpentine to clean clothing, and by 1879 there was at least one commercial dry cleaner operating in the U.S. Dry cleaning solvents included turpentine spirits, camphor oil, benzene, naphtha, kerosene, and white gasoline. One source indicates that in 1915, the average dry cleaner used 12,000 gallons of white gasoline per year; clothing was washed and rinsed in tubs of solvent and hung up to dry.

Fires were an understandably common occurrence, and in 1922 the president of the National Association of Dyers and Cleaners offered a $100,000 prize to any chemist who could find a cost-effective nonflammable substitute for gasoline. In 1924, researchers working with W.J. Stoddard, an Atlanta dry cleaner, introduced a petroleum-based solvent with a higher flashpoint that became known as Stoddard solvent. That same year, in cooperation with the dryers and cleaners association, NFPA’s Committee on Flammable Liquids began preparing a dry cleaning standard, and the first edition of NFPA 32 was adopted in 1925.

In 1935, when flammable solvents were still the norm, there were 57,000 dry cleaning plants in the U.S., with 1,100 fires annually, according to a 1938 issue of the Quarterly of the National Fire Protection Association. (Interestingly, about 1,100 fires occurred annually from 2007 to 2011 in laundry and dry cleaning facilities, according to data gathered by NFPA’s Fire Research and Analysis Division.)According to records from the 1930s, the majority of these fires were in non-NFPA-compliant buildings that lacked required sprinklers, and two-thirds of the facilities used gasoline or naptha as cleaning solvents. A 1936 fire in a fur cleaning and dyeing plant killed five people and injured five others.

By that time, though, fire hazards associated with the use of flammable dry cleaning agents were clearly recognized, and a wave of change had already begun. The first regulatory requirement to significantly impact the industry had come in 1928, when the U.S. Department of Commerce required dry cleaning solvents to have flashpoints above 100 degrees F (38 degrees C). This led to the introduction in the 1930s of trichloroethylene (TCE) and perchloroethylene, or perc—chlorinated solvents that provided the same cleaning properties as petroleum-based products but were nonflammable. Percholoroethylene, in particular, became popular during World War II when petroleum was in short supply.

Even so, the use of petroleum-based dry cleaning solvents persisted throughout the 1940s and 1950s. The fire and explosion hazards associated with dry cleaning plants—most of which still used combustible solvents, including Stoddard solvent — were considered so extreme that by 1957 most insurance companies would not issue policies for them.

The industry got the message. By the 1960s, perc had become the solvent of choice in most dry cleaning facilities nationwide. The chemical remains the primary dry cleaning solvent in use today — though health and environmental concerns have led to significant regulation of perc, as well as to the development of alternative and less-toxic (though more-combustible) solvents. Technological advancements have further increased the efficiency of dry cleaning systems using perc. In 1975, 8,000 pounds of clothing could be cleaned with one 55-gallon drum of the chemical. Today a 55-gallon drum of perc can clean up to 55,000 pounds of clothing.


An evolving standard
The requirements in the current edition of NFPA 32, issued in 2011, are primarily dependent on the type of solvent used within the location. Four classes of solvents — Class I, II, IIIA and B, and IV — are defined in the standard, with definitions of the Class I, II, and III solvents mirroring those found in NFPA 30, Flammable and Combustible Liquids Code. Class IV solvents are those not covered by NFPA 30, such as perc, trichloroethylene, or other solvents that do not have flashpoints measurable by standard test methods. The standard defines dry cleaning plants in terms of the solvent system used, meaning a Type 1 plant utilizes a Class 1 solvent, a Type II plant utilizes a Class II solvent, and so on. (It should be noted that while Class I solvents are defined, Type I plants employing these solvents are prohibited in the standard; Class I solvents are for spotting or pre-spotting only, and are allowed in limited quantities in approved containers.)

The standard also provides some general plant requirements, with specific requirements for each of the plant types provided in dedicated chapters. Type II dry cleaning facilities using a Class II solvent, for example, are detailed in a specific chapter, in addition to the general chapter requirements for all systems. Those general requirements include employee training, lint and refuse removal, spill and leak prevention, and building construction.
The Technical Committee on Textile and Garment Care Processes has undertaken a considerable rewrite of the 2016 edition of the document to simplify its requirements and to reflect current technology and solvent use. When the standard was first developed, for example, the only solvents in use were Class II solvents. The equipment required large quantities of solvent and emitted combustible vapors that were not well contained. Recycling and reuse were not typical aspects of operation. Most drycleaning was done in large facilities, which is why the document’s title refers to drycleaning “plants.”

When perchloroethylene, a Class IV solvent, was introduced, much of the industry moved away from the large plants and into the smaller neighborhood facilities common today. These changes, along with the multitude of new, more environmentally friendly solvents that have emerged in the wake of concerns over perc, are just some of the topics that will be addressed in the new edition of NFPA 32.

The requirements of the new document will be based not only on the class of solvent, but also on equipment. The revised standard will better identify the type of equipment to be used with a particular solvent to make it clear to AHJs what type of facility fire protection is required. For example, the revised standard will recognize the differences between closed-loop and open-circuit systems; closed-loop systems will have fewer fire protection requirements than open-circuit systems, since there is less chance for the creation of fugitive emissions.

The standard is also expected to expand the facility maintenance requirements, as well as the training and work practices for employees. Building construction requirements may also be modified to take into consideration the type of solvent and equipment used. Finally, a new chapter will be added to differentiate between Type IV machines using perchloroethylene and Type IVA machines that use solvents such as carbon dioxide. While there are existing storage requirements for the use of liquid carbon dioxide, requirements for the safe use of carbon dioxide in dry cleaning do not currently exist. The revised standard will help distinguish between equipment covered by existing standards and equipment that is not.

The dry cleaning industry will continue to change as newer solvents, equipment, and cleaning techniques are developed. The future of the industry may look very different than it does now, with more of an emphasis on wet cleaning; significant research is being done on the use of water and biodegradable detergents for clothing that would normally require dry cleaning. Whatever replacement techniques or solvents are selected, they must clean effectively, be reasonably priced, and be environmentally friendly and safe for humans. The fire safety of those products will also be a major consideration as alternative methods and machinery are introduced, ensuring that NFPA 32 will continue to play a critical role in the evolution of this dynamic industry.

Nancy Pearce, staff liaison for NFPA 32, is a certified industrial hygienist and senior fire protection engineer at NFPA.