Commercial laundries began as domestic enterprises, but have developed into businesses with many unique health and safety concerns. Laundries specializing in services for hospitals must deal with possible biological hazards, and those laundering work clothes for manufacturing or service workers may risk exposure to specific chemical hazards.
Dry cleaning reputedly originated in France in 1825 when a worker in a dye and cleaning factory spilled lamp oil on a soiled tablecloth (IARC 1995a). After the tablecloth dried, the spots had disappeared. Lamp oil is a hydrocarbon. Similar hydrocarbon solvents - turpentine, kerosene, benzene and gasoline - were used in the fledgling dry-cleaning industry. All these solvents had one major disadvantage: they were flammable, often resulting in fires and explosions (Wentz 1995). In 1928, W.J. Stoddard introduced a nearly odourless, petroleum-based solvent with a higher flashpoint, which reduced the risk of fire. Stoddard solvent gained widespread acceptance in the industry and is still used today.
At the turn of the century, advances in the synthesis of chlorinated hydrocarbons permitted development of nonflammable solvents for dry cleaning. Initially, carbon tetrachloride was preferred, but because of its toxicity and aggressiveness to metals, textiles and dyes, it was gradually replaced in the 1940s and 1950s by trichloroethylene and tetrachloroethylene (also commonly known as perchloroethylene, or PERC) (Wentz 1995). PERC (C2Cl4) is a colourless, clear, heavy liquid with an ethereal odour. Today, approximately 90% of US dry cleaners use PERC (EPA 1991a).
Although cleaning practices vary from country to country and from shop to shop, laundries and dry-cleaning shops are usually small businesses; about 70% of US dry-cleaning shops have fewer than four employees, who usually perform the cleaning at the same location as the shop. The employees of such a small business, many of whom typically labour more than eight hours per day, may be members of one family, sometimes including children. In many countries, the dry-cleaning family lives in the same building as the shop. An increasing trend among larger corporations is to operate multiple “drop” shops where customers leave soiled garments. The garments are transported to a central facility for cleaning, and later returned to the drop shops for customer pick-up. This arrangement confines hazardous waste to one site and reduces the solvent exposure of drop shop workers.
The Laundry and Dry-Cleaning Process
The dry-cleaning or laundry process usually begins when a customer brings soiled garments to a shop. Modern clothing is made from many different fibres and fabrics. Garments are inspected and sorted according to weight, colour, finish and fabric type prior to machine loading. Visible stains are treated at a spotting station with various chemicals, before or after cleaning, depending on the type of stain.
Cleaning is a three-step process: washing, extracting and drying (figure 1). Wet-process washing (laundering) uses detergent, water and possibly steam. In dry cleaning, detergent and water are added to the solvent to aid in soil removal. Clothes are manually loaded into the machine, and the cleaning solution is automatically injected. Machine contents are agitated for a period, then spun at high speed to extract the water or solvent and tumbled dry. Once garments have been removed from the dryer, they are pressed to remove wrinkles and restore their shape.
Figure 1. The dry cleaning process flow diagram.
Many countries have recently imposed stringent regulations for the control of PERC exposures and emissions because of associated health effects and environmental problems. In response to these regulations, dry-cleaning processes are changing. Improved solvent purification and vapour-recovery systems are available, alternative solvents are being developed, and wet methods using water immersion are being refined to clean garments traditionally cleaned in solvent. These processes are described below.
Transfer versus dry-to-dry equipment
Two basic types of machines used in dry cleaning are transfer and dry-to-dry. Transfer machines, older and less expensive, require manual transfer of solvent-laden clothing from the washer to the dryer. The transfer activity causes excessive worker exposure to PERC. Because of high solvent usage rates, emissions and exposures during transfer, PERC transfer machines are no longer manufactured in the United States; however, older used or reconditioned ones can still be purchased.
In 1994, at least 70% of PERC machines in the United States, for example, were dry-to-dry machines, using a one-step process that eliminates clothing transfer. Many shops are replacing or have replaced transfer machines with dry-to-dry machines because of the trend towards stricter environmental regulations; however, some shops still use transfer equipment for increased productivity and to avoid the capital expenditure required for new machines. In the United States, petroleum machines are primarily transfer units.
Dry-to-dry machines may be vented or ventless. Vented dry-to-dry machines vent residual solvent vapours directly to the atmosphere or through some form of vapour-recovery system during the aeration process. Ventless dry-to-dry machines are essentially closed systems, open to the atmosphere only when the machine door is opened. They recirculate the heated drying air through a vapour-recovery system and back to the drying drum. There is no aeration step.
