Parts Washing Technologies

November 1999 - TI#20835
Air Force Cleaning Requirements
Parts Washing Technologies
Immersion Tanks
Vapor Degreasers
Spray Cabinets
Bioremediating Parts Washers
Cleaning Solutions
Solvent Cleaners
Aqueous Cleaners
For More Information
Document References
P-D-680: Friend or Foe?

Solvent products have traditionally been used for removing dirt, greases, and oils in parts cleaning operations because they work well and dry quickly. Unfortunately, many of these products are hazardous materials and become hazardous waste when they are no longer suitable for cleaning. Decades of using these products has caused extensive environmental contamination requiring costly soil and ground water remediation. One approach to limiting environmental hazards and controlling disposal costs has been to implement the use of "environmentally preferable" cleaning products and processes. Unlike solvent cleaners, many of these water-based (aqueous) and semi-aqueous products are initially non-hazardous to the environment and are generally less hazardous to store and use.

Although "environmentally preferable" products have had a significant positive impact on industry and the environment, they are not without potential problems of their own. Some of these cleaners may have a reduced cleaning ability when compared to traditional solvent cleaners, and there is also considerable concern that aqueous cleaners, because of their water content and longer drying times, may lead to corrosion of some metal parts. Additionally, individual aqueous and semi-aqueous cleaners do not appear to work on as wide a variety of materials or contaminants as solvent cleaners do, thus requiring facilities to stock several specialized cleaning agents instead of just one or two general purpose solvents. Finally, contaminants from parts being cleaned can concentrate in the cleaning solution turning these otherwise non-hazardous products into a hazardous waste; thus minimizing any potential disposal cost savings.

Each year, the Air Force spends substantial sums of money maintaining its various weapon systems. A large component of these expenditures involves the purchase, use, and disposal of various solutions used to clean and maintain critical aircraft and other weapon systems components. Like industry, the Air Force has, in the past, relied heavily on the use of solvent products for its parts cleaning needs. It has also embraced the transition to "environmentally preferable" cleaning products and processes and, again like industry, has had mixed although mostly positive results.

With the benefit of nearly a decade of experience in reducing reliance on hazardous materials (HAZMATs), the Air Force's policy on HAZMAT reduction has evolved away from initial efforts that focused on specific chemical lists to the current "risk and compliance-based" approach of the Hazardous Materials Reduction Prioritization Process (HMRPP). This change in the approach to managing HAZMATs, along with substantial growth in the technology of solvent chemistries and cleaning equipment, has led many pollution prevention managers, and those who repair and maintain Air Force weapon systems, to take a second look at the products and processes used to clean equipment parts. The purpose of this fact sheet is to provide an overview of common parts washing technologies and systems with the goal of assisting Air Force personnel in making informed decisions relative to their parts cleaning needs. It highlights general types of parts washers, their capabilities and intended uses, and also includes a discussion of the different classes of cleaning solutions, their benefits, and associated hazards. Finally, the fact sheet examines the benefits, hazards, and uses of P-D-680, a common petroleum solvent still used in Air Force cleaning operations.

Air Force Cleaning Requirements
Repairing and maintaining the vast array of weapon systems, vehicles, and support equipment contained in the Air Force inventory requires the removal of various contaminants (dirt, oils, and greases) from metal and plastic components. Weapon system component cleaning operations are typically governed by Air Force Technical Orders (T.O.s) in order to meet crucial performance requirements. The T.O.s mandate which parts must be cleaned, how clean they must be, and what processes, chemicals, materials, and procedures may be used to clean them.

Deviations in selecting cleaning compounds and/or processes from what is specified in the T.O. is not allowed and must never be done unless prior approval is granted from the T.O. Manager via a "T.O. charge."

Cleaning requirements in a T.O. will often reference cleaning compounds directly or through a governing military specification (MILSPEC) or federal specifi-cation (FEDSPEC). These specifications provide detailed information on the composition and performance requirements of the cleaning compound. When a cleaning process in a T.O. references a MILSPEC or FEDSPEC, only products conforming to the requirements of the specification may be used. For example, MILSPEC MIL-C-29602 provides requirements for cleaning compounds that must be used in certain parts washers and spray cabinets. Requesting the information from product manufacturers, searching databases such as the Hazardous Material Information System (HMIS), or consulting the Qualified Products List (QPL) for the specification may be used to identify conforming products. Additionally, PRO-ACT, with the assistance of the T.O. Manager can assist in identifying products that conform to a particular specification.

