Aerospace industries have been significantly affected by the enormous growth in environmental and community noise regulations passed primarily in the United States and Europe since the 1970s. Legislation such as the Clean Water Act, the Clean Air Act and the Resource Conservation and Recovery Act in the United States and companion Directives in the European Union have resulted in voluminous local regulations to meet environmental quality objectives. These regulations typically enforce the use of best available technology, whether new materials or processes or end of stack control equipment. Additionally, universal issues such as ozone depletion and global warming are forcing changes to traditional operations by banning chemicals such as chlorofluorocarbons entirely unless exceptional conditions exist.
Early legislation had little impact on aerospace operations until the 1980s. The continued growth of the industry and the concentration of operations around airports and industrialized areas made regulation attractive. The industry underwent a revolution in terms of programmes required to track and manage toxic emissions to the environment with the intent to ensure safety. Wastewater treatment from metal finishing and aircraft maintenance became standard at all large facilities. Hazardous waste segregation, classification, manifesting and, later, treatment prior to disposal were instituted where rudimentary programmes had previously existed. Clean-up programmes at disposal sites became major economic issues for many companies as costs rose to many millions at each site. In the later 1980s and early 1990s, air emissions, which constitute as much as 80% or more of the total emissions from aircraft manufacturing and operation, became the focus of regulation. The International Civil Aviation Organization (ICAO) adopted engine emission standards as early as 1981 (ICAO 1981).
Chemical emissions regulations affect essentially all chemical processing, engine and auxiliary power unit, fuelling and ground service vehicle operations. In Los Angeles, for example, ground-level ozone and carbon monoxide reductions to achieve Clean Air Act standards could require a reduction of 50% of flight operations at Los Angeles International Airport by the year 2005 (Donoghue 1994). Emissions there will be tracked daily to ensure limits on total emissions of volatile organic compounds and carbon monoxide are below the overall total permitted. In Sweden, a tax has been levied on aircraft carbon dioxide emissions due to their global warming potential. Similar regulations in some regions have resulted in a near total elimination of vapour degreasing using chlorinated solvents such as trichloroethane due to the historically high levels of emissions from open-topped degreasers and the ozone depleting potential and toxicity of 1,1,1 trichloroethane.
Perhaps the most broad-based regulation yet imposed is the Aerospace National Emission Standard for Hazardous Air Pollutants (NESHAP) of 1995, promulgated by the United States Environmental Protection Agency under the Clean Air Act Amendments of 1990. This regulation requires all aerospace operations to comply with the average of the best 12% of the current United States control practices to reduce the emission of pollutants from the processes of greatest emissions. The standard requires compliance by September 1998. The processes and materials most affected are manual wipe and flush cleaning, primers and topcoats, paint removal and chemical milling maskants. The regulation allows process change or control and charges local authorities with enforcement of material, equipment, work practice and record-keeping requirements. The significance of these rules is the imposition of the best practices with little regard to cost on every aerospace manufacturer. They force a comprehensive change to low vapour pressure solvent cleaning materials and to coatings low in solvent content, as well as application equipment technology as shown in table 1. Some exceptions were made where product safety or personnel safety (due to fire hazard and so on) would be compromised.
Table 1. Summary of the United States NESHAP in manufacturing and reworking facilities.
|Manual wipe cleaning of aerospace components||
Maximum composite pressure of 45 mmHg at 20 °C or use of specific preferred cleaners
Exemptions for confined spaces, work near energized systems, etc.
Immediate enclosure of wipers to contain further evaporation
|Flush cleaning with VOCs2 or HAPs3 containing materials||Collection and containment of fluids|
|Application of primers and topcoats||Use of high transfer efficiencyequipment4|
|Primer HAP content less water||350 g/l of primer as applied on average5|
|Top coat HAP content water||420 g/l of topcoat as applied on average5|
|Exterior surface paint removal||
Zero HAP chemicals, mechanical blast, high-intensity light6.
Allowance for 6 assembled aircraft to be depainted per site/year with HAP-containing chemicals
|Coatings containing inorganic HAPs||High efficiency control of particulate emissions|
|Chemical milling mask HAP content less water||160 g/l of material as applied or a high-efficiency vapour collection and control system|
|Overspray from coating operations with HAP||Multistage particulate filter|
|Air pollution control equipment||Minimum acceptable efficiencies plus monitoring|
|Spray gun cleaning||No atomization of cleaning solvent, provisions to capture waste|
1 Considerable record keeping, inspection and other requirements apply, not listed here.
2 Volatile organic compounds. These have been shown to be photochemical reactive and precursors to ground-level ozone formation.
3 Hazardous air pollutants. These are 189 compounds listed by the US Environmental Protection Agency as toxic.
4 Listed equipment includes electrostatic or high-volume, low-pressure (HVLP) spray guns.
5 Specialty coatings and other low-emission processes excluded.
6 Touch-up allowed using 26 gallons per aircraft per year of HAP-containing remover (commercial), or 50 gallons per year (military).
Source: US EPA Regulation: 40 CFR Part 63.
Summaries of typical chemical hazards and emission-control practices due to the impact of environmental regulations on manufacturing and maintenance operations in the United States are provided in table 2 and table 3 respectively. European regulations have for the most part not kept pace in the area of toxic air emissions, but have placed greater emphasis on the elimination of toxins, such as cadmium, from the products and the accelerated phase-out of ozone depleter compounds. The Netherlands require operators to justify the use of cadmium as essential for flight safety, for example.