Solvent purification: Filtration and distillation
Dry cleaners use filtration and/or distillation to recover and purify solvents. Filtration removes insoluble soils, non-volatile residues and loose dyes from the solvent. It is also sometimes used, primarily in the United States, to remove soluble soils. Filtration is a continuous process. The solvent passes through an adsorbent powder, cartridge or spin-disc filter, all requiring some level of periodic maintenance. Each filtration system produces contaminated cartridges or powders.
Distillation, used by 90% of US cleaners, removes soluble oils, fatty acids and greases not removed by filtration (International Fabricare Institute 1990). Distillation occurs when PERC is heated to its boiling point so that it vaporizes and later condenses back to liquid form. During this process, non-volatile impurities, which cannot be boiled off, remain in the still and are discarded as hazardous waste. Both filtration and distillation produce some solid wastes containing PERC; however, dry-cleaning machine manufacturers are striving to develop new filtration and distillation technologies that reduce the amount of hazardous waste produced. This ultimately results in important savings to the owner by reducing the cost of hazardous-waste disposal.
Recovery of PERC vapours
Two primary technologies are used to recover PERC vapours: the carbon adsorber and the refrigerated condenser. These two technologies, traditionally separate, are used together in more modern machines. Carbon adsorption is used in about 35% of the controlled machines in the United States, for example. Carbon adsorbers achieve a 95 to 99% vapour reduction by removing PERC from the air. Solvent-laden vapours pass over activated carbon having a high adsorption capacity. The carbon is later desorbed and the PERC recovered, or the carbon is discarded as hazardous waste when it becomes saturated with PERC. Carbon desorption typically occurs with steam or hot air. Desorption can be done automatically after each load, or it can be done at the end of the day. If not performed regularly, the carbon bed will become saturated and be ineffective for PERC recovery. The adsorption system can handle high volumes of air, having relatively low solvent concentrations while maintaining a high PERC removal efficiency, but frequent desorbing is needed and steam regeneration produces contaminated waste water.
Refrigerated condensers cool solvent-laden air below the dew point of the vapour to recover PERC, and operate on the principle that the ability of air to hold a solvent in the vapour state varies with temperature. Refrigerated condensers are used in approximately 65% of controlled machines. The process can achieve 95% vapour control in dry-to-dry machines and 85% control in transfer machines. Condensers require little maintenance and minimize the potential for waste water because steam regeneration is not required. They do require higher solvent concentrations than a carbon adsorber. Water vapour may pose a problem because it can condense and freeze, impeding gas flow and heat transfer (EPA 1991b).
Solvent alternatives to PERC
Alternative dry-cleaning solvents have been substituted for PERC. Flammable, petroleum-based solvents generally have higher exposure limits than PERC. These petroleum-based solvents are less aggressive at removing soils than PERC. Because their vapour pressures are lower than PERC, exposures from inhalation will generally be lower. However, adverse health effects are possible, including asphyxiation, central nervous system depression and skin and mucous membrane irritation. Contamination of aliphatic hydrocarbons with benzene will significantly increase the hazard.
Two different approaches have been taken in Germany to reduce the fire hazard posed by petroleum-based solvents: developing safer solvents and redesigning machines.
Recently developed petroleum-based solvents, widely used in Germany, are either straight-chain, branched or cyclic paraffins with a chain length of between 10 and 12 carbons. These petroleum-based solvents have an atmospheric lifetime of only a few days, are halogen-free, do not lead to ozone depletion and play only a minor role in the greenhouse effect. Some of the German requirements for petroleum-based, dry-cleaning solvents are outlined below (Hohenstein Institute 1995):
- Boiling range between 180° and 210ºC
- Aromatic, benzene, halogen and polycyclic aromatic content less than 0.01 wt%
- Flashpoint higher than 55ºC
- Thermally stable at operating conditions.
Dry-cleaning machines manufactured for petroleum-based solvents in Germany today are much safer than those of the past. Because petroleum-based solvents are combustible, additional safety measures are required on machines using them. Technical advances improve machine safety and greatly reduce the risk of fire/explosion. The following measures can be taken in combination or separately:
- Using an inert gas, such as nitrogen or argon, to displace oxygen in the drum and ensure that oxygen concentration is sufficiently low (approximately 4%) to prevent combustion
- Operating under a vacuum to remove oxygen and lower its concentration to below 4%
- Ensuring that the lower explosive limit (LEL) is not exceeded, or if the LEL is not known, ensuring that operating temperature remains 15ºC below the flashpoint
- Ensuring that vapour concentration remains below 50º of the LEL, by controlling operating temperatures or by providing sufficiently high airflow.
Wet cleaning is a developing technology, distinct from traditional laundering in that it is a more gentle process and can be used on many fabrics that were formerly dry cleaned. Four factors play an essential role in soil removal: temperature, time, mechanical action and chemical agents. Only the proper blend of these factors achieves the best cleaning results (Vasquez 1995). There are minor variations of machine wet cleaning, but all techniques use:
- Specially formulated wet-cleaning soaps and spotting agents
- Increased extraction of water prior to drying (extraction speeds as high as approximately 1,000 revolutions per minute)
- Close monitoring of heat and moisture content during the drying process
- Machines having less mechanical action during washing, accomplished by speed reduction and time limits.