T.O. Managers are increasingly incorporating references and authorization to use environmentally preferable cleaning compounds and technologies into their maintenance instructions; however, many still require the use of solvent cleaners. Under the HMRPP, inputs are received from the weapon system user community and are used to assist T.O. and Air Force Single Managers in prioritizing and selecting substitute products/materials for the hazardous materials currently mandated in their MILSPECs and T.O.s. Their approach to selecting which products and methods to use for cleaning weapon system components is very rigorous, and is based on performance needs, cost, and the overall risk associated with the process. Risk is evaluated for all phases of the cleaning process including procurement, storage, use, and disposal of the cleaning product, and is examined in terms of impact on the health of the workers and the environment, and the potential for non-compliance with applicable laws and regulations. "Environmentally preferable" cleaning products are generally thought to be less risky than traditional solvent-based cleaners. However, with recent advances in solvent technology and the development of "designer" solvents (discussed below), this is not always true. When cost and performance factors are also taken into consideration, "environmentally preferable" products and methods may not always be the best choice.

In areas where cleaning activities are not mandated by T.O. requirements, installations may select both the cleaning product and the method used in the maintenance process. The same approach used by weapon system personnel--evaluating performance needs, costs, and overall risk--should be used by installation-level personnel in selecting cleaning products and methods for processes under their control. Readers that are contemplating a review of their cleaning operations should review the "Evaluating and Selecting Potential Alternatives" section of PRO-ACT's November 1998 "Product Substitution" Fact Sheet. This section presents a step-by-step approach for choosing alternatives that is based on the protocols used by PRO-ACT in responding to product substitution inquiries.

Air Force weapon system, vehicle, and equipment parts are cleaned for a variety of reasons. As discussed in the Product Substitution Fact Sheet, understanding how the current product is used is crucial in selecting a suitable alternative product. Thus, in addition to the many factors already listed in the Product Substitution Fact Sheet, knowing what type of cleaning is being performed is an important factor in deciding what types of cleaners and methods should be considered. General cleaning categories include:

  • Pre-cleaning - non-precise cleaning operation designed to remove gross contamination from a component prior to initiating a follow-on cleaning process.
  • Cosmetic cleaning - cleaning to facilitate maintenance procedures and/or make the component look aesthetically pleasing.
  • Pre-paint cleaning - cleaning prior to the application of a paint or primer to improve coating adhesion.
  • Pre-plate cleaning - cleaning prior to initiating plating, welding, anodizing or other surface finish operation to aid adhesion of the surface finish.
  • Pre-bond cleaning - cleaning component surfaces prior to application of adhesives or sealants to ensure proper adhesion of the cleaned surfaces.
  • Pre-non destructive inspection (NDI) cleaning - cleaning which occurs prior to critical NDI operations such as fluorescent dye penetrant inspections.
A second important factor in determining how the current product is being used is knowing what contaminants are being removed by the cleaning process. For example, are the contaminants oils and greases, soil particles, etc., or combinations of these? Also, how are the contaminants affixed to the part - are they held on by a chemical attraction or are they "baked on" like carbon deposits on an engine nozzle?

The next step in evaluating and selecting a substitute cleaning product and/or method is identifying potential alternatives. There are at least a dozen different types of cleaning technologies and hundreds of different commercial cleaning products that are available for use by Air Force personnel. The discussions that follow on parts washing technologies and cleaning solutions are not all inclusive, but rather reflect those that are most commonly available and would be considered sufficient for 95% of Air Force cleaning needs.

Parts Washing Technologies
As mentioned above, there are at least a dozen commercially available technologies that can be used for cleaning Air Force weapon system, vehicle, and equipment parts. These technologies range from new and exotic technologies such as plasma and laser cleaning, to more conventional methods like immersion tanks and vapor degreasers. This fact sheet focuses on four conventional technologies that are currently employed at Air Force installations around the world. Additional information on these technologies, as well as others, can either be found in the references listed in the back of the fact sheet or obtained from PRO-ACT.

