Base Maintenance Operations and Hazards
Maintenance hangars are very large structures capable of accommodating numerous aircraft. The largest hangars can simultaneously accommodate several wide-body aircraft, such as the Boeing 747. Separate work areas, or bays, are assigned to each aircraft undergoing maintenance. Specialized shops for the repair and refitting of components are associated with the hangars. Shop areas typically include sheet metal, interiors, hydraulics, plastics, wheels and brakes, electrical and avionics and emergency equipment. Separate welding areas, paint shops and non-destructive testing areas may be established. Parts-cleaning operations are likely to be found throughout the facility.
Paint hangars with high ventilation rates for workplace air contaminant controls and environmental pollution protection should be available if painting or paint stripping is to be performed. Paint strippers often contain methylene chloride and corrosives, including hydrofluoric acid. Aircraft primers typically contain a chromate component for corrosion protection. Top coats may be epoxy or polyurethane based. Toluene diisocyanate (TDI) is now seldom used in these paints, having been replaced with higher molecular weight isocyanates such as 4,4-diphenylmethane diisocyanate (MDI) or by prepolymers. These still present a risk of asthma if inhaled.
Engine maintenance may be performed within the maintenance base, at a specialized engine overhaul facility or by a sub-contractor. Engine overhaul requires the use of metalworking techniques including grinding, blasting, chemical cleaning, plating and plasma spray. Silica has in most cases been replaced with less hazardous materials in parts cleaners, but the base materials or coatings may create toxic dusts when blasted or ground. Numerous materials of worker health and environmental concern are used in metal cleaning and plating. These include corrosives, organic solvents and heavy metals. Cyanide is generally of the greatest immediate concern, requiring special emphasis in emergency preparedness planning. Plasma spray operations also merit particular attention. Finely divided metals are fed into a plasma stream generated using high-voltage electrical sources and plated onto parts with the concomitant generation of very high noise levels and light energies. Physical hazards include work at height, lifting and work in uncomfortable positions. Precautions include local exhaust ventilation, PPE, fall protection, training in proper lifting and use of mechanized lifting equipment when possible and ergonomic redesign. For example, repetitive motions involved in tasks such as wire tying may be reduced by use of specialized tools.
Aviation gasoline, used in some propeller-driven aircraft, is highly flammable. Military aircraft engines, including those on transport aircraft, may use less noise abatement than those on commercial aircraft and may be augmented by afterburners. Aboard aircraft carriers the many hazards are significantly increased. Engine noise is augmented by steam catapults and afterburners, flight deck space is extremely limited, and the deck itself is in motion. Because of combat demands, asbestos insulation is present in some cockpits and around hot areas.
The need for lowered radar visibility (stealth) has resulted in the increased use of composite materials on fuselage, wings and flight control structures. These areas may be damaged in combat or from exposure to extremes of climate, requiring extensive repair. Repairs performed under field conditions may result in heavy exposures to resins and composite dusts. Beryllium is also common in military applications. Hydrazide may be present as part of auxiliary-power units, and anti-tank armament may include radioactive depleted uranium rounds. Precautions include appropriate PPE, including respiratory protection. Where possible, portable exhaust systems should be used.
Maintenance work on agricultural aircraft (crop dusters) may result in exposures to pesticides either as a single product or, more likely, as a mixture of products contaminating a single or multiple aircraft. Degradation products of some pesticides are more hazardous than the parent product. Dermal routes of exposure may be significant and may be enhanced by perspiration. Agricultural aircraft and external parts should be thoroughly cleaned before repair, and/or PPE, including skin and respiratory protection, should be used.