Garments are washed with various levels of limited mechanical action, based on garment type and amount of soilage. The greatest risk occurs during drying. Many fibres can be fully dried with little or no difficulty. However, delicate garments or garments susceptible to shrinkage must be dried for only a few minutes before being hung to air dry. Because of these problems, most wet-cleaned garments require more finishing work than solvent-cleaned garments. Long drying times and more finishing work substantially increase processing time (Earnest and Spencer 1996).
Today, wet cleaning use is limited because the technology does not yet completely eliminate the need for solvents. It has been estimated that wet cleaning can safely clean approximately 30 to 70% of garments traditionally cleaned in solvent (Rice and Weinberg 1994). There are still problems with fibre damage, bleeding of dyes and, most importantly, cleaning ability. Inappropriate use of wet cleaning can expose shop owners to liability for damaged clothing. For this reason wet-cleaning advocates are working to persuade garment manufacturers to use fabrics that can be more easily wet cleaned.
Hazards in Laundries and Dry Cleaning Facilities
In the workplace PERC can enter the human body through both respiratory and dermal exposure (ATSDR 1995). Symptoms associated with respiratory exposure include depression of the central nervous system; damage to the liver and kidneys (RSC 1986); impaired memory; confusion; dizziness; headache; drowsiness; and eye, nose and throat irritation. Repeated dermal exposure may result in dry, scaly and fissured dermatitis (NIOSH 1977).
US National Cancer Institute and National Toxicology Program studies have established a link between PERC exposure and cancer in animals. Human studies show an elevated risk of urinary tract (Duh and Asal 1984; Blair et al. 1990b; Katz and Jowett 1981), oesophageal (Duh and Asal 1984; Ruder, Ward and Brown 1994) and pancreatic cancer (Lin and Kessler 1981) among dry-cleaning workers. The International Agency for Research on Cancer (IARC) recently classified PERC in group 2A (probably carcinogenic to humans) and dry cleaning in group 2B (possibly carcinogenic to humans) (IARC 1995b). The Environmental Protection Agency (EPA) regulates PERC as a hazardous air pollutant.
US Occupational Safety and Health Administration (OSHA) data include numerous personal samples in dry-cleaning shops over the permissible exposure limit (PEL) of 100 ppm, 8-hour time-weighted average (TWA) (OSHA 1993). The machine operator is typically exposed to the greatest concentrations of PERC. US National Institute for Occupational Safety and Health (NIOSH) studies have shown that in many dry-cleaning shops having traditional machines, extremely high operator exposures occur during loading and unloading. Because loading/unloading occurs frequently throughout the day, in many instances exposure during this activity can account for 50 to 75% of the operator’s TWA exposure (Earnest 1996). Occupational exposures can be reduced by using modern dry-cleaning machines, solvent substitution, isolation of the process and effective local and general ventilation near the dry-cleaning machines.
Exposure to chemicals other than PERC
A wide variety of chemicals is present in laundries and dry-cleaning establishments. There is potential exposure through skin or eye contact or inhalation of vapours. Skin damage may occur from chronic or acute exposure. Chemicals that readily vaporize and have a high toxicity may pose a risk from inhalation, although this is generally considered to be of less concern than injury to the eyes or skin. The chemicals commonly used in the United States to treat stains through spotting are trichloroethylene; ketones, especially methyl isobutyl ketone (MIBK); petroleum naphtha; and hydrofluoric acid. Oxidizers, such as chlorine bleaches, may pose a hazard if used in the presence of many common compounds, such as turpentine, ammonia or fuel gases. Detergents containing enzymes may cause immune reactions in many workers. The combined exposures of the dry-cleaning solvent, PERC and various other chemicals is also a concern.
Ergonomic risk factors
Ergonomic hazards in the cleaning industry primarily occur among pressers. Pressing is a dynamic and repetitive task requiring reaching, precision gripping and awkward postures. Ergonomic risk factors are also present during material handling when heavy lifting may occur, especially in commercial laundries.
The dry-cleaning industry has traditionally had a problem with fires. Part of the reason for this problem has been the widespread use of flammable and combustible liquids as a cleaning medium. The flammability of petroleum-based solvents continues to present an acute health and safety hazard. Approximately 10% of dry-cleaning shops in the United States use traditional, petroleum-based solvents, such as Stoddard solvent or mineral spirits. Even dry-cleaning shops that use non-flammable PERC face important fire hazards. If heated sufficiently, PERC will decompose into hydrogen chloride and phosgene gases. The production of hydrogen cyanide or carbon monoxide is another cause for concern during a fire. Hydrogen cyanide is produced when materials that contain nitrogen, such as many natural and synthetic fibres burn. Carbon monoxide is formed during incomplete combustion. All dry-cleaning shops have a large number of potential fuels and ignition sources.