Table 2. Typical chemical hazards of manufacturing processes.
|Common processes||Type of emission||Chemicals or hazards|
|Coatings, including temporary protective coatings, mask and paints||
Overspray of solids and evaporation of solvents
Solid waste, (e.g., wipers)
Volatile organic compouds (VOCs) including methyl ethyl ketone, toluene, xylenes
Ozone-depleting compounds (ODCs) (chlorofluorocarbons, trichloroethane and others)
Organic toxins including tricholorethane, xylene, toluene
Inorganic toxins including cadmium, chromates, lead
VOCs or toxins as above
Evaporation of solvents
Solid waste (wipers)
VOCs, ozone depletersor toxins
VOCs or toxins
Waste solvent (VOCs) and/or contaminated water
Evaporation or entrainment of solvents
Corrosive liquid waste
Dust, heat, light
VOCs such as xylene, toluene, methyl ethyl ketone
Organic toxins (methylene chloride, phenolics)
Heavy metals (chromates)
Caustics and acids including formic acid
Toxic dust (blasting), heat (thermal stripping) and light
Concentrated acid usually chromic, nitric and hydrofluoric
|Plating hard metals||
Heavy metals, acids, complexed cyanides
Heavy metals, acids, complexed cyanides
|Chemical milling||Liquid waste||Caustics and heavy metals, other metals|
Heavy metals, trace amounts of toxic organics
|Alodining (conversion coating)||
Chromates, possibly complexed cyanide
|Corrosion-inhibiting ompounds||Particulates, solid waste||Waxes, heavy metals and toxic organics|
|Composite fabrication||Solid waste||Uncured volatiles|
|Vapour degreasing||Escaped vapour||Tricholorethane, trichoroethylene, perchloroethylene|
|Aqueous degreasing||Liquid waste||VOCs, silicates, trace metals|
|Processes||Air emissions||Water emissions||Land emissions|
|Coating: overspray||Emission control equipment1 for overspray (VOCs and solid particulate)||Onsite pretreatment and monitoring||Treat and landfill3 paint-booth waste. Incinerate flammables and landfill ash. Recycle solvents where possible.|
|Solvent cleaning with VOCs||Emission controls2 and/or material substitution||Onsite pretreatment and monitoring||Incinerate and landfill used wipers|
|Solvent cleaning with ODCs||Substitution due to ban on ODCs production||None||None|
|Solvent cleaning with toxins||Substitution||Onsite pretreatment and monitoring||Treat to reduce toxicity4 and landfill|
|Paint removal||Emission controls or substitution with non-HAP or mechanical methods||Onsite pretreatment and monitoring||Treatment sludge stabilized and landfilled|
|Anodizing aluminium, plating hard metals, chemical milling and immersion conversion coating (Alodine)||Emission control (scrubbers) and/or substitution in some cases||Onsite pretreatment of rinsewaters. Acid and caustic concentrates treated on or off site||Treatment sludge stabilized and landfilled. Other solid waste treated and landfilled|
|Sealing||Usually none required||Usually none required||Incinerate and landfill used wipers|
|Corrosion-inhibiting compounds||Ventilation filtered||Usually none required||Wipers, residual compound and paint-booth filters5 treated and landfilled|
|Vapour degreasing||Chillers to recondense vapours Enclosed systems, or Activated carbon collection||Degreasing solvent separation from wastewater||Toxic degreasing solvent recycled, residual treated and landfilled|
|Aqueous degreasing||Usually none required||Onsite pretreatment and monitoring||Pretreatment sludge managed as hazardous waste|
1 Most aerospace facilities are required to own an industrial wastewater pretreatment facility. Some may have full treatment.
2 Control efficiency usually must be greater than 95% removal/destruction of incoming concentrations. Commonly 98% or greater is achieved by activated carbon or thermal oxidation units.
3 Strict regulations on landfilling specify treatment and landfill construction and monitoring.
4 Toxicity is measured by bioassay and/or leaching tests designed to predict results in solid waste landfills.
5 Usually filtered paint booths. Work done out of sequence or touch up, etc. is usually exempt due to practical considerations.
Noise regulations have followed a similar course. The United States Federal Aviation Administration and the International Civil Aviation Organization have set aggressive targets for the improvement of jet engine noise reduction (e.g., the United States Airport Noise and Capacity Act of 1990). Airlines are faced with the option of replacing older aircraft such as the Boeing 727 or McDonnell Douglas DC-9 (Stage 2 aircraft as defined by the ICAO) with new generation airplanes, re-engining or retrofitting these aircraft with “hush” kits. Elimination of noisy Stage 2 aircraft is mandated by 31 December 1999 in the United States, when Stage 3 rules take effect.
Another hazard posed by aerospace operation is the threat of falling debris. Items such as waste, aircraft parts and satellites descend with varying degrees of frequency. The most common in terms of frequency is the so-called blue ice which results when leaking toilet system drains allow waste to freeze outside the aircraft and then separate and fall. Aviation authorities are considering rules to require additional inspection and correction of leaking drains. Other hazards such as satellite debris may occasionally be hazardous (e.g., radioactive instruments or power sources), but present extremely low risk to the public.
Most companies have formed organizations to address emission reduction. Goals for environmental performance are established and policies are in place. Management of the permits, safe material handling and transportation, disposal and treatment require engineers, technicians and administrators.
Environmental engineers, chemical engineers and others are employed as researchers and administrators. In addition, programmes exist to help remove the source of chemical and noise emissions within the design or the process.