Immersion Tanks
One of the most common parts washing technologies is the immersion or soak tank. This system typically consists of a chest-type cabinet with a lid that is filled with cleaning solution. Depending on the type of cleaning solution used, the tank may also have a heating system to warm the solution. Parts are placed into the tank either directly or in baskets, and are allowed to soak for a specified amount of time. Often times the maintenance technician will use a brush or spray wand to facilitate removal of the contaminant(s). Several variations on the standard immersion tank system have been developed to impart mechanical agitation into the cleaning process. These variations include the use of:

  • Spray nozzles in the tank walls that create turbulence within the cleaning solution;
  • Oscillators that move the parts back and forth through the cleaning solution;
  • Ultrasonic units that use sound waves to vibrate the part; and
  • Combinations of the above devices.
Immersion tanks are relatively inexpensive and typically require very little labor to operate since the parts are often left on their own to soak. However, there can be substantial costs associated with the disposal of spent cleaning solutions, particularly if a solvent is used. One way to reduce this cost is to extend the solvent's usability by separating it from the contaminants in a filtration or distillation system. Also, the addition of one or more mechanical agitation devices eases the need of the system to solely rely on the cleaning solution to remove the contaminant(s) from the parts. Thus, it may be possible to use a less aggressive aqueous or semi-aqueous chemical cleaner. Although, as noted above, these products may also present a disposal problem due to collection of hazardous contaminants, there are services available that will collect and recycle the solutions on a regular schedule for a standard fee. Finally, although immersion tanks are typically used for pre-cleaning and cosmetic cleaning purposes, using one or more of the devices listed above, along with an appropriate cleaning agent, may allow the system to be used for more demanding cleaning needs.

Vapor Degreasers
Vapor degreasing systems have typically been used when it is necessary to achieve a high level of cleanliness, particularly when the parts being cleaned have unusual or complex shapes such as small crevices and/or blind holes. The system typically consists of a chest-type cabinet with a lid that is partially filled with a solvent-based cleaning solution. There is a heater in the bottom of the tank that heats the solvent to its boiling point, which generates vapors. The vapors then fill the tank to a level established by the placement of condensing coils around the tank's perimeter. These coils create a cold layer of air that serves to trap the vapors and prevent them from escaping into the atmosphere. When the part, at room temperature, is placed into the heated vapor zone inside the tank, the vapors condense onto the part. The solvent then dissolves the contaminant(s), drips back down into the bottom of the tank along with the contaminant(s), and is then revaporized. Because the cleaning action of a vapor degreasing system is dependent on a temperature differential between the vapor and the part, the efficiency of the process decreases as the part becomes warmer. For this reason, some systems are equipped with a wand that can be used to spray warm solvent onto the part to complete the cleaning process. Other systems may have a warm liquid compartment where the part(s) may be dipped.

The most troublesome aspects of using a vapor degreasing system can be disposing of the spent solvent and controlling solvent vapors. However, as noted above, filtration and distillation systems can greatly extend the usability of a solvent and reduce associated disposal costs. Also, many of the newer vapor degreasers use a completely closed loop system for generating the vapors, cleaning the parts, and recondensing the vapors. These vacuum degreasers can virtually eliminate vapor releases to the atmosphere and have allowed many in industry to continue to use more traditional halogenated solvents, such as methylene chloride and 1,1,2-trichloroethylene (discussed below), for certain parts cleaning applications without exceeding very strict emission discharge regulations. Recent advances in solvent technologies have also helped reduce some of the negative impacts of using vapor degreasers. The newer "designer" solvents such as the HFEs, HFCs, PFCs, and nBP (also discussed below), work well in vapor degreasing systems and have more favorable toxicological and environmental profiles than more traditional chlorinated solvents.

Another variation of vapor degreasers is the cosolvent system that uses two liquids; one for cleaning the part and another that acts as a drying agent. The U.S. Navy recently evaluated an Isopropyl Alcohol/Cyclohexane cosolvent vapor degreaser for cleaning precision instrument bearings at two of their Naval Air Stations with very favorable results (copies of the report are available from PRO-ACT).

Spray Cabinets
Spray cabinets can generally be thought of as industrial cousins of the home dishwasher. Dirty parts are generally loaded into baskets and then placed into the cabinet. Heated water mixed with an aqueous cleaning solution (typically 140oF to 200oF) is then sprayed onto the parts for a specified amount of time. Some models come with a turntable that rotates the parts through the spray. Other models come with a fixed base and rotating sprayers, while still others have rotating turntables and sprayers. Often the spray nozzles can also be adjusted.

