Chemical cleaning can sometimes be substituted for solvent cleaning to reduce the amount of toxic or hazardous chemicals used during the cleaning operation. Aqueous chemical cleaning is an example of an effective method of parts washing. Aqueous cleaners are generally environmentally friendly because the constituents are typically less toxic than solvents and do not contain ozone depleting substances (ODS). Chemical cleaning is useful in a broad spectrum of cleaning applications. It can be more efficient than other methods of washing if the cleaning chemical used, the residue/dirt being removed, and the substrate materials are strategically matched.

Solvent cleaning can be distinguished from chemical cleaning by reaction to the target residue. During solvent cleaning, a specific solvent is used to dissolve the residue in or on the object to be cleaned, whereas a chemical cleaner acts by initiating a chemical reaction to remove the residue from the object. Chemical cleaners include products such as bleach, which is an oxidizer. Other frequently used chemical cleaners are acids and bases. Acids are typically used to remove mineral deposits or scale from surfaces, while bases or alkaline solutions react with most carbonaceous residues; for example, oil and grease buildup. The acidity (or alkalinity) of the solutions will be depleted by the chemical action, and any excess solution can be easily neutralized.

In general, aqueous chemical cleaners work best at elevated temperatures. Typical temperature ranges are 140°F to 190°F. It is estimated that for every 20-degree difference in temperature, cleaning efficiency either increases or decreases by 50%. The temperature range used in a typical aqueous cleaning process will depend on a number of factors, all of which affect one another.

In aqueous precision cleaning operations, high quality water for cleaner make-up and rinsewaters is necessary. High quality water is classified as "pure" water, which means that the natural minerals and dissolved salts found in water supplies must be removed. The importance of high quality water is often overlooked in chemical cleaning operations. If rinsewater is contaminated with impurities, varying all the other parameters of the process will not compensate or improve the end result of the cleaning process.

Chemical cleaning may allow a facility to use less toxic materials to get the same results as cleaning with a solvent. It is possible that a decrease in chemical cleaning solvents on site will sufficiently reduce the amount stored on site to achieve a level below any of the reporting thresholds of SARA Title III for solvents (40 CFR 355, 370, and 372; and EO 12856). In addition, the use of less toxic chemicals may decrease the need for a facility to obtain an air permit (40 CFR 70 and 71) and enable them to meet NESHAPs requirements for halogenated solvent cleaning under 40 CFR 63.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

Material compatibility issues depend on the material to be cleaned. For example, highly alkaline (caustic) chemicals with a pH above 12 can etch aluminum, while acidic substances can cause hydrogen embrittlement in some steels. In addition, certain steels are prone to flash rusting so certain preventative measures must be taken. Be sure to check with the appropriate authorities prior to using a new cleaning technique.

Mild acids and bases can cause irritation to the skin and mucous membranes. The effects vary by chemical. Proper personal protective equipment should always be used.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any of these technologies.

• Replaces hazardous solvents with biodegradable detergents
• Spent water or detergent solutions may be discharged into the local sewer system if they meets the discharge regulations
• Reduces exposure to carcinogenic and neurotoxic chemicals
• Superior ability for removing particles
• Neutralizes the static charge of the item
• Generally, reduced disposal expenses. However, at Naval Air Station North Island, aqueous parts water costs were not proven to be lower than solvent costs.
• Meets state and local air regulations regarding ozone depleting substances (ODSs)
• If properly engineered, reduces cleaning times

• Spent water or detergent waste water or sludge may require pretreatment (where pretreatment is allowed)
• Increases water consumption
• May require rinsing, drying and oven stations
• Typically occupies more floor space
• Some of the solvents (e.g., P-D-680 Type II) can be recycled
• The chemicals used may be more dangerous to human life or the object being cleaned than the alternative solvent

The costs incurred will vary depending upon the material being cleaned, the volume of cleaning required, and the contaminant(s) being removed. According to the Naval Air Station North Island, economic data is specific to each application, and comparisons between other systems would not be applicable.

The principle costs that need to be considered are:

• capital expenses based on required or anticipated cleaning volume
• floor space considerations for the system being evaluated.
• a comparison of disposal/recycling costs for the solvent versus equivalent costs for the chemical chosen to replace the solvent
• any additional personal protective equipment (PPE) which might be necessary
• any special handling or storage considerations for the solvent or chemical in question

Approval is controlled locally and should be implemented only after engineering approval has been granted. Major claimant approval is not required.