Dry-cleaning machine designers must avoid conditions that can lead to a fire to occur and must ensure that their machines operate safely. Likewise, shop owners must take appropriate steps to prevent hazardous conditions from developing. Some common causes of fires in all businesses are electrical malfunctions, friction, open flames, sparks, static electricity, hot surfaces and smoking (NIOSH 1975).
Cleaning facilities have several possible sources of severe burns. In the pressing station, burns may result from contact with the head of a press, lines transporting steam, or the steam itself. Insulation of pipes and surfaces, and use of various guarding techniques, can help prevent burns.
Although modern boilers are of safer design than earlier models, they are still used to produce large quantities of steam and must be operated safely. Many of the needed precautions can be found in the US National Fire Protection Association’s Code 32, Standard for Dry Cleaning Plants, and its Fire Protection Handbook (NFPA 1991). Recommendations in these documents include building code requirements, proper storage and isolation of flammables, fire extinguishers and sprinkler systems. Recommendations concerning the build-up of gases around the boiler address ways to eliminate gas leakage and ensure proper ventilation.
Mechanical hazards are always a concern when powered equipment is used. Presses pose a significant mechanical hazard. Presses designed to be activated by only one hand leave a potential for the worker’s free hand to be caught between the presses. Belts, drive chains, shafts and couplings should be guarded to prevent accidental contact. All moving components of machines should be guarded to prevent body parts from becoming caught in a pinch, nip or shear point. The most common methods of guarding a hazard are enclosing the operation, interlocking devices, moving barriers, removal devices, remote controls, two-hand tripping devices and electronic safety devices.
Numerous measures can be taken to limit electrical hazards. Especially important is proper insulation and grounding. Identification and guarding of live parts also helps to prevent injury from electrical current. Electrical hazards can be compounded by the presence of moisture. Ground-fault circuit interrupters are designed to shut off power if high current passes through an unintended path. When selecting electrical equipment, the recommendations of established codes and standards, such as the US National Fire Protection Association 70, the National Electrical Code and the American National Standards Institute’s C2, should be followed. Guidelines for appropriate use of electrical equipment are given elsewhere in this Encyclopaedia.
Heat stress can afflict workers who must labour for extended periods of time in the hot environments that exist in many cleaning facilities. Heat stress may be compounded in the summer months, particularly if the shop is not air conditioned (air conditioning is not common in this industry). Both physical and environmental factors will modify the effects of heat. Acclimatization, body surface area to weight ratio, age and diseases, water and salt balance and physical fitness all play a role in the likelihood an individual will be affected by heat stress.
Slips, trips and falls
The hazard of slips, trips and falls are especially pertinent to cleaning facilities, which are often crowded with people and equipment. Without clearly established aisles and with a large number of containers holding solvents or water, spills can easily occur, resulting in a slippery floor. To control this hazard, regular housekeeping must be emphasized, facility layout must be carefully planned, and floor surfaces should be of non-slip materials. The workplace should be maintained in a clean, orderly, sanitary condition, and any spills should be cleaned up promptly.
Laundering hospital linens puts sorters at risk from overlooked sharp objects in sheets or uniform pockets. Both dry cleaners and launderers may encounter freshly soiled garments that have been contaminated with human body fluids. Garments that have come from dental and medical offices or labs, blood banks, drug treatment centers, clinics, mortuaries, ambulances and other health-care facilities can be reasonably suspected to contain potentially infectious materials. In many countries, shops that handle garments from these sources must comply with the occupational standards governing exposures, such as the OSHA regulations governing bloodborne pathogens.
Environmental and Public Health Concerns
Environmental and public health concerns have resulted in dramatic changes in environmental regulations affecting the dry-cleaning industry in recent years. Adjacent apartments and businesses can be exposed to PERC vapours by diffusion through walls or ceilings; indoor airflow through holes in ceilings, pipe chases or vents; and through PERC emissions vented outside of the shop that are re-entrained through opened windows or ventilation units. Groundwater or soil contamination can occur through frequent or large solvent spills that might occur during transfer of solvent from a delivery truck to the dry-cleaning machine. Soil contamination might also occur through improper disposal of separator water into the sanitary sewer. Finally, consumers may be exposed from PERC residuals in poorly dried garments. This is of particular concern if the cleaning machine is not functioning properly or the dry cycle is shortened to improve productivity.
Acknowledgement: This article is largely based on materials assembled and published by the US National Institute for Occupational Safety and Health (NIOSH).