Spray cabinets are completely closed loop systems. They can be programmed to apply wash, rinse, and even heated air drying cycles and then left alone. This saves labor in comparison to immersion tanks where the parts have to be scrubbed by hand. Wash and rinse water can be recycled through the use of filters to remove particulate matter and, in some models, oil skimmers built into the machine. Because of potential material incompatibility issues, many spray cabinet manufacturers require users to use only certain cleaning solutions. Failure to do so may invalidate the manufacturer's equipment warranty. For additional information on aqueous parts washers, including the disposal of wastewater, see the section below on aqueous cleaning solutions.

Bioremediating Parts Washers
The latest technology entry into the parts washing market is the bioremediating parts washer. These systems use a warmed, aqueous-based degreasing fluid containing emulsifiers and surfactants that is sprayed on to the part in a self-contained sink. The fluid removes contaminants from the part and drains into a reservoir or filter where naturally occurring, aerobic, non-pathogenic microbes break down the oils and greases into carbon dioxide, water, and other harmless by-products. Manufacturers of these products claim that the degreasing fluid can be used continuously with only periodic "top offs" needed to replenish losses due to evaporation. They also claim that the filters are non-hazardous and can be discarded into a municipal solid waste landfill. (Note: PRO-ACT recommends that users of bioremediating parts washers properly characterize the filter waste stream prior to disposal to ensure they do not become contaminated with metals or other hazardous contaminants.)

One of the bioremediating parts washers was tested in Air Force vehicle maintenance operations under the Air Force Materiel Command's Management & Equipment Evaluation Program (MEEP). The results of the test indicated that the parts washer performed very well in cleaning a variety of vehicle and machinery parts. The report also concluded that this technology has the potential to save installations money when comparing its costs to those associated with purchasing, using, and disposing of petroleum-based solvents. This report is also available from PRO-ACT.

Cleaning Solutions

Solvent Cleaners
Solvent cleaners are derived from the distillation and refinement of crude oil. They operate primarily on the principle that "like dissolves like;" therefore they tend to work best for removing organic materials from parts such as oils and greases. This dissolving action means that some solvents may be incompatible with certain types of plastics (which are also derived from oil) found in parts washing equipment. Most products in this class of cleaners contain aliphatic hydrocarbons (straight carbon chain structures) that have had one or more of their hydrogen atoms replaced with other "components." Examples of aliphatic hydrocarbon cleaners are methylene chloride and methyl ethyl ketone (MEK). Other solvent cleaners contain aromatic hydrocarbons (ringed carbon structures), again with one or more of their hydrogen atoms replaced with other "components." Examples of aromatic hydrocarbon cleaners include toluene and xylene. A third group of solvent cleaners is the petroleum distillates that contain a mixture of aliphatic and aromatic hydrocarbons. Examples of these cleaners are white spirits and P-D-680. Additional details on the properties and uses of each of these general classes of solvent cleaners are presented below (information of petroleum distillates is contained in the special section on P-D-680).

Aliphatic Hydrocarbon Solvent Cleaners:
The properties of these cleaners are based in large part on what "components" are used to displace hydrogen from the carbon atoms. Thus, most of these products can be further divided into the following groups:

  • Halogenated Compounds: These products contain one or more halogens (chlorine, fluorine, and bromine being the most common) attached to the carbon structure. The physical properties of these cleaners can vary greatly depending on which halogens are used, how many are used, and what carbon atom(s) they are attached to. Classes of Halogenated compounds include:
  • Chlorofluorocarbons (CFCs) - these cleaners are classified as Class I Ozone Depleting Substances (ODSs) and were banned from production in the United States at the end of 1995. They are highly volatile (they evaporate quickly), nonflammable, and generally nontoxic. The use of these products in the Air Force is prohibited except for certain T.O. directed applications.
  • Hydrochlorofluorocarbons (HCFCs) - these products are classified as Class II ODSs and are targeted for elimination under international agreements. The formulation that has been used most extensively for parts cleaning is HCFC-225 which is considered toxic.
  • Hydrofluorocarbons (HFCs) - these products are considered mild solvents that are usually mixed with additives to enhance their cleaning power. They have a low volatility (in comparison to CFCs and HCFCs) do not deplete atmospheric ozone, and do not contribute to global warming. HFCs are also considered relatively nontoxic and are compatible with most materials.
  • Perfluorocarbons (PFCs) - these cleaners are considered weak solvents and must be mixed with additives to enhance their cleaning abilities. They are nontoxic, nonflammable, compatible with most materials, and do not deplete atmospheric ozone. Conversely, they are very stable structures, and thus have a significant global warming potential.
  • n-Propyl Bromides (nPBs) - this formulation is very closely related to 1,1,1-trichloroethane in terms of its physical characteristics and cleaning power. Its ozone depleting potential is similar to that of HCFC-225, yet nPBs are not classified as a Class I or II ODS. A stabilizer compound must be added to prevent the formation of hydrobromic acid when it comes in contact with water. nPBs are considered to be relatively nontoxic. They have not yet been approved by the EPA under the Significant New Alternative Program (SNAP).
  • Hydrofluoroethers (HFEs) - these cleaners are nontoxic, compatible with most materials, do not deplete atmospheric ozone, and do not contribute to global warming. They, like PFCs, are generally weak cleaners and must be mixed with additives to enhance their cleaning ability.
  • Miscellaneous Compounds - this group includes cleaners such as methylene chloride, carbon tetrachloride, 1,1,1-trichloroethane, perchloroethylene, and 1,1,2-trichloroethylene. Although the physical properties, health effects, and environmental fate of these cleaners can vary greatly, they are all listed as hazardous wastes upon disposal in accordance with Title 40 Code of Federal Regulations (CFR) 261.31. Some of these products (carbon tetrachloride and 1,1,1-trichloroethane) are Class I ODSs and their use in the Air Force is restricted.
  • Alcohols: Alcohols are characterized by the presence of an oxygen/hydrogen group attached to the carbon chain. The most common alcohol used in industrial cleaning operations is isopropyl alcohol (IPA). It is flammable and highly volatile; a characteristic that makes it extremely useful as a rinsing/drying agent in cosolvent applications. This also makes waste IPA a characteristic hazardous waste upon disposal in accordance with Title 40 CFR 261.261.21. IPA is considered nontoxic and does not deplete atmospheric ozone. It is also compatible with most materials.
  • Ketones: Ketones are a class of chemicals that have a hydrogen atom along the carbon chain replaced by an oxygen atom. Common ketones used for parts washing include methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and acetone. MEK and MIBK are both considered mildly toxic and neither is listed as a carcinogen. They are also both considered volatile and flammable which makes them a characteristic hazardous waste upon disposal in accordance with Title 40 CFR 261.21. In addition, MEK is listed as an EPA 17-priority pollutant and, if threshold concentration quantities are reached, can cause a wastestream to be classified as a toxic hazardous waste upon disposal.
  • Aromatic Hydrocarbon Solvent Cleaners: This class of cleaners have excellent cleaning properties and includes, among others, benzene, toluene, and xylene. In general, all of these cleaners are flammable and highly volatile. They are also considered harmful if inhaled or absorbed through the skin, and are also known to be carcinogenic. These cleaners are heavily regulated under various air and water programs, and must also be disposed of as a hazardous waste in accordance with Title 40 CFR Subpart D, "Lists of Hazardous Wastes."

Aqueous Cleaners
Water-based (aqueous) cleaning products work through water's ability to solubilize and/or suspend contaminants in solution. To aid solubilization/suspension, and to assist with the overall cleaning process, many aqueous cleaners will also contain one or more of the following additives:

  • Surfactants - which allow the water to emulsify or trap organic contaminants.
  • Builders - which provide a pH buffer capacity to acidic and alkaline cleaners to lengthen their useful "lifespan."
  • Chelators - which serve to "bind up" free metal ions in the cleaning solution to prevent them from interacting with the part being cleaned.
  • Dispersants - which prevent removed contaminants from re-adhering to the cleaned part.
  • Defoamers - which prevent problems in the cleaning process due to excessive foaming.
Aqueous cleaners are typically used at concentrations of 0.5 to 5% of the active ingredients, whereas solvent cleaners are used at full strength. Most aqueous cleaners require some type of agitation to enhance the overall cleaning process, and a drying step typically needs to be added in order to minimize rusting of metal parts. In general, aqueous cleaners can be divided into three groups depending on their pH. These groups include:

Acidic Aqueous Cleaners: These cleaners have a pH in the range of less than or equal to 6. Water is usually mixed with an appropriate amount of an acid (chromic acid, nitric acid, sulfuric acid, etc.) and builders to achieve, and maintain, the desired pH level. Acidic cleaners tend to work well in pre-plate, pre-bond, and pre-paint cleaning processes, however, they are generally not recommended as general degreasing agents due to their aggressive action against parts washing system components.

Neutral Aqueous Cleaners: Neutral cleaners operate over a pH range of 6 to 8. The addition of surfactants, corrosion inhibitors, and dispersants, along with mechanical agitation, make this class of cleaners particularly well suited for removing organic (greases and oils) and inorganic (dirt and grime) contaminants.

Alkaline Aqueous Cleaners: These cleaners operate at pHs in excess of 8; although, a range of 8 to 13 is most common for removing soils, oils, and greases. Many different alkaline agents, such as carbonates and hydroxides, can be added to water to create these agents. The use of phosphates, once a common cleaning additive, has been reduced because of its tendency to disrupt aquatic ecosystems. Alkaline cleaners are also very good at removing oils and greases which tend to be naturally acidic.

In selecting an aqueous cleaning system (cleaning agent and washer), it is important to consider the type of contaminant(s) that need to be removed and the type of material being cleaned. Once these selections have been made, other parameters, such as operating times, the concentration of the cleaning agent, and the temperature at which the system operates, will all have to be evaluated and optimized. Once this is done, users can usually expect very good results.

The drive behind using aqueous cleaners is that they are thought to be less hazardous to workers and more "environmentally friendly" than solvent-based cleaners. Aqueous cleaners typically release very few, if any, volatile organic compounds (VOCs). Most are also considered "biodegradable," meaning that they are broken down in the environment into benign substances. However, just because an aqueous cleaner is "environmentally friendly" going into the cleaning process does not mean it will exit that way. Aqueous cleaning processes generate wastewater that must be properly characterized and disposed of. Two studies, one accomplished by the U.S. Army's Construction Engineering Research Lab and the other by the Iowa Waste Reduction Center, found a wide range of contaminant concentrations in wastewater from aqueous parts washers. Some contaminant types and levels were such that a minimal amount of pretreatment was all that was necessary prior to discharging the wastewater into the sanitary sewer system. Other types and levels required that the wastewater be containerized and disposed of as a hazardous waste.

Whenever possible, "environmentally preferable" solutions and processes should be used to clean Air Force weapon system, vehicle, and equipment parts. In general, these products present a decreased risk to worker health and the environment. However, they are not appropriate for all situations. Therefore, pollution prevention managers and maintenance technicians should avoid the wholesale dismissal of solvent cleaning products and the technologies that use them. Changes in chemical formulations and equipment over the past decade have minimized many of the concerns that once plagued these products. Selecting an appropriate part washing technology is a decision that should be based on a careful analysis of performance needs, cost, and the overall risk of the process to worker health and the environment.
For More Information...
Integrated Solvent Substitution Data System (ISSDS): This system, developed by the Environmental Protection Agency (EPA), uses a variety of information sources and databases to assist users in selecting alternative cleaning solutions and processes that best suit defined operating and material requirements. The interactive ISSDS program can be accessed through EPA's World Wide Web (WWW) site at

The Air Force Corrosion Prevention and Control Office: The AF Corrosion Office, a subdivision of the Air Force Research Laboratory, is located at Robins AFB, GA and is tasked with ensuring the AF has a viable program to prevent, detect, and control corrosion and to minimize its impact on AF systems. The office conducts/facilitates research on many aspects of maintaining the Air Force's weapon systems and is currently investigating the use of aqueous parts washers throughout the service. Their WWW site at is an excellent source of information and publications related to painting, depainting, and cleaning weapon systems and their components.

U.S. Army Solvent Substitution Program: The Army's Acquisition Pollution Prevention and Support Office, in conjunction with their Center for Technical Exchange for Solvent Substitution, have developed the "Standard Protocol for Selecting General Cleaning Agents and Process." This protocol is designed to assist managers in selecting the best cleaning agent and process for a specific operation. Copies of the protocol, which is being developed as an American Society for Testing and Materials (ASTM) guide, are available from PRO-ACT or on the WWW at

Precision Cleaning World Wide Web Site: This site, sponsored by "Precision Cleaning" magazine, offers information on a wide variety of cleaning issues. A search engine allows users to view previous magazine issues, obtain cleaning-related compliance information, and preview the latest in cleaning technologies. The WWW site address is

PRO-ACT: PRO-ACT has an extensive database of practical solutions to parts cleaning needs. We can assist with determining requirements for using particular types of cleaners/technologies, as well as whether or not T.O. Managers have authorized alternative products. Contact PRO-ACT at DSN 240-4214 or e-mail us at

Document References
  1. "U.S. Army Solvent Substitution Program,"
  2. "Solvent Alternatives Guide (SAGE),"
  3. "Transportation Pollution Prevention Model Shop Report," HQ AFCEE/EQ, July 1998.
  4. "Preproduction Initiative-NELP Aqueous Parts Washer (Large) Final Report," NAS Mayport, FL and NAS North Island, CA.
  5. "Preproduction Initiative-NELP Isopropyl Alcohol/Cyclohexane Vapor Degreaser Final Report," NAS North Island, CA.
  6. "Cleaning Compounds for Parts Washers and Spray Cabinets," MIL-C-29602, 28 February 1995.
  7. "Parts Washing Alternatives Study - United States Coast Guard. Project Summary and Report," Lockheed Environmental Systems and Technologies Co. and EPA, January 1995.
  8. "Evaluation of Automatic Aqueous Parts Washers," Construction Engineering Research Laboratory (CERL), US Army, December 1997.
  9. "Stoddard Solvent," ToxFAQs, Agency for Toxic Substances and Disease Registry (ATSDR),
  10. "Toxicological Profile for Stoddard Solvent," US Department of Health & Human Services, June 1995.
  11. "P-D-680 in Army Aviation Maintenance," Hazardous Technical Information Services (HTIS) Bulletin, Jul-Aug 1998.
  12. "P-D-680 Alternatives Point of Contact," CrossTalk Edition 31, PRO-ACT, December 1996.
  13. "Federal Specification - Dry Cleaning and Degreasing Solvent," P-D-680, 16 May 1995.
  14. Title 40 CFR Subparts C and D.
  15. "Organic Solvent Cleaning Systems," Parts Cleaning Web,
  16. "Aqueous Cleaning Systems," Parts Cleaning Web,
  17. "Chemistry for Environmental Engineering," 4th Edition, Editors: Sawyer, C. N., McCarty, P. L., and Parkin, G.F., McGraw-Hill, Inc., 1994.
  18. "Recognition of Health Hazards in Industry," Burgess, W. A., John Wiley & Sons, 1981.
  19. PRO-ACT Fact Sheet "Product Substitution," November 1998.

P-D-680: Friend or Foe?
Although once used extensively by maintenance technicians as a general-purpose degreaser and precision-cleaning agent, considerable debate has surfaced in the Department of Defense (DoD) community during the past few years over the continued use of P-D-680. Stricter environmental regulations, higher waste disposal costs, rumors of significant health effects, and the emergence of more "environmentally friendly" cleaning products have all contributed to a general decline in the use of P-D-680 in equipment maintenance and repair. What follows is a brief summary of P-D-680; what it is, what its effects are on human health and the environment, and how it is regulated. Also included is a discussion on a recent investigation by the DoD on P-D-680 uses and potential alternative products.

What is P-D-680?

The name P-D-680 is actually a form of military "slang" and is derived from the Federal Specification designation that governs its procurement. Throughout industry, it is more commonly referred to as stoddard solvent, dry cleaning safety solvent, naphtha safety solvent, or mineral spirits. A clear liquid with a kerosene-like odor, it is mixture of hydrocarbons that is derived through the refinement of crude oil. Because it is a petroleum solvent, P-D-680 is very efficient at dissolving and removing most greases and oils from metal and plastic parts. Federal Specification P-D-680B, "Dry Cleaning and Degreasing Solvent," identifies three general types of the solvent that are classified according to their flash point [in degrees Fahrenheit (oF)]:

  • Type I > 100°F
  • Type II > 140°F
  • Type III > 200°F
In addition to these three general types of P-D-680, there are also Types IA and IIA which are low residue derivations of Types I and II respectively.

What are the potential health impacts of P-D-680?

A number of studies have been performed in an attempt to quantify the health risk(s) associated with exposure to P-D-680. These studies are summarized in the "Toxicological Profile for Stoddard Solvent" published in 1995 by the U.S Department of Health and Human Services' Agency for Toxic Substances and Disease Registry (ATSDR). P-D-680 is considered to be mildly toxic by inhalation which can lead to dizziness, headaches, and/or prolonged reaction times; however this study was performed using an exposure that was significantly higher than the occupational exposures allowed under federal law and Air Force regulations. Other studies indicate that P-D-680 is a mild throat, skin, and eye irritant. According to the profile, P-D-680 has not been classified by any national or international agency as a confirmed or suspected human carcinogen. There is also no evidence that P-D-680 causes birth defects, reproductive effects (infertility), or effects on the immune and lymphatic systems. Finally, regarding the toxicity and carcinogenicity of P-D-680, it is important to note that Federal Specification P-D-680 specifically states that "the solvent shall have no adverse effects on human health when it is used as intended." It also specifically prohibits the inclusion of any chemicals in the solvent, at concentrations of 0.1% or greater, that are listed as carcinogens.

One of the chief complaints from individuals who work with P-D-680 is the odor. At best, defining an odor as either "bad" or "acceptable" is difficult because odor tolerance is highly subjective and can vary greatly from individual to individual. It is important though to distinguish between a "bad" odor and a potentially harmful situation. The maximum safe concentration of P-D-680, established by the American Conference of Government Industrial Hygienists (ACGIH), that workers may be exposed to for eight hours a day, five days a week is 100 parts per million (ppm). The reported odor threshold, or concentration at which most people can begin to smell P-D-680 in the air, is about 0.34 ppm. Therefore, simply smelling P-D-680 does not mean that an individual is being harmed by it. Odors associated with P-D-680 can usually be resolved with proper ventilation and/or by switching to Type IIIA P-D-680 which is specially formulated to be "low odor."

What are the potential environmental impacts of P-D-680?

P-D-680 is a mixture of various hydrocarbon components, making it difficult to accurately predict how it will behave if it is released into the environment. Some portions will volatilize rapidly into the atmosphere, while other portions may be degraded by naturally occurring organisms found in soil and water. The rate of degradation is unknown, however a study on fuel oil #2, which is similar to P-D-680, indicated that 86-90% of the original product will degrade within one year. There is currently no information available on the bioaccumulation potential of P-D-680 in either aquatic or land-based organisms. There is some data suggesting that some of the components of P-D-680 may accumulate in certain animals; however, levels of these components in the animals dissipated quickly after they were removed from exposure to the hydrocarbons.

How is P-D-680 regulated?

From a regulatory standpoint, all cleaning agents, regardless of their original chemical make-up, have the potential to become hazardous wastes when they are disposed of due to contamination from hazardous constituents obtained during the cleaning process. This aside, Type I P-D-680, because of its relatively low flash point, must be disposed of as an ignitable hazardous waste in accordance with Title 40 Code of Federal Regulations (CFR) 261 Subpart C, "Hazardous Waste Characteristics." Conversely, Types II and III, because of their higher flash points, do not meet this threshold for classification as an ignitable hazardous waste. None of the P-D-680 varieties meet the definitions of reactivity, corrosivity, or toxicity contained in Title 40 CFR Subpart C, nor are they listed in Title 40 CFR Subpart D, "Lists of Hazardous Wastes." P-D-680 is not classified as a toxic chemical requiring reporting under Section 313 of the Emergency Planning and Community Right-to-know Act (EPCRA). It is also not classified as an EPCRA extremely hazardous substance (EHS) or a hazardous substance under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

Revisions to Federal Specification P-D-680

In order to eliminate many of the problems associated with the use of P-D-680 Types I and II noted above, a tri-service working group was formed to combine each services' efforts in finding environmentally preferable alternative products. This working group, known as the "Joint Services Working Group on the Minimization of Petroleum Distillate Solvents for Military Applications," conducted user surveys, a market study, laboratory evaluations, and field demonstrations on a number of potential alternative products. As a result of this investigation, the P-D-680 specification is being revised to allow for the qualification of alternative products. One of the most significant revisions is the addition of a new type, Type IV, that includes terpene-hydrocarbon blend products which are equivalent in performance to the existing Type II products. Information on the revision to the P-D-680 specification, as well as the working group's investigation, can be found on the Air Force Corrosion Prevention and Control Office's World Wide Web site at


P-D-680 is a well known and well characterized petroleum-based solvent. It's health and environmental impacts are minor in comparison to most other cleaners in this class, comparable to aqueous-based cleaners in many respects. P-D-680 is not a "universal cleaner" that will solve all your parts washing needs; however, it is also not an "evil solvent" as many have come to believe. The decision to use or not use P-D-680, or any other cleaning agent, should be based on an objective analysis of performance needs, cost, and overall risk.